diff --git a/.gitignore b/.gitignore
index 43c633a..dd05106 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,6 +4,9 @@
 /build
 /webui/dist
 
+# test fixtures
+*.temp.jsonl
+
 # dependencies
 node_modules/
 npm-debug.log*
diff --git a/src/data/StatsFileSource.ts b/src/data/StatsFileSource.ts
index 39bf802..a003a48 100644
--- a/src/data/StatsFileSource.ts
+++ b/src/data/StatsFileSource.ts
@@ -1,7 +1,7 @@
 import assert from 'assert';
 
 import type { PartialStatsEntry, StatsEntry, StatsSource } from './types';
-import { appendJsonLine, forEachJsonLines, parseJsonLine } from '../utils/ndjson';
+import { appendJsonLine, forEachJsonLines, parseJsonLine } from '../utils/jsonl';
 
 export class StatsFileSource implements StatsSource {
   constructor(public readonly statsPath: string) {
diff --git a/src/utils/__tests__/fixtures/ndjson.json b/src/utils/__tests__/fixtures/specification.jsonl
similarity index 100%
rename from src/utils/__tests__/fixtures/ndjson.json
rename to src/utils/__tests__/fixtures/specification.jsonl
diff --git a/src/utils/__tests__/jsonl.test.ts b/src/utils/__tests__/jsonl.test.ts
new file mode 100644
index 0000000..448909d
--- /dev/null
+++ b/src/utils/__tests__/jsonl.test.ts
@@ -0,0 +1,91 @@
+import { describe, expect, it, mock } from 'bun:test';
+import fs from 'fs';
+import path from 'path';
+
+import { appendJsonLine, forEachJsonLines, parseJsonLine } from '../jsonl';
+
+describe('forEachJsonLines', () => {
+  it('iterates each line of file', async () => {
+    const lines: string[] = [];
+    await forEachJsonLines(fixture('specification'), (content) => {
+      lines.push(content);
+    });
+
+    expect(lines).toEqual([
+      expect.stringContaining('Gilbert'),
+      expect.stringContaining('Alexa'),
+      expect.stringContaining('May'),
+      expect.stringContaining('Deloise'),
+    ]);
+  });
+
+  it('iterates each line with line numbers starting from 1', async () => {
+    const onReadLine = mock();
+    await forEachJsonLines(fixture('specification'), onReadLine);
+
+    // Callback is invoked with (content, line, reader) => ...
+    expect(onReadLine).not.toHaveBeenCalledWith(expect.any(String), 0, expect.any(Object));
+    expect(onReadLine).toHaveBeenCalledWith(expect.any(String), 1, expect.any(Object));
+    expect(onReadLine).toHaveBeenCalledWith(expect.any(String), 2, expect.any(Object));
+    expect(onReadLine).toHaveBeenCalledWith(expect.any(String), 3, expect.any(Object));
+    expect(onReadLine).toHaveBeenCalledWith(expect.any(String), 4, expect.any(Object));
+  });
+});
+
+describe('parseJsonLine', () => {
+  it('parses a single line from file', async () => {
+    expect(await parseJsonLine(fixture('specification'), 1)).toMatchObject({ name: 'Gilbert' });
+    expect(await parseJsonLine(fixture('specification'), 2)).toMatchObject({ name: 'Alexa' });
+    expect(await parseJsonLine(fixture('specification'), 3)).toMatchObject({ name: 'May' });
+    expect(await parseJsonLine(fixture('specification'), 4)).toMatchObject({ name: 'Deloise' });
+  });
+
+  it('throws if single line is not found', async () => {
+    await expect(parseJsonLine(fixture('specification'), 99999)).rejects.toThrow(
+      'Line 99999 not found in file'
+    );
+  });
+});
+
+describe('appendJsonLine', () => {
+  it('appends a single line to file', async () => {
+    const file = fixture('append-single', { temporary: true });
+    await appendJsonLine(file, { name: 'Gilbert' });
+    await expect(fs.promises.readFile(file, 'utf-8')).resolves.toBe('{"name":"Gilbert"}\n');
+  });
+
+  it('appends multiple lines to file', async () => {
+    const file = fixture('append-multiple', { temporary: true });
+    const data = [
+      { name: 'Gilbert', list: ['some-list'] },
+      { name: 'Alexa', nested: { nested: true, list: ['other', 'items'] } },
