diff --git a/api.go b/api.go
index d9f3876d..3c773daf 100644
--- a/api.go
+++ b/api.go
@@ -8,6 +8,7 @@ import (
 
 	"github.com/gagliardetto/solana-go"
 	"github.com/rpcpool/yellowstone-faithful/compactindexsized"
+	"github.com/rpcpool/yellowstone-faithful/slottools"
 	"github.com/valyala/fasthttp"
 )
 
@@ -35,7 +36,7 @@ func (multi *MultiEpoch) apiHandler(reqCtx *fasthttp.RequestCtx) {
 			return
 		}
 		// find the epoch that contains the requested slot
-		epochNumber := CalcEpochForSlot(slot)
+		epochNumber := slottools.CalcEpochForSlot(slot)
 		epochHandler, err := multi.GetEpoch(epochNumber)
 		if err != nil {
 			reqCtx.SetStatusCode(fasthttp.StatusNotFound) // TODO: this means epoch is not available, and probably should be another dedicated status code
diff --git a/blocktimeindex/error.go b/blocktimeindex/error.go
new file mode 100644
index 00000000..b8873484
--- /dev/null
+++ b/blocktimeindex/error.go
@@ -0,0 +1,26 @@
+package blocktimeindex
+
+import "fmt"
+
+var _ error = &ErrSlotOutOfRange{}
+
+type ErrSlotOutOfRange struct {
+	start, end uint64
+	slot       uint64
+}
+
+func NewErrSlotOutOfRange(start, end, slot uint64) error {
+	return &ErrSlotOutOfRange{start: start, end: end, slot: slot}
+}
+
+func (e *ErrSlotOutOfRange) Error() string {
+	if e == nil {
+		return "nil"
+	}
+	return fmt.Sprintf("slot %d is out of range [%d, %d]", e.slot, e.start, e.end)
+}
+
+func (e *ErrSlotOutOfRange) Is(target error) bool {
+	_, ok := target.(*ErrSlotOutOfRange)
+	return ok
+}
diff --git a/blocktimeindex/writer.go b/blocktimeindex/writer.go
new file mode 100644
index 00000000..df0fe821
--- /dev/null
+++ b/blocktimeindex/writer.go
@@ -0,0 +1,259 @@
+package blocktimeindex
+
+import (
+	"bytes"
+	"encoding/binary"
+	"fmt"
+	"io"
+	"math"
+	"os"
+
+	"github.com/ipfs/go-cid"
+	"github.com/rpcpool/yellowstone-faithful/indexes"
+	"github.com/rpcpool/yellowstone-faithful/slottools"
+)
+
+// Using an int32 for blocktime is enough seconds until the year 2106.
+
+var magic = []byte("blocktimeindex")
+
+type Index struct {
+	start    uint64
+	end      uint64
+	epoch    uint64
+	capacity uint64
+	values   []int64
+}
+
+func NewIndexer(start, end, capacity uint64) *Index {
+	epoch := slottools.EpochForSlot(start)
+	if epoch != slottools.EpochForSlot(end) {
+		panic(fmt.Sprintf("start and end slots must be in the same epoch: %d != %d", epoch, slottools.EpochForSlot(end)))
+	}
+	return &Index{
+		start:    start,
+		end:      end,
+		epoch:    epoch,
+		capacity: capacity,
+		values:   make([]int64, capacity),
+	}
+}
+
+const DefaultCapacityForEpoch = 432_000
+
+// NewForEpoch creates a new Index for the given epoch.
+func NewForEpoch(epoch uint64) *Index {
+	start, end := slottools.CalcEpochLimits(epoch)
+	return NewIndexer(start, end, DefaultCapacityForEpoch)
+}
+
+// Set sets the blocktime for the given slot.
+func (i *Index) Set(slot uint64, time int64) error {
+	if slot < i.start || slot > i.end {
+		return NewErrSlotOutOfRange(i.start, i.end, slot)
+	}
+	i.values[slot-i.start] = time
+	return nil
+}
+
+// Get gets the blocktime for the given slot.
+func (i *Index) Get(slot uint64) (int64, error) {
+	if slot < i.start || slot > i.end {
+		return 0, NewErrSlotOutOfRange(i.start, i.end, slot)
+	}
+	return i.values[slot-i.start], nil
+}
+
+func (i *Index) marshalBinary() ([]byte, error) {
+	writer := bytes.NewBuffer(nil)
+	writer.Grow(DefaultIndexByteSize)
+	_, err := writer.Write(magic)
+	if err != nil {
+		return nil, fmt.Errorf("failed to write magic: %w", err)
+	}
+	_, err = writer.Write(slottools.Uint64ToLEBytes(i.start))
+	if err != nil {
+		return nil, fmt.Errorf("failed to write start: %w", err)
+	}
+	_, err = writer.Write(slottools.Uint64ToLEBytes(i.end))
+	if err != nil {
+		return nil, fmt.Errorf("failed to write end: %w", err)
+	}
+	_, err = writer.Write(slottools.Uint64ToLEBytes(i.epoch))
+	if err != nil {
+		return nil, fmt.Errorf("failed to write epoch: %w", err)
+	}
+	_, err = writer.Write(slottools.Uint64ToLEBytes(i.capacity))
+	if err != nil {
+		return nil, fmt.Errorf("failed to write capacity: %w", err)
+	}
+	for _, t := range i.values {
+		b, err := blocktimeToBytes(int64(t))
+		if err != nil {
+			return nil, fmt.Errorf("failed to convert time to bytes: %w", err)
+		}
+		_, err = writer.Write(b)
+		if err != nil {
+			return nil, fmt.Errorf("failed to write time: %w", err)
+		}
+	}
+	return writer.Bytes(), nil
+}
+
+func (i *Index) MarshalBinary() ([]byte, error) {
+	return i.marshalBinary()
+}
+
+var _ io.WriterTo = (*Index)(nil)
+
+// WriteTo implements io.WriterTo.
+func (i *Index) WriteTo(wr io.Writer) (int64, error) {
+	data, err := i.marshalBinary()
+	if err != nil {
+		return 0, err
+	}
+	n, err := wr.Write(data)
+	return int64(n), err
+}
+
+func blocktimeToBytes(blocktime int64) ([]byte, error) {
+	if blocktime < 0 {
+		return nil, fmt.Errorf("blocktime must be non-negative")
+	}
+	if blocktime > math.MaxUint32 {
+		return nil, fmt.Errorf("blocktime must fit in 32 bits")
+	}
+	// treat as uint32
+	buf := make([]byte, 4)
+	binary.LittleEndian.PutUint32(buf, uint32(blocktime))
+	return buf, nil
+}
+
+func (i *Index) unmarshalBinary(data []byte) error {
+	reader := bytes.NewReader(data)
+	magicBuf := make([]byte, len(magic))
+	_, err := reader.Read(magicBuf)
+	if err != nil {
+		return fmt.Errorf("failed to read magic: %w", err)
+	}
+	if !bytes.Equal(magicBuf, magic) {
+		return fmt.Errorf("invalid magic: %s", magicBuf)
+	}
+
+	startBuf := make([]byte, 8)
+	_, err = reader.Read(startBuf)
+	if err != nil {
+		return fmt.Errorf("failed to read start: %w", err)
+	}
+	i.start = slottools.Uint64FromLEBytes(startBuf)
+
+	endBuf := make([]byte, 8)
+	_, err = reader.Read(endBuf)
+	if err != nil {
+		return fmt.Errorf("failed to read end: %w", err)
+	}
+	i.end = slottools.Uint64FromLEBytes(endBuf)
+
+	epochBuf := make([]byte, 8)
+	_, err = reader.Read(epochBuf)
+	if err != nil {
+		return fmt.Errorf("failed to read epoch: %w", err)
+	}
+	i.epoch = slottools.Uint64FromLEBytes(epochBuf)
+	{
+		// check that start and end are in the same epoch
+		startEpoch := slottools.EpochForSlot(i.start)
+		endEpoch := slottools.EpochForSlot(i.end)
+		if startEpoch != endEpoch {
+			return fmt.Errorf("start and end slots must be in the same epoch: %d != %d", startEpoch, endEpoch)
+		}
+		if startEpoch != i.epoch {
+			return fmt.Errorf("epoch mismatch: start=%d, end=%d, epoch=%d", startEpoch, endEpoch, i.epoch)
+		}
+	}
+
+	capacityBuf := make([]byte, 8)
+	_, err = reader.Read(capacityBuf)
+	if err != nil {
+		return fmt.Errorf("failed to read capacity: %w", err)
+	}
+	i.capacity = slottools.Uint64FromLEBytes(capacityBuf)
+
+	i.values = make([]int64, i.capacity)
+	for j := uint64(0); j < i.capacity; j++ {
+		timeBuf := make([]byte, 4)
+		_, err = reader.Read(timeBuf)
+		if err != nil {
+			return fmt.Errorf("failed to read time: %w", err)
+		}
+		i.values[j] = int64(binary.LittleEndian.Uint32(timeBuf))
+	}
+	return nil
+}
+
+func (i *Index) UnmarshalBinary(data []byte) error {
+	return i.unmarshalBinary(data)
+}
+
+func (i *Index) FromBytes(data []byte) error {
+	return i.unmarshalBinary(data)
+}
+
+func (i *Index) FromReader(r io.Reader) error {
+	data, err := io.ReadAll(r)
+	if err != nil {
+		return fmt.Errorf("failed to read data: %w", err)
+	}
+	return i.FromBytes(data)
+}
+
+func (i *Index) FromFile(file string) error {
+	buf, err := os.ReadFile(file)
+	if err != nil {
+		return fmt.Errorf("failed to read file: %w", err)
+	}
+	return i.FromBytes(buf)
+}
+
+func FromFile(file string) (*Index, error) {
+	i := &Index{}
+	err := i.FromFile(file)
+	if err != nil {
+		return nil, err
+	}
+	return i, nil
+}
+
+func FromBytes(data []byte) (*Index, error) {
+	i := &Index{}
+	err := i.FromBytes(data)
+	if err != nil {
+		return nil, err
+	}
+	return i, nil
+}
+
+func FromReader(r io.Reader) (*Index, error) {
+	i := &Index{}
+	err := i.FromReader(r)
+	if err != nil {
+		return nil, err
+	}
+	return i, nil
+}
+
+func FormatFilename(epoch uint64, rootCid cid.Cid, network indexes.Network) string {
+	return fmt.Sprintf(
+		"epoch-%d-%s-%s-%s",
+		epoch,
+		rootCid.String(),
+		network,
+		"slot-to-blocktime.index",
+	)
+}
+
+var DefaultIndexByteSize = len(magic) + 8 + 8 + 8 + 8 + (432000 * 4)
+
+func (i *Index) Epoch() uint64 {
+	return i.epoch
+}
diff --git a/blocktimeindex/writer_test.go b/blocktimeindex/writer_test.go
new file mode 100644
index 00000000..32ac18a9
--- /dev/null
+++ b/blocktimeindex/writer_test.go
@@ -0,0 +1,121 @@
+package blocktimeindex
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestWriter(t *testing.T) {
+	{
+		epoch := uint64(0)
+		w := NewForEpoch(epoch)
+		if w.start != 0 {
+			t.Errorf("expected 0, got %v", w.start)
+		}
+		if w.end != 431999 {
+			t.Errorf("expected 431999, got %v", w.end)
+		}
+		if w.epoch != 0 {
+			t.Errorf("expected 0, got %v", w.epoch)
+		}
+		if w.capacity != 432000 {
+			t.Errorf("expected 432000, got %v", w.capacity)
+		}
+		if len(w.values) != 432000 {
+			t.Errorf("expected 432000, got %v", len(w.values))
+		}
+		err := w.Set(0, 1)
+		if err != nil {
+			t.Errorf("expected no error, got %v", err)
+		}
+		if got, err := w.Get(0); got != 1 || err != nil {
+			t.Errorf("expected 1, got %v, %v", got, err)
+		}
+		err = w.Set(431999, 1)
+		if err != nil {
+			t.Errorf("expected no error, got %v", err)
+		}
+		if got, err := w.Get(431999); got != 1 || err != nil {
+			t.Errorf("expected 1, got %v, %v", got, err)
+		}
+		err = w.Set(432000, 1)
+		if !errors.Is(err, &ErrSlotOutOfRange{}) {
+			t.Errorf("expected ErrSlotOutOfRange, got %v", err)
+		}
+		// expect error when getting out of range slot
+		if _, err := w.Get(432000); !errors.Is(err, &ErrSlotOutOfRange{}) {
+			t.Errorf("expected ErrSlotOutOfRange, got %v", err)
+		}
+	}
+	{
+		epoch := uint64(1)
+		w := NewForEpoch(epoch)
+		if w.start != 432000 {
+			t.Errorf("expected 432000, got %v", w.start)
+		}
+		if w.end != 863999 {
+			t.Errorf("expected 863999, got %v", w.end)
+		}
+		if w.epoch != 1 {
+			t.Errorf("expected 1, got %v", w.epoch)
+		}
+		if w.capacity != 432000 {
+			t.Errorf("expected 432000, got %v", w.capacity)
+		}
+		if len(w.values) != 432000 {
+			t.Errorf("expected 432000, got %v", len(w.values))
+		}
+		if len(w.values) != 432000 {
+			t.Errorf("expected 432000, got %v", len(w.values))
+		}
+		err := w.Set(432000, 123)
+		if err != nil {
+			t.Errorf("expected no error, got %v", err)
+		}
+		if got, err := w.Get(432000); got != 123 || err != nil {
+			t.Errorf("expected 1, got %v, %v", got, err)
+		}
+		err = w.Set(863999, 1)
+		if err != nil {
+			t.Errorf("expected no error, got %v", err)
+		}
+		if got, err := w.Get(863999); got != 1 || err != nil {
+			t.Errorf("expected 1, got %v, %v", got, err)
+		}
+		err = w.Set(864000, 1)
+		if !errors.Is(err, &ErrSlotOutOfRange{}) {
+			t.Errorf("expected ErrSlotOutOfRange, got %v", err)
+		}
+		// expect error when getting out of range slot
+		if _, err := w.Get(864000); !errors.Is(err, &ErrSlotOutOfRange{}) {
+			t.Errorf("expected ErrSlotOutOfRange, got %v", err)
+		}
+		{
+			// test writing
+			buf, err := w.MarshalBinary()
+			if err != nil {
+				t.Errorf("expected no error, got %v", err)
+			}
+			// the expected length is:
+			// - len(magic) + len(start) + len(end) + len(capacity) + len(epoch) + (len(values) * 4)
+			expectedLen := DefaultIndexByteSize
+			if len(buf) != expectedLen {
+				t.Errorf("expected %v, got %v", expectedLen, len(buf))
+			}
+			{
+				// test reading
+				got, err := FromBytes(buf)
+				if err != nil {
+					t.Errorf("expected no error, got %v", err)
+				}
+				assert.Equal(t, w.start, got.start)
+				assert.Equal(t, w.end, got.end)
+				assert.Equal(t, w.epoch, got.epoch)
+				assert.Equal(t, w.capacity, got.capacity)
+				assert.Equal(t, w.values, got.values)
+			}
+		}
+	}
+}
diff --git a/cmd-find-missing-tx-meta.go b/cmd-find-missing-tx-meta.go
index bea7704f..21900625 100644
--- a/cmd-find-missing-tx-meta.go
+++ b/cmd-find-missing-tx-meta.go
@@ -16,6 +16,7 @@ import (
 	"github.com/rpcpool/yellowstone-faithful/carreader"
 	"github.com/rpcpool/yellowstone-faithful/ipld/ipldbindcode"
 	"github.com/rpcpool/yellowstone-faithful/iplddecoders"
+	"github.com/rpcpool/yellowstone-faithful/slottools"
 	"github.com/rpcpool/yellowstone-faithful/tooling"
 	"github.com/urfave/cli/v2"
 	"k8s.io/klog/v2"
@@ -188,8 +189,8 @@ func newCmd_find_missing_tx_metadata() *cli.Command {
 						slot := uint64(block.Slot)
 						firstSlot = &slot
 						// determine epoch:
-						epoch := CalcEpochForSlot(slot)
-						epochStart, epochEnd = CalcEpochLimits(epoch)
+						epoch := slottools.CalcEpochForSlot(slot)
+						epochStart, epochEnd = slottools.CalcEpochLimits(epoch)
 					}
 					if tookToDo1kSlots > 0 {
 						remainingSlots := epochEnd - uint64(block.Slot)
diff --git a/cmd-x-index-all.go b/cmd-x-index-all.go
index b4b15eac..7e33d35b 100644
--- a/cmd-x-index-all.go
+++ b/cmd-x-index-all.go
@@ -9,10 +9,12 @@ import (
 	"math/rand"
 	"os"
 	"path/filepath"
+	"sort"
 	"time"
 
