jestjs/jest · error · Error

Snapshot keys must end with a number.

Error message

Snapshot keys must end with a number.

What it means

Thrown by `keyToTestName` in @jest/snapshot-utils (utils.ts:125-128) when a snapshot file key does not end with ` <number>`. Every snapshot key is built by `testNameToKey` as `${normalizedTestName} ${count}` (utils.ts:122-123); the trailing count is what lets `keyToTestName` reverse the mapping. A key without it means the snapshot file is corrupt or hand-edited.

Source

Thrown at packages/jest-snapshot-utils/src/utils.ts:127

  key.replaceAll(/\\r\\n|\\r|\\n/g, match => {
    switch (match) {
      case '\\r\\n':
        return '\r\n';
      case '\\r':
        return '\r';
      case '\\n':
        return '\n';
      default:
        return match;
    }
  });

export const testNameToKey = (testName: string, count: number): string =>
  `${normalizeTestNameForKey(testName)} ${count}`;

export const keyToTestName = (key: string): string => {
  if (!/ \d+$/.test(key)) {
    throw new Error('Snapshot keys must end with a number.');
  }
  const testNameWithoutCount = key.replace(/ \d+$/, '');
  return denormalizeTestNameFromKey(testNameWithoutCount);
};

export const getSnapshotData = (
  snapshotPath: string,
  update: Config.SnapshotUpdateState,
): {
  data: SnapshotData;
  dirty: boolean;
} => {
  const data = Object.create(null);
  let snapshotContents = '';
  let dirty = false;

  if (fs.existsSync(snapshotPath)) {
    try {

View on GitHub (pinned to f49721c78e)

Solutions

1. Delete the offending snapshot file and re-run with `--ci=false` (or `-u`) so Jest regenerates valid keys.
2. Fix the key by appending ` <n>` (e.g. `'my test' 1`) if you must edit by hand.
3. Stop hand-editing `*.snap` files; treat them as generated artifacts.

Example fix

// before — snapshots/my.test.snap
exports['my test'] = `"value"`;

// after
exports['my test 1'] = `"value"`;

function isKeyValid(key: string): boolean {
  return / \d+$/.test(key);
}
Object.keys(snapshotData).forEach(k => {
  if (!isKeyValid(k)) throw new Error(`Corrupt snapshot key: ${k}`);
});

function isValidSnapshotKey(key: unknown): key is string {
  return typeof key === 'string' && / \d+$/.test(key);
}

try {
  keyToTestName(k);
} catch (e) {
  if (e instanceof Error && e.message === 'Snapshot keys must end with a number.') {
    // delete the snapshot file and regenerate with -u
  } else throw e;
}

When it happens

Trigger: A `*.snap` file with a key like `exports['my test'] = ...` (missing the trailing ` 1`). Calling `keyToTestName('badKey')` directly. Snapshot files written by non-Jest tooling.

Common situations: Manual edits to `*.snap` files. Merge conflicts in snapshots that dropped the count. Custom serializers/reporters that wrote keys incorrectly.

Related errors

• ${matcherHint(...)} Expected properties must be an object ${
• ${matcherHint(...)} Expected properties must be an object ${
• ${matcherHint(...)} Inline snapshot must be a string ${print
• ${matcherHintFromConfig(...)} Snapshot matchers cannot be u
• ${matcherHintFromConfig(...)} Snapshot state must be initia

AI-assisted analysis of jestjs/jest@f49721c78e (2026-08-03). Data as JSON: /data/errors/f65b20dadb390acc.json. Report an issue: GitHub.