+      { name: 'May', names: 1 },
+      { name: 'Deloise', simple: true },
+    ];
+
+    for (const item of data) {
+      await appendJsonLine(file, item);
+    }
+
+    await expect(fs.promises.readFile(file, 'utf-8')).resolves.toBe(
+      data.map((item) => JSON.stringify(item) + '\n').join('')
+    );
+  });
+});
+
+/**
+ * Get the file path to a fixture, by name.
+ * This automatically adds the required `.jsonl` or `.temp.jsonl` extension.
+ * Use `temporary: true` to keep it out of the repository, and reset the content automatically.
+ */
+function fixture(name: string, { temporary = false }: { temporary?: boolean } = {}) {
+  const file = temporary
+    ? path.join(__dirname, 'fixtures', `${name}.temp.jsonl`)
+    : path.join(__dirname, 'fixtures', `${name}.jsonl`);
+
+  if (temporary) {
+    fs.writeFileSync(file, '');
+  }
+
+  return file;
+}
diff --git a/src/utils/__tests__/ndjson.test.ts b/src/utils/__tests__/ndjson.test.ts
deleted file mode 100644
index a4251db..0000000
--- a/src/utils/__tests__/ndjson.test.ts
+++ /dev/null
@@ -1,51 +0,0 @@
-import { describe, expect, it, mock } from 'bun:test';
-import path from 'path';
-
-import { forEachJsonLines, parseJsonLine } from '../ndjson';
-
-function fixture(...filePath: string[]) {
-  return path.join(__dirname, 'fixtures', ...filePath);
-}
-
-describe('forEachJsonLines', () => {
-  it('iterates each line of file', async () => {
-    const lines: string[] = [];
-    await forEachJsonLines(fixture('ndjson.json'), (content) => {
-      lines.push(content);
-    });
-
-    expect(lines).toEqual([
-      expect.stringContaining('Gilbert'),
-      expect.stringContaining('Alexa'),
-      expect.stringContaining('May'),
-      expect.stringContaining('Deloise'),
-    ]);
-  });
-
-  it('iterates each line with line numbers starting from 1', async () => {
-    const onReadLine = mock();
-    await forEachJsonLines(fixture('ndjson.json'), onReadLine);
-
-    // Callback is invoked with (content, line, reader) => ...
-    expect(onReadLine).not.toHaveBeenCalledWith(expect.any(String), 0, expect.any(Object));
-    expect(onReadLine).toHaveBeenCalledWith(expect.any(String), 1, expect.any(Object));
-    expect(onReadLine).toHaveBeenCalledWith(expect.any(String), 2, expect.any(Object));
-    expect(onReadLine).toHaveBeenCalledWith(expect.any(String), 3, expect.any(Object));
-    expect(onReadLine).toHaveBeenCalledWith(expect.any(String), 4, expect.any(Object));
-  });
-});
-
-describe('parseJsonLine', () => {
-  it('parses a single line from file', async () => {
-    expect(await parseJsonLine(fixture('ndjson.json'), 1)).toMatchObject({ name: 'Gilbert' });
-    expect(await parseJsonLine(fixture('ndjson.json'), 2)).toMatchObject({ name: 'Alexa' });
-    expect(await parseJsonLine(fixture('ndjson.json'), 3)).toMatchObject({ name: 'May' });
-    expect(await parseJsonLine(fixture('ndjson.json'), 4)).toMatchObject({ name: 'Deloise' });
-  });
-
-  it('throws if single line is not found', async () => {
-    await expect(parseJsonLine(fixture('ndjson.json'), 99999)).rejects.toThrow(
-      'Line 99999 not found in file'
-    );
-  });
-});
diff --git a/src/utils/ndjson.ts b/src/utils/jsonl.ts
similarity index 100%
rename from src/utils/ndjson.ts
rename to src/utils/jsonl.ts
diff --git a/src/utils/stats.ts b/src/utils/stats.ts
index 8a32f20..f5dddd3 100644
--- a/src/utils/stats.ts
+++ b/src/utils/stats.ts
@@ -4,7 +4,7 @@ import path from 'path';
 import { name, version } from '../../package.json';
 import { env } from '../utils/env';
 import { AtlasValidationError } from '../utils/errors';
-import { parseJsonLine } from '../utils/ndjson';
+import { parseJsonLine } from './jsonl';
 
 export type StatsMetadata = { name: string; version: string };