 	"github.com/dustin/go-humanize"
 	"github.com/ipfs/go-cid"
+	"github.com/rpcpool/yellowstone-faithful/blocktimeindex"
 	"github.com/rpcpool/yellowstone-faithful/bucketteer"
 	"github.com/rpcpool/yellowstone-faithful/carreader"
 	"github.com/rpcpool/yellowstone-faithful/indexes"
@@ -166,6 +168,10 @@ func createAllIndexes(
 	for kind := range numItems {
 		kinds = append(kinds, kind)
 	}
+	// sort from byte value:
+	sort.Slice(kinds, func(i, j int) bool {
+		return kinds[i] < kinds[j]
+	})
 	for _, kind := range kinds {
 		klog.Infof("  %s: %s items", iplddecoders.Kind(kind), humanize.Comma(int64(numItems[kind])))
 		numTotalItems += numItems[kind]
@@ -220,6 +226,8 @@ func createAllIndexes(
 	}
 	defer sig_exists.Close()
 
+	slot_to_blocktime := blocktimeindex.NewForEpoch(epoch)
+
 	totalOffset := uint64(0)
 	{
 		if size, err := rd.HeaderSize(); err != nil {
@@ -266,6 +274,11 @@ func createAllIndexes(
 				if err != nil {
 					return nil, 0, fmt.Errorf("failed to index slot to cid: %w", err)
 				}
+
+				err = slot_to_blocktime.Set(uint64(block.Slot), int64(block.Meta.Blocktime))
+				if err != nil {
+					return nil, 0, fmt.Errorf("failed to index slot to blocktime: %w", err)
+				}
 				numIndexedBlocks++
 			}
 		case iplddecoders.KindTransaction:
@@ -391,6 +404,24 @@ func createAllIndexes(
 			return nil
 		})
 
+		wg.Go(func() error {
+			klog.Infof("Sealing slot_to_blocktime index...")
+
+			path := filepath.Join(indexDir, blocktimeindex.FormatFilename(epoch, rootCID, network))
+			file, err := os.Create(path)
+			if err != nil {
+				return fmt.Errorf("failed to create slot_to_blocktime index file: %w", err)
+			}
+			defer file.Close()
+
+			if _, err := slot_to_blocktime.WriteTo(file); err != nil {
+				return fmt.Errorf("failed to write slot_to_blocktime index: %w", err)
+			}
+			paths.SlotToBlocktime = path
+			klog.Infof("Successfully sealed slot_to_blocktime index: %s", paths.SlotToBlocktime)
+			return nil
+		})
+
 		if err := wg.Wait(); err != nil {
 			return nil, 0, err
 		}
@@ -412,6 +443,7 @@ type IndexPaths struct {
 	SlotToCid          string
 	SignatureToCid     string
 	SignatureExists    string
+	SlotToBlocktime    string
 }
 
 // IndexPaths.String
@@ -429,6 +461,9 @@ func (p *IndexPaths) String() string {
 	builder.WriteString("  sig_exists:\n    uri: ")
 	builder.WriteString(quoteSingle(p.SignatureExists))
 	builder.WriteString("\n")
+	builder.WriteString("  slot_to_blocktime:\n    uri: ")
+	builder.WriteString(quoteSingle(p.SlotToBlocktime))
+	builder.WriteString("\n")
 	return builder.String()
 }
 
diff --git a/cmd-x-index-gsfa.go b/cmd-x-index-gsfa.go
index 65db5400..edc1697c 100644
--- a/cmd-x-index-gsfa.go
+++ b/cmd-x-index-gsfa.go
@@ -20,6 +20,7 @@ import (
 	"github.com/rpcpool/yellowstone-faithful/indexmeta"
 	"github.com/rpcpool/yellowstone-faithful/ipld/ipldbindcode"
 	"github.com/rpcpool/yellowstone-faithful/iplddecoders"
+	"github.com/rpcpool/yellowstone-faithful/slottools"
 	"github.com/urfave/cli/v2"
 	"k8s.io/klog/v2"
 )
@@ -167,7 +168,7 @@ func newCmd_Index_gsfa() *cli.Command {
 			verifyHash := c.Bool("verify-hash")
 			ipldbindcode.DisableHashVerification = !verifyHash
 
