diff --git a/cmd-x-index-cid2subsetoffset.go b/cmd-x-index-cid2subsetoffset.go
new file mode 100644
index 00000000..216226f1
--- /dev/null
+++ b/cmd-x-index-cid2subsetoffset.go
@@ -0,0 +1,110 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"time"
+
+	"github.com/rpcpool/yellowstone-faithful/indexes"
+	"github.com/urfave/cli/v2"
+	"k8s.io/klog/v2"
+)
+
+func newCmd_Index_cid2subsetOffset() *cli.Command {
+	var verify bool
+	var epoch uint64
+	var network indexes.Network
+	var indexDir string
+	return &cli.Command{
+		Name:        "cid-to-offset",
+		Description: "Given all split CAR files corresponding to a Solana epoch, create an index of the file that maps CIDs to offsets in the CAR file.",
+		ArgsUsage:   "<car-paths> <index-dir>",
+		Before: func(c *cli.Context) error {
+			if network == "" {
+				network = indexes.NetworkMainnet
+			}
+			return nil
+		},
+		Flags: []cli.Flag{
+			&cli.BoolFlag{
+				Name:        "verify",
+				Usage:       "verify the index after creating it",
+				Destination: &verify,
+			},
+			&cli.StringFlag{
+				Name:  "tmp-dir",
+				Usage: "temporary directory to use for storing intermediate files",
+				Value: os.TempDir(),
+			},
+			&cli.Uint64Flag{
+				Name:        "epoch",
+				Usage:       "the epoch of the CAR files",
+				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
+				},
+			},
+			&cli.StringFlag{
+				Name:        "index-dir",
+				Usage:       "directory to store the index",
+				Destination: &indexDir,
+				Required:    true,
+			},
+		},
+		Subcommands: []*cli.Command{},
+		Action: func(c *cli.Context) error {
+			carPaths := c.Args().Slice()
+			tmpDir := c.String("tmp-dir")
+
+			if ok, err := isDirectory(indexDir); err != nil {
+				return err
+			} else if !ok {
+				return fmt.Errorf("index-dir is not a directory")
+			}
+
+			{
+				startedAt := time.Now()
+				defer func() {
+					klog.Infof("Finished in %s", time.Since(startedAt))
+				}()
+				klog.Infof("Creating CID-to-offset index for %s", carPath)
+				indexFilepath, err := CreateIndex_cid2offset(
+					context.TODO(),
+					epoch,
+					network,
+					tmpDir,
+					carPath,
+					indexDir,
+				)
+				if err != nil {
+					panic(err)
+				}
+				klog.Info("Index created")
+				if verify {
+					klog.Infof("Verifying index for %s located at %s", carPath, indexFilepath)
+					startedAt := time.Now()
+					defer func() {
+						klog.Infof("Finished in %s", time.Since(startedAt))
+					}()
+					err := VerifyIndex_cid2offset(context.TODO(), carPath, indexFilepath)
+					if err != nil {
+						return cli.Exit(err, 1)
+					}
+					klog.Info("Index verified")
+					return nil
+				}
+			}
+			return nil
+		},
+	}
+}
diff --git a/index-cid-to-subset-offset.go b/index-cid-to-subset-offset.go
new file mode 100644
index 00000000..55fafa90
--- /dev/null
+++ b/index-cid-to-subset-offset.go
@@ -0,0 +1,84 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"path/filepath"
+	"time"
+
+	"github.com/dustin/go-humanize"
+	"github.com/rpcpool/yellowstone-faithful/carreader"
+	"github.com/rpcpool/yellowstone-faithful/indexes"
+	"k8s.io/klog/v2"
+)
+
+func CreateIndex_cid2subsetOffset(
+	ctx context.Context,
+	epoch uint64,
+	network indexes.Network,
+	tmpDir string,
+	carPaths []string,
+	indexDir string,
+) (string, error) {
+
+	for _, carPath := range carPaths {
+		// 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)
+		}
+
+		carFile, err := os.Open(carPath)
+		if err != nil {
+			return "", fmt.Errorf("failed to open car file: %w", err)
+		}
+		defer carFile.Close()
+
+		rd, err := carreader.New(carFile)
+		if err != nil {
+			return "", fmt.Errorf("failed to create car reader: %w", err)
+		}
+		// check it has 1 root
+		if len(rd.Header.Roots) != 1 {
+			return "", fmt.Errorf("car file must have exactly 1 root, but has %d", len(rd.Header.Roots))
+		}
+
+		klog.Infof("Getting car file size")
+		targetFileSize, err := getFileSize(carPath)
+		if err != nil {
+			return "", fmt.Errorf("failed to get car file size: %w", err)
+		}
+
+		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-cid-to-subset-offset-"+time.Now().Format("20060102-150405.000000000"))
+		if err = os.MkdirAll(tmpDir, 0o755); err != nil {
+			return "", fmt.Errorf("failed to create tmp dir: %w", err)
+		}
+
+		rootCid := rd.Header.Roots[0]
+
+		klog.Infof("Creating builder with %d items and target file size %d", numItems, targetFileSize)
+		c2so, err := indexes.NewWriter_CidToSubsetOffsetAndSize(
+			epoch,
+			rootCid,
+			network,
+			tmpDir,
+			numItems,
+		)
+		if err != nil {
+			return "", fmt.Errorf("failed to open index store: %w", err)
+		}
+		defer c2so.Close()
+	}
+
+}