-			epochStart, epochEnd := CalcEpochLimits(epoch)
+			epochStart, epochEnd := slottools.CalcEpochLimits(epoch)
 
 			numSlots := uint64(0)
 			numMaxObjects := uint64(0)
@@ -233,7 +234,6 @@ func newCmd_Index_gsfa() *cli.Command {
 							txWithInfo.Offset,
 							txWithInfo.Length,
 							txWithInfo.Slot,
-							txWithInfo.Blocktime,
 							accountKeys,
 						)
 						if err != nil {
diff --git a/cmd-x-index-slot2blocktime.go b/cmd-x-index-slot2blocktime.go
new file mode 100644
index 00000000..ca6371de
--- /dev/null
+++ b/cmd-x-index-slot2blocktime.go
@@ -0,0 +1,163 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"path/filepath"
+	"time"
+
+	"github.com/ipfs/go-cid"
+	carv2 "github.com/ipld/go-car/v2"
+	"github.com/rpcpool/yellowstone-faithful/blocktimeindex"
+	"github.com/rpcpool/yellowstone-faithful/indexes"
+	"github.com/rpcpool/yellowstone-faithful/ipld/ipldbindcode"
+	"github.com/urfave/cli/v2"
+	"k8s.io/klog/v2"
+)
+
+func newCmd_Index_slot2blocktime() *cli.Command {
+	var epoch uint64
+	var network indexes.Network
+	return &cli.Command{
+		Name:        "slot-to-blocktime",
+		Description: "Given a CAR file containing a Solana epoch, create an index of the file that maps slots to blocktimes.",
+		ArgsUsage:   "<car-path> <index-dir>",
+		Before: func(c *cli.Context) error {
+			if network == "" {
+				network = indexes.NetworkMainnet
+			}
+			return nil
+		},
+		Flags: []cli.Flag{
+			&cli.Uint64Flag{
+				Name:        "epoch",
+				Usage:       "the epoch of the CAR file",
+				Destination: &epoch,
+				Required:    true,
+			},
+			&cli.StringFlag{
+				Name:  "network",
+				Usage: "the cluster of the epoch; one of: mainnet, testnet, devnet",
+				Action: func(c *cli.Context, s string) error {
+					network = indexes.Network(s)
+					if !indexes.IsValidNetwork(network) {
+						return fmt.Errorf("invalid network: %q", network)
+					}
+					return nil
+				},
+			},
+		},
+		Subcommands: []*cli.Command{},
+		Action: func(c *cli.Context) error {
+			carPath := c.Args().Get(0)
+			indexDir := c.Args().Get(1)
+
+			{
+				startedAt := time.Now()
+				defer func() {
+					klog.Infof("Finished in %s", time.Since(startedAt))
+				}()
+				klog.Infof("Creating slot-to-blocktime index for %s", carPath)
+				indexFilepath, err := CreateIndex_slot2blocktime(
+					context.TODO(),
+					epoch,
+					network,
+					carPath,
+					indexDir,
+				)
+				if err != nil {
+					panic(err)
+				}
+				klog.Info("slot-to-blocktime index created at", indexFilepath)
+			}
+			return nil
+		},
+	}
+}
+
+// CreateIndex_slot2blocktime creates an index file that maps slot numbers to blocktimes.
+func CreateIndex_slot2blocktime(
+	ctx context.Context,
+	epoch uint64,
+	network indexes.Network,
+	carPath string,
+	indexDir string,
+) (string, error) {
+	// Check if the CAR file exists:
+	exists, err := fileExists(carPath)
+	if err != nil {
+		return "", fmt.Errorf("failed to check if CAR file exists: %w", err)
+	}
+	if !exists {
+		return "", fmt.Errorf("CAR file %q does not exist", carPath)
+	}
+
+	cr, err := carv2.OpenReader(carPath)
+	if err != nil {
+		return "", fmt.Errorf("failed to open CAR file: %w", err)
+	}
+
+	// check it has 1 root
+	roots, err := cr.Roots()
+	if err != nil {
+		return "", fmt.Errorf("failed to get roots: %w", err)
+	}
+	// There should be only one root CID in the CAR file.
+	if len(roots) != 1 {
+		return "", fmt.Errorf("CAR file has %d roots, expected 1", len(roots))
+	}
+	rootCid := roots[0]
+
+	slot_to_blocktime := blocktimeindex.NewForEpoch(epoch)
+
+	numBlocksIndexed := uint64(0)
+	klog.Infof("Indexing...")
+
+	dr, err := cr.DataReader()
+	if err != nil {
+		return "", fmt.Errorf("failed to get data reader: %w", err)
+	}
+
+	// Iterate over all blocks in the CAR file and put them into the index,
+	// using the slot number as the key and the blocktime as the value.
+	err = FindBlocks(
+		ctx,
+		dr,
+		func(c cid.Cid, block *ipldbindcode.Block) error {
+			slotNum := uint64(block.Slot)
+
+			err = slot_to_blocktime.Set(slotNum, int64(block.Meta.Blocktime))
+			if err != nil {
+				return fmt.Errorf("failed to put cid to offset: %w", err)
+			}
+
+			numBlocksIndexed++
+			if numBlocksIndexed%1_000 == 0 {
+				printToStderr(".")
+			}
+			return nil
+		})
+	if err != nil {
+		return "", fmt.Errorf("failed to index; error while iterating over blocks: %w", err)
+	}
+
+	// Use the car file name and root CID to name the index file:
+
+	klog.Infof("Sealing index...")
+
+	indexFilePath := filepath.Join(indexDir, blocktimeindex.FormatFilename(epoch, rootCid, network))
+
+	file, err := os.Create(indexFilePath)
+	if err != nil {
+		return "", fmt.Errorf("failed to create slot_to_blocktime index file: %w", err)
+	}
+	defer file.Close()
+
+	if _, err := slot_to_blocktime.WriteTo(file); err != nil {
+		return "", fmt.Errorf("failed to write slot_to_blocktime index: %w", err)
+	}
+	klog.Infof("Successfully sealed slot_to_blocktime index")
+	klog.Infof("Index created at %s; %d items indexed", indexFilePath, numBlocksIndexed)
+	return indexFilePath, nil
+}
diff --git a/cmd-x-index.go b/cmd-x-index.go
index 58e58fc1..e51b8bdf 100644
--- a/cmd-x-index.go
+++ b/cmd-x-index.go
@@ -20,6 +20,7 @@ func newCmd_Index() *cli.Command {
 			newCmd_Index_all(), // NOTE: not actually all.
 			newCmd_Index_gsfa(),
 			newCmd_Index_sigExists(),
+			newCmd_Index_slot2blocktime(),
 		},
 	}
 }
diff --git a/config.go b/config.go
index 154b3d98..801014e1 100644
--- a/config.go
+++ b/config.go
@@ -148,6 +148,9 @@ type Config struct {
 		SigExists struct {
 			URI URI `json:"uri" yaml:"uri"`
 		} `json:"sig_exists" yaml:"sig_exists"`
+		SlotToBlocktime struct {
+			URI URI `json:"uri" yaml:"uri"`
+		} `json:"slot_to_blocktime" yaml:"slot_to_blocktime"`
 	} `json:"indexes" yaml:"indexes"`
 	Genesis struct {
 		URI URI `json:"uri" yaml:"uri"`
@@ -365,6 +368,14 @@ func (c *Config) Validate() error {
 				return err
 			}
 		}
+		{
+			if c.Indexes.SlotToBlocktime.URI.IsZero() {
+				return fmt.Errorf("indexes.slot_to_blocktime.uri must be set")
+			}
+			if err := isSupportedURI(c.Indexes.SlotToBlocktime.URI, "indexes.slot_to_blocktime.uri"); err != nil {
+				return err
+			}
+		}
 	}
 	{
 		// check that the URIs are valid
@@ -406,6 +417,9 @@ func (c *Config) Validate() error {
 				return fmt.Errorf("indexes.gsfa.uri must be a local directory")
 			}
 		}
+		if !c.Indexes.SlotToBlocktime.URI.IsValid() {
+			return fmt.Errorf("indexes.slot_to_blocktime.uri is invalid")
+		}
 	}
 	{
 		// if epoch is 0, then the genesis URI must be set:
diff --git a/epoch.go b/epoch.go
index b2414063..6f2a145d 100644
--- a/epoch.go
+++ b/epoch.go
@@ -22,6 +22,7 @@ import (
 	carv2 "github.com/ipld/go-car/v2"
 	cidlink "github.com/ipld/go-ipld-prime/linking/cid"
 	"github.com/libp2p/go-libp2p/core/peer"
+	"github.com/rpcpool/yellowstone-faithful/blocktimeindex"
 	"github.com/rpcpool/yellowstone-faithful/bucketteer"
 	"github.com/rpcpool/yellowstone-faithful/carreader"
 	deprecatedbucketter "github.com/rpcpool/yellowstone-faithful/deprecated/bucketteer"
@@ -55,6 +56,7 @@ type Epoch struct {
 	sigToCidIndex               *indexes.SigToCid_Reader
 	sigExists                   SigExistsIndex
 	gsfaReader                  *gsfa.GsfaReader
+	blocktimeindex              *blocktimeindex.Index
 	onClose                     []func() error
 	allCache                    *hugecache.Cache
 }
@@ -63,6 +65,18 @@ func (r *Epoch) GetCache() *hugecache.Cache {
 	return r.allCache
 }
 
+func (r *Epoch) GetBlocktime(slot uint64) (int64, error) {
+	if r.blocktimeindex == nil {
+		return 0, fmt.Errorf("blocktime index is not available")
+	}
+	return r.blocktimeindex.Get(slot)
+}
+
+// GetBlocktimeIndex returns the blocktime index for the epoch.
+func (r *Epoch) GetBlocktimeIndex() *blocktimeindex.Index {
+	return r.blocktimeindex
+}
+
 func (e *Epoch) Epoch() uint64 {
 	return e.epoch
 }
@@ -479,12 +493,50 @@ func NewEpochFromConfig(
 			}
 		}
 	}
+	{
+		slotToBlocktimeFile, err := openIndexStorage(
+			c.Context,
+			string(config.Indexes.SlotToBlocktime.URI),
+		)
+		if err != nil {
+			return nil, fmt.Errorf("failed to open slot-to-blocktime index file: %w", err)
+		}
+		buf, err := ReadAllFromReaderAt(slotToBlocktimeFile, uint64(blocktimeindex.DefaultIndexByteSize))
+		if err != nil {
+			return nil, fmt.Errorf("failed to read slot-to-blocktime index: %w", err)
+		}
+		blocktimeIndex, err := blocktimeindex.FromBytes(buf)
+		if err != nil {
+			return nil, fmt.Errorf("failed to decode slot-to-blocktime index: %w", err)
+		}
+		// can close the file now:
+		err = slotToBlocktimeFile.Close()
+		if err != nil {
+			return nil, fmt.Errorf("failed to close slot-to-blocktime index file: %w", err)
+		}
+		if blocktimeIndex.Epoch() != ep.Epoch() {
+			return nil, fmt.Errorf("epoch mismatch in slot-to-blocktime index: expected %d, got %d", ep.Epoch(), blocktimeIndex.Epoch())
+		}
+		ep.blocktimeindex = blocktimeIndex
+	}
 
 	ep.rootCid = lastRootCid
 
 	return ep, nil
 }
 
+func ReadAllFromReaderAt(reader io.ReaderAt, size uint64) ([]byte, error) {
+	buf := make([]byte, size)
+	n, err := reader.ReadAt(buf, 0)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read: %w", err)
+	}
+	if uint64(n) != size {
+		return nil, fmt.Errorf("failed to read all bytes: expected %d, got %d", size, n)
+	}
+	return buf, nil
+}
+
 func ParseFilecoinProviders(vs ...string) ([]peer.AddrInfo, error) {
 	providerAddrInfos := make([]peer.AddrInfo, 0, len(vs))
 
diff --git a/grpc-server.go b/grpc-server.go
index a04c2007..1baec44b 100644
--- a/grpc-server.go
+++ b/grpc-server.go
@@ -25,6 +25,7 @@ import (
 	"github.com/rpcpool/yellowstone-faithful/ipld/ipldbindcode"
 	"github.com/rpcpool/yellowstone-faithful/iplddecoders"
 	old_faithful_grpc "github.com/rpcpool/yellowstone-faithful/old-faithful-proto/old-faithful-grpc"
+	"github.com/rpcpool/yellowstone-faithful/slottools"
 	solanatxmetaparsers "github.com/rpcpool/yellowstone-faithful/solana-tx-meta-parsers"
 	"github.com/rpcpool/yellowstone-faithful/tooling"
 	"golang.org/x/sync/errgroup"
@@ -71,7 +72,7 @@ func (me *MultiEpoch) GetVersion(context.Context, *old_faithful_grpc.VersionRequ
 func (multi *MultiEpoch) GetBlock(ctx context.Context, params *old_faithful_grpc.BlockRequest) (*old_faithful_grpc.BlockResponse, error) {
 	// find the epoch that contains the requested slot
 	slot := params.Slot
-	epochNumber := CalcEpochForSlot(slot)
+	epochNumber := slottools.CalcEpochForSlot(slot)
 	epochHandler, err := multi.GetEpoch(epochNumber)
 	if err != nil {
 		return nil, status.Errorf(codes.NotFound, "Epoch %d is not available", epochNumber)
@@ -90,7 +91,7 @@ func (multi *MultiEpoch) GetBlock(ctx context.Context, params *old_faithful_grpc
 	tim.time("GetBlock")
 	{
 		prefetcherFromCar := func() error {
-			parentIsInPreviousEpoch := CalcEpochForSlot(uint64(block.Meta.Parent_slot)) != CalcEpochForSlot(slot)
+			parentIsInPreviousEpoch := slottools.CalcEpochForSlot(uint64(block.Meta.Parent_slot)) != slottools.CalcEpochForSlot(slot)
 			if slot == 0 {
 				parentIsInPreviousEpoch = true
 			}
@@ -350,7 +351,7 @@ func (multi *MultiEpoch) GetBlock(ctx context.Context, params *old_faithful_grpc
 	{
 		// get parent slot
 		parentSlot := uint64(block.Meta.Parent_slot)
-		if (parentSlot != 0 || slot == 1) && CalcEpochForSlot(parentSlot) == epochNumber {
+		if (parentSlot != 0 || slot == 1) && slottools.CalcEpochForSlot(parentSlot) == epochNumber {
 			// NOTE: if the parent is in the same epoch, we can get it from the same epoch handler as the block;
 			// otherwise, we need to get it from the previous epoch (TODO: implement this)
 			parentBlock, _, err := epochHandler.GetBlock(WithSubrapghPrefetch(ctx, false), parentSlot)
@@ -415,13 +416,15 @@ func (multi *MultiEpoch) GetTransaction(ctx context.Context, params *old_faithfu
 	}
 	response.Slot = uint64(transactionNode.Slot)
 	{
-		block, _, err := epochHandler.GetBlock(ctx, uint64(transactionNode.Slot))
-		if err != nil {
-			return nil, status.Errorf(codes.Internal, "Failed to get block: %v", err)
-		}
-		blocktime := uint64(block.Meta.Blocktime)
-		if blocktime != 0 {
+		blocktimeIndex := epochHandler.GetBlocktimeIndex()
+		if blocktimeIndex != nil {
+			blocktime, err := blocktimeIndex.Get(uint64(transactionNode.Slot))
+			if err != nil {
+				return nil, status.Errorf(codes.Internal, "Failed to get blocktime: %v", err)
+			}
 			response.BlockTime = int64(blocktime)
+		} else {
+			return nil, status.Errorf(codes.Internal, "Failed to get blocktime: blocktime index is nil")
 		}
 	}
 
@@ -606,29 +609,24 @@ func (multi *MultiEpoch) Get(ser old_faithful_grpc.OldFaithful_GetServer) error
 
 func (multi *MultiEpoch) GetBlockTime(ctx context.Context, params *old_faithful_grpc.BlockTimeRequest) (*old_faithful_grpc.BlockTimeResponse, error) {
 	slot := params.Slot
-	epochNumber := CalcEpochForSlot(slot)
+	epochNumber := slottools.CalcEpochForSlot(slot)
 	epochHandler, err := multi.GetEpoch(epochNumber)
 	if err != nil {
 		return nil, status.Errorf(codes.NotFound, "Epoch %d is not available", epochNumber)
 	}
 
-	block, _, err := epochHandler.GetBlock(WithSubrapghPrefetch(ctx, false), slot)
-	if err != nil {
-		if errors.Is(err, compactindexsized.ErrNotFound) {
-			return nil, status.Errorf(codes.NotFound, "Slot %d was skipped, or missing in long-term storage", slot)
-		} else {
+	blocktimeIndex := epochHandler.GetBlocktimeIndex()
+	if blocktimeIndex != nil {
+		blocktime, err := blocktimeIndex.Get(slot)
+		if err != nil {
 			return nil, status.Errorf(codes.Internal, "Failed to get block: %v", err)
 		}
+		return &old_faithful_grpc.BlockTimeResponse{
+			BlockTime: blocktime,
+		}, nil
+	} else {
+		return nil, status.Errorf(codes.Internal, "Failed to get block: blocktime index is not available")
 	}
-
-	blocktime := uint64(block.Meta.Blocktime)
-	if blocktime == 0 {
-		return nil, status.Errorf(codes.NotFound, "Blocktime for slot %d is not available", slot)
-	}
-
-	return &old_faithful_grpc.BlockTimeResponse{
-		BlockTime: int64(blocktime),
-	}, nil
 }
 
 func (multi *MultiEpoch) StreamBlocks(params *old_faithful_grpc.StreamBlocksRequest, ser old_faithful_grpc.OldFaithful_StreamBlocksServer) error {
@@ -827,7 +825,7 @@ func (multi *MultiEpoch) processSlotTransactions(
 				ctx,
 				pKey,
 				1000,
-				func(epochNum uint64, oas linkedlog.OffsetAndSizeAndBlocktime) (*ipldbindcode.Transaction, error) {
+				func(epochNum uint64, oas linkedlog.OffsetAndSizeAndSlot) (*ipldbindcode.Transaction, error) {
 					epoch, err := multi.GetEpoch(epochNum)
 					if err != nil {
 						return nil, fmt.Errorf("failed to get epoch %d: %w", epochNum, err)
@@ -880,7 +878,7 @@ func (multi *MultiEpoch) processSlotTransactions(
 							}
 							txResp.Slot = uint64(txn.Slot)
 
-							// To do: add blocketime after index work is done
+							// To do: add blocktime after index work is done
 						}
 
 						if err := ser.Send(txResp); err != nil {
diff --git a/gsfa/gsfa-read-multiepoch.go b/gsfa/gsfa-read-multiepoch.go
index 6141bdd3..6646136a 100644
--- a/gsfa/gsfa-read-multiepoch.go
+++ b/gsfa/gsfa-read-multiepoch.go
@@ -50,7 +50,7 @@ func (gsfa *GsfaReaderMultiepoch) Get(
 	ctx context.Context,
 	pk solana.PublicKey,
 	limit int,
-	fetcher func(uint64, linkedlog.OffsetAndSizeAndBlocktime) (*ipldbindcode.Transaction, error),
+	fetcher func(uint64, linkedlog.OffsetAndSizeAndSlot) (*ipldbindcode.Transaction, error),
 ) (EpochToTransactionObjects, error) {
 	if limit <= 0 {
 		return nil, nil
@@ -102,7 +102,7 @@ func (multi *GsfaReaderMultiepoch) GetBeforeUntil(
 	limit int,
 	before *solana.Signature, // Before this signature, exclusive (i.e. get signatures older than this signature, excluding it).
 	until *solana.Signature, // Until this signature, inclusive (i.e. stop at this signature, including it).
-	fetcher func(uint64, linkedlog.OffsetAndSizeAndBlocktime) (*ipldbindcode.Transaction, error),
+	fetcher func(uint64, linkedlog.OffsetAndSizeAndSlot) (*ipldbindcode.Transaction, error),
 ) (EpochToTransactionObjects, error) {
 	if limit <= 0 {
 		return make(EpochToTransactionObjects), nil
@@ -118,7 +118,7 @@ func (multi *GsfaReaderMultiepoch) iterBeforeUntil(
 	limit int,
 	before *solana.Signature, // Before this signature, exclusive (i.e. get signatures older than this signature, excluding it).
 	until *solana.Signature, // Until this signature, inclusive (i.e. stop at this signature, including it).
-	fetcher func(uint64, linkedlog.OffsetAndSizeAndBlocktime) (*ipldbindcode.Transaction, error),
+	fetcher func(uint64, linkedlog.OffsetAndSizeAndSlot) (*ipldbindcode.Transaction, error),
 ) (EpochToTransactionObjects, error) {
 	if limit <= 0 {
 		return make(EpochToTransactionObjects), nil
diff --git a/gsfa/gsfa-read.go b/gsfa/gsfa-read.go
index eaa01426..b3fe6219 100644
--- a/gsfa/gsfa-read.go
+++ b/gsfa/gsfa-read.go
@@ -93,9 +93,9 @@ func (index *GsfaReader) Get(
 	ctx context.Context,
 	pk solana.PublicKey,
 	limit int,
-) ([]linkedlog.OffsetAndSizeAndBlocktime, error) {
+) ([]linkedlog.OffsetAndSizeAndSlot, error) {
 	if limit <= 0 {
-		return []linkedlog.OffsetAndSizeAndBlocktime{}, nil
+		return []linkedlog.OffsetAndSizeAndSlot{}, nil
 	}
 	lastOffset, err := index.offsets.Get(pk)
 	if err != nil {
@@ -106,7 +106,7 @@ func (index *GsfaReader) Get(
 	}
 	debugln("locs.OffsetToFirst:", lastOffset)
 
-	var allTransactionLocations []linkedlog.OffsetAndSizeAndBlocktime
+	var allTransactionLocations []linkedlog.OffsetAndSizeAndSlot
 	next := lastOffset // Start from the latest, and go back in time.
 
 	for {
@@ -138,10 +138,10 @@ func (index *GsfaReader) GetBeforeUntil(
 	limit int,
 	before *solana.Signature, // Before this signature, exclusive (i.e. get signatures older than this signature, excluding it).
 	until *solana.Signature, // Until this signature, inclusive (i.e. stop at this signature, including it).
-	fetcher func(sigIndex linkedlog.OffsetAndSizeAndBlocktime) (solana.Signature, error),
-) ([]linkedlog.OffsetAndSizeAndBlocktime, error) {
+	fetcher func(sigIndex linkedlog.OffsetAndSizeAndSlot) (solana.Signature, error),
+) ([]linkedlog.OffsetAndSizeAndSlot, error) {
 	if limit <= 0 {
-		return []linkedlog.OffsetAndSizeAndBlocktime{}, nil
+		return []linkedlog.OffsetAndSizeAndSlot{}, nil
 	}
 	locs, err := index.offsets.Get(pk)
 	if err != nil {
@@ -152,7 +152,7 @@ func (index *GsfaReader) GetBeforeUntil(
 	}
 	debugln("locs.OffsetToFirst:", locs)
 
-	var allTransactionLocations []linkedlog.OffsetAndSizeAndBlocktime
+	var allTransactionLocations []linkedlog.OffsetAndSizeAndSlot
 	next := locs // Start from the latest, and go back in time.
 
 	reachedBefore := false
diff --git a/gsfa/gsfa-write.go b/gsfa/gsfa-write.go
index 136e5563..b940ecbd 100644
--- a/gsfa/gsfa-write.go
+++ b/gsfa/gsfa-write.go
@@ -28,7 +28,7 @@ type GsfaWriter struct {
 	ll                   *linkedlog.LinkedLog
 	man                  *manifest.Manifest
 	fullBufferWriterChan chan linkedlog.KeyToOffsetAndSizeAndBlocktime
-	accum                *hashmap.Map[solana.PublicKey, []*linkedlog.OffsetAndSizeAndBlocktime]
+	accum                *hashmap.Map[solana.PublicKey, []*linkedlog.OffsetAndSizeAndSlot]
 	offsetsWriter        *indexes.PubkeyToOffsetAndSize_Writer
 	ctx                  context.Context
 	cancel               context.CancelFunc
@@ -64,7 +64,7 @@ func NewGsfaWriter(
 		fullBufferWriterChan: make(chan linkedlog.KeyToOffsetAndSizeAndBlocktime, 50), // TODO: make this configurable
 		popRank:              newRollingRankOfTopPerformers(10_000),
 		offsets:              hashmap.New[solana.PublicKey, [2]uint64](int(1_000_000)),
-		accum:                hashmap.New[solana.PublicKey, []*linkedlog.OffsetAndSizeAndBlocktime](int(1_000_000)),
+		accum:                hashmap.New[solana.PublicKey, []*linkedlog.OffsetAndSizeAndSlot](int(1_000_000)),
 		ctx:                  ctx,
 		cancel:               cancel,
 		fullBufferWriterDone: make(chan struct{}),
@@ -145,16 +145,15 @@ func (a *GsfaWriter) Push(
 	offset uint64,
 	length uint64,
 	slot uint64,
-	blocktime uint64,
 	publicKeys solana.PublicKeySlice,
 ) error {
 	a.mu.Lock()
 	defer a.mu.Unlock()
 
-	oas := &linkedlog.OffsetAndSizeAndBlocktime{
-		Offset:    offset,
-		Size:      length,
-		Blocktime: blocktime,
+	oas := &linkedlog.OffsetAndSizeAndSlot{
+		Offset: offset,
+		Size:   length,
+		Slot:   slot,
 	}
 	publicKeys = publicKeys.Dedupe()
 	publicKeys.Sort()
@@ -190,7 +189,7 @@ func (a *GsfaWriter) Push(
 	for _, publicKey := range publicKeys {
 		current, ok := a.accum.Get(publicKey)
 		if !ok {
-			current = make([]*linkedlog.OffsetAndSizeAndBlocktime, 0, itemsPerBatch)
+			current = make([]*linkedlog.OffsetAndSizeAndSlot, 0, itemsPerBatch)
 			current = append(current, oas)
 			a.accum.Set(publicKey, current)
 		} else {
@@ -259,7 +258,7 @@ func (a *GsfaWriter) Close() error {
 	)
 }
 
-func (a *GsfaWriter) flushAccum(m *hashmap.Map[solana.PublicKey, []*linkedlog.OffsetAndSizeAndBlocktime]) error {
+func (a *GsfaWriter) flushAccum(m *hashmap.Map[solana.PublicKey, []*linkedlog.OffsetAndSizeAndSlot]) error {
 	keys := solana.PublicKeySlice(m.Keys())
 	keys.Sort()
 	for ii := range keys {
diff --git a/gsfa/linkedlog/linked-log.go b/gsfa/linkedlog/linked-log.go
index be7f2c6d..322700c3 100644
--- a/gsfa/linkedlog/linked-log.go
+++ b/gsfa/linkedlog/linked-log.go
@@ -111,7 +111,7 @@ func (s *LinkedLog) write(b []byte) (uint64, uint32, error) {
 const mib = 1024 * 1024
 
 // Read reads the block stored at the given offset.
-func (s *LinkedLog) Read(offset uint64) ([]OffsetAndSizeAndBlocktime, indexes.OffsetAndSize, error) {
+func (s *LinkedLog) Read(offset uint64) ([]OffsetAndSizeAndSlot, indexes.OffsetAndSize, error) {
 	lenBuf := make([]byte, binary.MaxVarintLen64)
 	_, err := s.file.ReadAt(lenBuf, int64(offset))
 	if err != nil {
@@ -130,7 +130,7 @@ func sizeOfUvarint(n uint64) int {
 	return binary.PutUvarint(make([]byte, binary.MaxVarintLen64), n)
 }
 
-func (s *LinkedLog) ReadWithSize(offset uint64, size uint64) ([]OffsetAndSizeAndBlocktime, indexes.OffsetAndSize, error) {
+func (s *LinkedLog) ReadWithSize(offset uint64, size uint64) ([]OffsetAndSizeAndSlot, indexes.OffsetAndSize, error) {
 	if size > 256*mib {
 		return nil, indexes.OffsetAndSize{}, fmt.Errorf("compacted indexes length too large: %d", size)
 	}
@@ -158,12 +158,12 @@ func (s *LinkedLog) ReadWithSize(offset uint64, size uint64) ([]OffsetAndSizeAnd
 	return sigIndexes, nextOffset, nil
 }
 
-func decompressIndexes(data []byte) ([]OffsetAndSizeAndBlocktime, error) {
+func decompressIndexes(data []byte) ([]OffsetAndSizeAndSlot, error) {
 	decompressed, err := tooling.DecompressZstd(data)
 	if err != nil {
 		return nil, fmt.Errorf("error while decompressing data: %w", err)
 	}
-	return OffsetAndSizeAndBlocktimeSliceFromBytes(decompressed)
+	return OffsetAndSizeAndSlotSliceFromBytes(decompressed)
 }
 
 type KeyToOffsetAndSizeAndBlocktimeSlice []KeyToOffsetAndSizeAndBlocktime
@@ -180,7 +180,7 @@ func (s KeyToOffsetAndSizeAndBlocktimeSlice) Has(key solana.PublicKey) bool {
 
 type KeyToOffsetAndSizeAndBlocktime struct {
 	Key    solana.PublicKey
-	Values []*OffsetAndSizeAndBlocktime
+	Values []*OffsetAndSizeAndSlot
 }
 
 func (s *LinkedLog) Put(
@@ -205,7 +205,7 @@ func (s *LinkedLog) Put(
 		if len(val.Values) == 0 {
 			continue
 		}
-		slices.Reverse[[]*OffsetAndSizeAndBlocktime](val.Values) // reverse the slice so that the most recent indexes are first
+		slices.Reverse[[]*OffsetAndSizeAndSlot](val.Values) // reverse the slice so that the most recent indexes are first
 		err := func() error {
 			encodedIndexes, err := createIndexesPayload(val.Values)
 			if err != nil {
@@ -245,7 +245,7 @@ func (s *LinkedLog) Put(
 	return uint64(previousSize), nil
 }
 
-func createIndexesPayload(indexes []*OffsetAndSizeAndBlocktime) ([]byte, error) {
+func createIndexesPayload(indexes []*OffsetAndSizeAndSlot) ([]byte, error) {
 	buf := make([]byte, 0, 9*len(indexes))
 	for _, index := range indexes {
 		buf = append(buf, index.Bytes()...)
diff --git a/gsfa/linkedlog/offset-size-blocktime.go b/gsfa/linkedlog/offset-size-slot.go
similarity index 60%
rename from gsfa/linkedlog/offset-size-blocktime.go
rename to gsfa/linkedlog/offset-size-slot.go
index 5e5977cb..dbf62885 100644
--- a/gsfa/linkedlog/offset-size-blocktime.go
+++ b/gsfa/linkedlog/offset-size-slot.go
@@ -8,32 +8,32 @@ import (
 	"slices"
 )
 
-func NewOffsetAndSizeAndBlocktime(offset uint64, size uint64, blocktime uint64) *OffsetAndSizeAndBlocktime {
-	return &OffsetAndSizeAndBlocktime{
-		Offset:    offset,
-		Size:      size,
-		Blocktime: blocktime,
+func NewOffsetAndSizeAndSlot(offset uint64, size uint64, slot uint64) *OffsetAndSizeAndSlot {
+	return &OffsetAndSizeAndSlot{
+		Offset: offset,
+		Size:   size,
+		Slot:   slot,
 	}
 }
 
-type OffsetAndSizeAndBlocktime struct {
-	Offset    uint64 // uint48, 6 bytes, max 281.5 TB (terabytes)
-	Size      uint64 // uint24, 3 bytes, max 16.7 MB (megabytes)
-	Blocktime uint64 // uint40, 5 bytes, max 1099511627775 (seconds since epoch)
+type OffsetAndSizeAndSlot struct {
+	Offset uint64 // encoded as uvarint
+	Size   uint64 // encoded as uvarint
+	Slot   uint64 // encoded as uvarint
 }
 
 // Bytes returns the offset and size as a byte slice.
-func (oas OffsetAndSizeAndBlocktime) Bytes() []byte {
+func (oas OffsetAndSizeAndSlot) Bytes() []byte {
 	buf := make([]byte, 0, binary.MaxVarintLen64*3)
 	buf = binary.AppendUvarint(buf, oas.Offset)
 	buf = binary.AppendUvarint(buf, oas.Size)
-	buf = binary.AppendUvarint(buf, oas.Blocktime)
+	buf = binary.AppendUvarint(buf, oas.Slot)
 	buf = slices.Clip(buf)
 	return buf
 }
 
 // FromBytes parses the offset and size from a byte slice.
-func (oas *OffsetAndSizeAndBlocktime) FromBytes(buf []byte) error {
+func (oas *OffsetAndSizeAndSlot) FromBytes(buf []byte) error {
 	if len(buf) > binary.MaxVarintLen64*3 {
 		return errors.New("invalid byte slice length")
 	}
@@ -48,14 +48,14 @@ func (oas *OffsetAndSizeAndBlocktime) FromBytes(buf []byte) error {
 		return errors.New("failed to parse size")
 	}
 	buf = buf[n:]
-	oas.Blocktime, n = binary.Uvarint(buf)
+	oas.Slot, n = binary.Uvarint(buf)
 	if n <= 0 {
-		return errors.New("failed to parse blocktime")
+		return errors.New("failed to parse slot")
 	}
 	return nil
 }
 
-func (oas *OffsetAndSizeAndBlocktime) FromReader(r UvarintReader) error {
+func (oas *OffsetAndSizeAndSlot) FromReader(r UvarintReader) error {
 	var err error
 	oas.Offset, err = r.ReadUvarint()
 	if err != nil {
@@ -65,9 +65,9 @@ func (oas *OffsetAndSizeAndBlocktime) FromReader(r UvarintReader) error {
 	if err != nil {
 		return fmt.Errorf("failed to read size: %w", err)
 	}
-	oas.Blocktime, err = r.ReadUvarint()
+	oas.Slot, err = r.ReadUvarint()
 	if err != nil {
-		return fmt.Errorf("failed to read blocktime: %w", err)
+		return fmt.Errorf("failed to read slot: %w", err)
 	}
 	return nil
 }
@@ -92,11 +92,11 @@ func (r *uvarintReader) ReadUvarint() (uint64, error) {
 	return v, nil
 }
 
-func OffsetAndSizeAndBlocktimeSliceFromBytes(buf []byte) ([]OffsetAndSizeAndBlocktime, error) {
+func OffsetAndSizeAndSlotSliceFromBytes(buf []byte) ([]OffsetAndSizeAndSlot, error) {
 	r := &uvarintReader{buf: buf}
-	oass := make([]OffsetAndSizeAndBlocktime, 0)
+	oass := make([]OffsetAndSizeAndSlot, 0)
 	for {
-		oas := OffsetAndSizeAndBlocktime{}
+		oas := OffsetAndSizeAndSlot{}
 		err := oas.FromReader(r)
 		if err != nil {
 			if errors.Is(err, io.EOF) {
diff --git a/gsfa/linkedlog/offset-size-blocktime_test.go b/gsfa/linkedlog/offset-size-slot_test.go
similarity index 59%
rename from gsfa/linkedlog/offset-size-blocktime_test.go
rename to gsfa/linkedlog/offset-size-slot_test.go
index 99d1ac6a..2d9253fc 100644
--- a/gsfa/linkedlog/offset-size-blocktime_test.go
+++ b/gsfa/linkedlog/offset-size-slot_test.go
@@ -6,17 +6,17 @@ import (
 	"testing"
 )
 
-func TestOffsetAndSizeAndBlocktime(t *testing.T) {
+func TestOffsetAndSizeAndSlot(t *testing.T) {
 	{
-		ca := OffsetAndSizeAndBlocktime{
-			Offset:    1,
-			Size:      2,
-			Blocktime: 3,
+		ca := OffsetAndSizeAndSlot{
+			Offset: 1,
+			Size:   2,
+			Slot:   3,
 		}
 		buf := ca.Bytes()
 
 		{
-			ca2 := OffsetAndSizeAndBlocktime{}
+			ca2 := OffsetAndSizeAndSlot{}
 			err := ca2.FromBytes(buf)
 			if err != nil {
 				panic(err)
@@ -28,15 +28,15 @@ func TestOffsetAndSizeAndBlocktime(t *testing.T) {
 	}
 	{
 		// now with very high values
-		ca := OffsetAndSizeAndBlocktime{
-			Offset:    281474976710655,
-			Size:      16777215,
-			Blocktime: 1099511627775,
+		ca := OffsetAndSizeAndSlot{
+			Offset: 281474976710655,
+			Size:   16777215,
+			Slot:   1099511627775,
 		}
 		buf := ca.Bytes()
 
 		{
-			ca2 := OffsetAndSizeAndBlocktime{}
+			ca2 := OffsetAndSizeAndSlot{}
 			err := ca2.FromBytes(buf)
 			if err != nil {
 				panic(err)
@@ -47,21 +47,21 @@ func TestOffsetAndSizeAndBlocktime(t *testing.T) {
 		}
 	}
 	{
-		many := []OffsetAndSizeAndBlocktime{
+		many := []OffsetAndSizeAndSlot{
 			{
-				Offset:    1,
-				Size:      2,
-				Blocktime: 3,
+				Offset: 1,
+				Size:   2,
+				Slot:   3,
 			},
 			{
-				Offset:    4,
-				Size:      5,
-				Blocktime: 6,
+				Offset: 4,
+				Size:   5,
+				Slot:   6,
 			},
 			{
-				Offset:    281474976710655,
-				Size:      16777215,
-				Blocktime: 1099511627775,
+				Offset: 281474976710655,
+				Size:   16777215,
+				Slot:   1099511627775,
 			},
 		}
 		buf := make([]byte, 0, binary.MaxVarintLen64*3*len(many))
@@ -70,7 +70,7 @@ func TestOffsetAndSizeAndBlocktime(t *testing.T) {
 		}
 
 		{
-			many2, err := OffsetAndSizeAndBlocktimeSliceFromBytes(buf)
+			many2, err := OffsetAndSizeAndSlotSliceFromBytes(buf)
 			if err != nil {
 				panic(err)
 			}
diff --git a/gsfa/manifest/manifest.go b/gsfa/manifest/manifest.go
index 96bf4a03..fe74bcf6 100644
--- a/gsfa/manifest/manifest.go
+++ b/gsfa/manifest/manifest.go
@@ -19,8 +19,12 @@ type Manifest struct {
 }
 
 var (
-	_MAGIC   = [...]byte{'g', 's', 'f', 'a', 'm', 'n', 'f', 's'}
-	_Version = uint64(3)
+	_MAGIC = [...]byte{'g', 's', 'f', 'a', 'm', 'n', 'f', 's'}
+	// NOTES:
+	// - v3: stores offset, size, and blocktime
+	// - v4: stores offset, size, and slot
+	// Version is the version of the gsfa index.
+	_Version = uint64(4)
 )
 
 var headerLenWithoutMeta = len(_MAGIC) + 8 // 8 bytes for the version
@@ -125,7 +129,7 @@ func NewManifest(filename string, meta indexmeta.Meta) (*Manifest, error) {
 			return nil, err
 		}
 		if header.Version() != _Version {
-			return nil, fmt.Errorf("unsupported manifest version: %d", header.Version())
+			return nil, fmt.Errorf("unsupported manifest version: %d; expected %d", header.Version(), _Version)
 		}
 		man.header = header
 	}
diff --git a/http-range.go b/http-range.go
index d03346fb..31170044 100644
--- a/http-range.go
+++ b/http-range.go
@@ -63,6 +63,7 @@ func (r *readCloserWrapper) ReadAt(p []byte, off int64) (n int, err error) {
 			metrics.IndexLookupHistogram.WithLabelValues(
 				indexName,
 				boolToString(r.isRemote),
+				boolToString(r.isSplitCar),
 			).Observe(float64(took.Seconds()))
 		}
 
diff --git a/index-slot-to-cid.go b/index-slot-to-cid.go
index 1161e134..67afd11f 100644
--- a/index-slot-to-cid.go
+++ b/index-slot-to-cid.go
@@ -7,11 +7,11 @@ import (
 	"path/filepath"
 	"time"
 
-	"github.com/dustin/go-humanize"
 	"github.com/ipfs/go-cid"
 	carv2 "github.com/ipld/go-car/v2"
 	"github.com/rpcpool/yellowstone-faithful/indexes"
 	"github.com/rpcpool/yellowstone-faithful/ipld/ipldbindcode"
+	"github.com/rpcpool/yellowstone-faithful/slottools"
 	"k8s.io/klog/v2"
 )
 
@@ -49,19 +49,13 @@ func CreateIndex_slot2cid(
 	}
 	rootCid := roots[0]
 
-	// TODO: use another way to precisely count the number of solana Blocks in the CAR file.
-	klog.Infof("Counting items in car file...")
-	numItems, err := carCountItems(carPath)
-	if err != nil {
-		return "", fmt.Errorf("failed to count items in car file: %w", err)
-	}
-	klog.Infof("Found %s items in car file", humanize.Comma(int64(numItems)))
-
 	tmpDir = filepath.Join(tmpDir, "index-slot-to-cid-"+time.Now().Format("20060102-150405.000000000"))
 	if err = os.MkdirAll(tmpDir, 0o755); err != nil {
 		return "", fmt.Errorf("failed to create tmp dir: %w", err)
 	}
 
+	numItems := uint64(slottools.EpochLen)
+
 	klog.Infof("Creating builder with %d items", numItems)
 	sl2c, err := indexes.NewWriter_SlotToCid(
 		epoch,
diff --git a/multiepoch-getBlock.go b/multiepoch-getBlock.go
index 11c96412..d2cd02fc 100644
--- a/multiepoch-getBlock.go
+++ b/multiepoch-getBlock.go
@@ -18,6 +18,7 @@ import (
 	jsoniter "github.com/json-iterator/go"
 	"github.com/rpcpool/yellowstone-faithful/compactindexsized"
 	"github.com/rpcpool/yellowstone-faithful/ipld/ipldbindcode"
+	"github.com/rpcpool/yellowstone-faithful/slottools"
 	solanablockrewards "github.com/rpcpool/yellowstone-faithful/solana-block-rewards"
 	"github.com/rpcpool/yellowstone-faithful/tooling"
 	"github.com/sourcegraph/jsonrpc2"
@@ -62,7 +63,7 @@ func (multi *MultiEpoch) handleGetBlock(ctx context.Context, conn *requestContex
 	slot := params.Slot
 
 	// find the epoch that contains the requested slot
-	epochNumber := CalcEpochForSlot(slot)
+	epochNumber := slottools.CalcEpochForSlot(slot)
 	epochHandler, err := multi.GetEpoch(epochNumber)
 	if err != nil {
 		return &jsonrpc2.Error{
@@ -93,7 +94,7 @@ func (multi *MultiEpoch) handleGetBlock(ctx context.Context, conn *requestContex
 	tim.time("GetBlock")
 	{
 		prefetcherFromCar := func() error {
-			parentIsInPreviousEpoch := CalcEpochForSlot(uint64(block.Meta.Parent_slot)) != CalcEpochForSlot(slot)
+			parentIsInPreviousEpoch := slottools.CalcEpochForSlot(uint64(block.Meta.Parent_slot)) != slottools.CalcEpochForSlot(slot)
 			if slot == 0 {
 				parentIsInPreviousEpoch = true
 			}
@@ -451,7 +452,7 @@ func (multi *MultiEpoch) handleGetBlock(ctx context.Context, conn *requestContex
 	{
 		// get parent slot
 		parentSlot := uint64(block.Meta.Parent_slot)
-		if (parentSlot != 0 || slot == 1) && CalcEpochForSlot(parentSlot) == epochNumber {
+		if (parentSlot != 0 || slot == 1) && slottools.CalcEpochForSlot(parentSlot) == epochNumber {
 			// NOTE: if the parent is in the same epoch, we can get it from the same epoch handler as the block;
 			// otherwise, we need to get it from the previous epoch (TODO: implement this)
 			parentBlock, _, err := epochHandler.GetBlock(WithSubrapghPrefetch(ctx, false), parentSlot)
diff --git a/multiepoch-getBlockTime.go b/multiepoch-getBlockTime.go
index c9b87172..c76ef910 100644
--- a/multiepoch-getBlockTime.go
+++ b/multiepoch-getBlockTime.go
@@ -2,10 +2,9 @@ package main
 
 import (
 	"context"
-	"errors"
 	"fmt"
 
-	"github.com/rpcpool/yellowstone-faithful/compactindexsized"
+	"github.com/rpcpool/yellowstone-faithful/slottools"
 	"github.com/sourcegraph/jsonrpc2"
 )
 
@@ -19,7 +18,7 @@ func (multi *MultiEpoch) handleGetBlockTime(ctx context.Context, conn *requestCo
 	}
 
 	// find the epoch that contains the requested slot
-	epochNumber := CalcEpochForSlot(blockNum)
+	epochNumber := slottools.CalcEpochForSlot(blockNum)
 	epochHandler, err := multi.GetEpoch(epochNumber)
 	if err != nil {
 		return &jsonrpc2.Error{
@@ -27,34 +26,35 @@ func (multi *MultiEpoch) handleGetBlockTime(ctx context.Context, conn *requestCo
 			Message: fmt.Sprintf("Epoch %d is not available", epochNumber),
 		}, fmt.Errorf("failed to get epoch %d: %w", epochNumber, err)
 	}
-
-	block, _, err := epochHandler.GetBlock(WithSubrapghPrefetch(ctx, false), blockNum)
-	if err != nil {
-		if errors.Is(err, compactindexsized.ErrNotFound) {
-			return &jsonrpc2.Error{
-				Code:    CodeNotFound,
-				Message: fmt.Sprintf("Slot %d was skipped, or missing in long-term storage", blockNum),
-			}, err
+	{
+		blocktimeIndex := epochHandler.GetBlocktimeIndex()
+		if blocktimeIndex != nil {
+			blockTime, err := blocktimeIndex.Get(blockNum)
+			if err != nil {
+				return &jsonrpc2.Error{
+					Code:    CodeNotFound,
+					Message: fmt.Sprintf("Slot %d was skipped, or missing in long-term storage", blockNum),
+				}, fmt.Errorf("failed to get blocktime: %w", err)
+			}
+			err = conn.ReplyRaw(
+				ctx,
+				req.ID,
+				func() any {
+					if blockTime != 0 {
+						return blockTime
+					}
+					return nil
+				}(),
+			)
+			if err != nil {
+				return nil, fmt.Errorf("failed to reply: %w", err)
+			}
+			return nil, nil
 		} else {
 			return &jsonrpc2.Error{
 				Code:    jsonrpc2.CodeInternalError,
 				Message: "Failed to get block",
-			}, fmt.Errorf("failed to get block: %w", err)
+			}, fmt.Errorf("failed to get blocktime: blocktime index is nil")
 		}
 	}
-	blockTime := uint64(block.Meta.Blocktime)
-	err = conn.ReplyRaw(
-		ctx,
-		req.ID,
-		func() any {
-			if blockTime != 0 {
-				return blockTime
-			}
-			return nil
-		}(),
-	)
-	if err != nil {
-		return nil, fmt.Errorf("failed to reply: %w", err)
-	}
-	return nil, nil
 }
diff --git a/multiepoch-getSignaturesForAddress.go b/multiepoch-getSignaturesForAddress.go
index d953ed9c..b9c47d5e 100644
--- a/multiepoch-getSignaturesForAddress.go
+++ b/multiepoch-getSignaturesForAddress.go
@@ -11,6 +11,7 @@ import (
 	"github.com/rpcpool/yellowstone-faithful/indexes"
 	"github.com/rpcpool/yellowstone-faithful/ipld/ipldbindcode"
 	"github.com/rpcpool/yellowstone-faithful/iplddecoders"
+	"github.com/rpcpool/yellowstone-faithful/slottools"
 	"github.com/sourcegraph/jsonrpc2"
 	"k8s.io/klog/v2"
 )
@@ -47,12 +48,11 @@ func (ser *MultiEpoch) getGsfaReadersInEpochDescendingOrderForSlotRange(ctx cont
 	ser.mu.RLock()
 	defer ser.mu.RUnlock()
 
-	startEpoch := CalcEpochForSlot(startSlot)
-	endEpoch := CalcEpochForSlot(endSlot)
+	startEpoch := slottools.CalcEpochForSlot(startSlot)
+	endEpoch := slottools.CalcEpochForSlot(endSlot)
 
 	epochs := make([]*Epoch, 0, endEpoch-startEpoch+1)
 	for _, epoch := range ser.epochs {
-
 		if epoch.Epoch() >= startEpoch && epoch.Epoch() <= endEpoch {
 			epochs = append(epochs, epoch)
 		}
@@ -80,7 +80,6 @@ func (ser *MultiEpoch) getGsfaReadersInEpochDescendingOrderForSlotRange(ctx cont
 	}
 
 	return gsfaReaderMultiEpoch, epochNums
-
 }
 
 func countTransactions(v gsfa.EpochToTransactionObjects) int {
@@ -125,26 +124,27 @@ func (multi *MultiEpoch) handleGetSignaturesForAddress(ctx context.Context, conn
 	}
 
 	var blockTimeCache struct {
-		m  map[uint64]uint64
+		m  map[uint64]int64
 		mu sync.Mutex
 	}
-	blockTimeCache.m = make(map[uint64]uint64)
-	getBlockTime := func(slot uint64, ser *Epoch) uint64 {
-		// NOTE: this means that you have to potentially fetch 1k blocks to get the blocktime for each transaction.
-		// TODO: include blocktime into the transaction data, or in the gsfaindex.
-		// return 0
+	blockTimeCache.m = make(map[uint64]int64)
+	getBlockTime := func(slot uint64, ser *Epoch) int64 {
 		blockTimeCache.mu.Lock()
 		defer blockTimeCache.mu.Unlock()
 		if blockTime, ok := blockTimeCache.m[slot]; ok {
 			return blockTime
 		}
-		block, _, err := ser.GetBlock(ctx, slot)
-		if err != nil {
-			klog.Errorf("failed to get block time for slot %d: %v", slot, err)
-			return 0
+		blocktimeIndex := ser.GetBlocktimeIndex()
+		if blocktimeIndex != nil {
+			blocktime, err := blocktimeIndex.Get(slot)
+			if err != nil {
+				klog.Errorf("failed to get block time for slot %d: %v", slot, err)
+				return 0
+			}
+			blockTimeCache.m[slot] = blocktime
+			return blocktime
 		}
-		blockTimeCache.m[slot] = uint64(block.Meta.Blocktime)
-		return uint64(block.Meta.Blocktime)
+		return 0
 	}
 
 	// Get the transactions:
@@ -154,7 +154,7 @@ func (multi *MultiEpoch) handleGetSignaturesForAddress(ctx context.Context, conn
 		limit,
 		params.Before,
 		params.Until,
-		func(epochNum uint64, oas linkedlog.OffsetAndSizeAndBlocktime) (*ipldbindcode.Transaction, error) {
+		func(epochNum uint64, oas linkedlog.OffsetAndSizeAndSlot) (*ipldbindcode.Transaction, error) {
 			epoch, err := multi.GetEpoch(epochNum)
 			if err != nil {
 				return nil, fmt.Errorf("failed to get epoch %d: %w", epochNum, err)
@@ -170,7 +170,6 @@ func (multi *MultiEpoch) handleGetSignaturesForAddress(ctx context.Context, conn
 			if err != nil {
 				return nil, fmt.Errorf("error while decoding transaction from nodex at offset %d: %w", oas.Offset, err)
 			}
-			blockTimeCache.m[uint64(decoded.Slot)] = uint64(oas.Blocktime)
 			return decoded, nil
 		},
 	)
diff --git a/multiepoch-getTransaction.go b/multiepoch-getTransaction.go
index c0ca1f1d..eeb7c7c7 100644
--- a/multiepoch-getTransaction.go
+++ b/multiepoch-getTransaction.go
@@ -10,6 +10,8 @@ import (
 	"github.com/gagliardetto/solana-go"
 	"github.com/rpcpool/yellowstone-faithful/compactindexsized"
 	"github.com/sourcegraph/jsonrpc2"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
 	"k8s.io/klog/v2"
 )
 
@@ -172,16 +174,18 @@ func (multi *MultiEpoch) handleGetTransaction(ctx context.Context, conn *request
 
 	response.Slot = ptrToUint64(uint64(transactionNode.Slot))
 	{
-		block, _, err := epochHandler.GetBlock(ctx, uint64(transactionNode.Slot))
-		if err != nil {
+		blocktimeIndex := epochHandler.GetBlocktimeIndex()
+		if blocktimeIndex != nil {
+			blocktime, err := blocktimeIndex.Get(uint64(transactionNode.Slot))
+			if err != nil {
+				return nil, status.Errorf(codes.Internal, "Failed to get block: %v", err)
+			}
+			response.Blocktime = &blocktime
+		} else {
 			return &jsonrpc2.Error{
 				Code:    jsonrpc2.CodeInternalError,
 				Message: "Internal error",
-			}, fmt.Errorf("failed to get block: %w", err)
-		}
-		blocktime := uint64(block.Meta.Blocktime)
-		if blocktime != 0 {
-			response.Blocktime = &blocktime
+			}, fmt.Errorf("failed to get blocktime: blocktime index is not available")
 		}
 	}
 
diff --git a/parse_legacy_transaction_status_meta/v-latest/parse_legacy_transaction_status_meta_ce598c5c98e7384c104fe7f5121e32c2c5a2d2eb.go b/parse_legacy_transaction_status_meta/v-latest/parse_legacy_transaction_status_meta_ce598c5c98e7384c104fe7f5121e32c2c5a2d2eb.go
index c28fd935..b15c645b 100644
--- a/parse_legacy_transaction_status_meta/v-latest/parse_legacy_transaction_status_meta_ce598c5c98e7384c104fe7f5121e32c2c5a2d2eb.go
+++ b/parse_legacy_transaction_status_meta/v-latest/parse_legacy_transaction_status_meta_ce598c5c98e7384c104fe7f5121e32c2c5a2d2eb.go
@@ -2615,7 +2615,7 @@ func BincodeDeserializeTransactionStatusMeta(input []byte) (TransactionStatusMet
 	if err == nil && deserializer.GetBufferOffset() < uint64(len(input)) {
 		// return obj, fmt.Errorf("Some input bytes were not read")
 		// TODO: fix this
-		klog.Warningf(
+		klog.V(5).Infof(
 			"Parsed %d bytes, but input was %d bytes (%d bytes not read)",
 			deserializer.GetBufferOffset(),
 			len(input),
diff --git a/parse_legacy_transaction_status_meta/v-oldest/parse_legacy_transaction_status_meta_b7b4aa5d4d34ebf3fd338a64f4f2a5257b047bb4.go b/parse_legacy_transaction_status_meta/v-oldest/parse_legacy_transaction_status_meta_b7b4aa5d4d34ebf3fd338a64f4f2a5257b047bb4.go
index d28555ef..c496cf6d 100644
--- a/parse_legacy_transaction_status_meta/v-oldest/parse_legacy_transaction_status_meta_b7b4aa5d4d34ebf3fd338a64f4f2a5257b047bb4.go
+++ b/parse_legacy_transaction_status_meta/v-oldest/parse_legacy_transaction_status_meta_b7b4aa5d4d34ebf3fd338a64f4f2a5257b047bb4.go
@@ -1943,7 +1943,7 @@ func BincodeDeserializeTransactionStatusMeta(input []byte) (TransactionStatusMet
 	if err == nil && deserializer.GetBufferOffset() < uint64(len(input)) {
 		// return obj, fmt.Errorf("Some input bytes were not read")
 		// TODO: fix this
-		klog.Warningf(
+		klog.V(5).Infof(
 			"Parsed %d bytes, but input was %d bytes (%d bytes not read)",
 			deserializer.GetBufferOffset(),
 			len(input),
diff --git a/readasonecar/read-as-one-car.go b/readasonecar/read-as-one-car.go
index 329e7a39..cd134659 100644
--- a/readasonecar/read-as-one-car.go
+++ b/readasonecar/read-as-one-car.go
@@ -1,6 +1,7 @@
 package readasonecar
 
 import (
+	"errors"
 	"fmt"
 	"io"
 	"os"
@@ -31,24 +32,24 @@ func NewMultiReader(files ...string) (*MultiReader, error) {
 		return nil, fmt.Errorf("no files provided")
 	}
 	// check that each file exists
-	for _, file := range files {
-		if _, err := os.Stat(file); err != nil {
-			return nil, err
+	for _, fn := range files {
+		if _, err := os.Stat(fn); err != nil {
+			return nil, fmt.Errorf("file %q does not exist: %w", fn, err)
 		}
 	}
 	readers := make([]*carreader.CarReader, len(files))
 	onClose := make([]func() error, len(files))
-	for i, file := range files {
-		f, err := os.Open(file)
+	for i, fn := range files {
+		file, err := os.Open(fn)
 		if err != nil {
-			return nil, fmt.Errorf("failed to open car file %s: %w", file, err)
+			return nil, fmt.Errorf("failed to open car file %q: %w", fn, err)
 		}
-		onClose[i] = f.Close
-		r, err := carreader.New(f)
+		onClose[i] = file.Close
+		reader, err := carreader.New(file)
 		if err != nil {
-			return nil, fmt.Errorf("failed to create car reader for file %s: %w", file, err)
+			return nil, fmt.Errorf("failed to create car reader for file %q: %w", fn, err)
 		}
-		readers[i] = r
+		readers[i] = reader
 	}
 	return &MultiReader{files: files}, nil
 }
@@ -93,13 +94,16 @@ func (mr *MultiReader) NextNodeBytes() (cid.Cid, uint64, []byte, error) {
 }
 
 func (mr *MultiReader) Close() error {
-	var err error
+	var errs []error
 	for _, f := range mr.onClose {
 		if e := f(); e != nil {
-			err = e
+			errs = append(errs, e)
 		}
 	}
-	return err
+	if len(errs) == 0 {
+		return nil
+	}
+	return errors.Join(errs...)
 }
 
 func (mr *MultiReader) Files() []string {
diff --git a/slot-tools.go b/slottools/edges.go
similarity index 55%
rename from slot-tools.go
rename to slottools/edges.go
index 311c0422..79bbea87 100644
--- a/slot-tools.go
+++ b/slottools/edges.go
@@ -1,4 +1,6 @@
-package main
+package slottools
+
+import "encoding/binary"
 
 // CalcEpochForSlot returns the epoch for the given slot.
 func CalcEpochForSlot(slot uint64) uint64 {
@@ -22,3 +24,23 @@ func Uint64RangesHavePartialOverlapIncludingEdges(r1 [2]uint64, r2 [2]uint64) bo
 		return r2[1] >= r1[0]
 	}
 }
+
+// EpochForSlot returns the epoch for the given slot.
+func EpochForSlot(slot uint64) uint64 {
+	return CalcEpochForSlot(slot)
+}
+
+// EpochLimits returns the start and stop slots for the given epoch (inclusive).
+func EpochLimits(epoch uint64) (uint64, uint64) {
+	return CalcEpochLimits(epoch)
+}
+
+func Uint64ToLEBytes(v uint64) []byte {
+	buf := make([]byte, 8)
+	binary.LittleEndian.PutUint64(buf, v)
+	return buf
+}
+
+func Uint64FromLEBytes(buf []byte) uint64 {
+	return binary.LittleEndian.Uint64(buf)
+}
diff --git a/slot-tools_test.go b/slottools/edges_test.go
similarity index 99%
rename from slot-tools_test.go
rename to slottools/edges_test.go
index 92a5e399..2c622eb9 100644
--- a/slot-tools_test.go
+++ b/slottools/edges_test.go
@@ -1,4 +1,4 @@
-package main
+package slottools
 
 import (
 	"testing"
diff --git a/storage.go b/storage.go
index f706eb7f..b8469cae 100644
--- a/storage.go
+++ b/storage.go
@@ -113,7 +113,7 @@ type GetBlockResponse struct {
 
 type GetTransactionResponse struct {
 	// TODO: use same format as solana
-	Blocktime   *uint64            `json:"blockTime,omitempty"`
+	Blocktime   *int64             `json:"blockTime,omitempty"`
 	Meta        any                `json:"meta"`
 	Slot        *uint64            `json:"slot,omitempty"`
 	Transaction any                `json:"transaction"`