API reference

Momento signs a file’s SHA-256 hash and returns a timestamp receipt. Keep that receipt with your file so you can check it later. Your file stays on your device; only its hash is sent to Momento.

Before you startCopy Anchor Link

Use the interactive OpenAPI reference to explore request schemas and try endpoints, or download the schema for your API client.

https://momento.mthatguy.workers.dev

No API key is required. Requests and responses use JSON. For POST requests, set Content-Type: application/json. You can call the API from a browser; cross-origin requests are allowed.

Create a timestampCopy Anchor Link

POST /api/v2/stamp

Compute your file’s SHA-256 hash locally, then send it to this endpoint. Momento adds the current server time and signs the receipt.

Request bodyCopy Anchor Link

Send only hash. Extra fields, including a timestamp, are rejected. The body may be up to 1,024 bytes.

Request exampleCopy Anchor Link

These examples timestamp the SHA-256 hash of an empty file. Replace it with your own file’s hash.

curl --fail-with-body https://momento.mthatguy.workers.dev/api/v2/stamp \
  -H 'Content-Type: application/json' \
  --data '{"hash":"e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"}' \
  --output receipt.json

ResponseCopy Anchor Link

201 Created — the complete receipt. The ID and signature below are placeholders; use the values returned by your request.

{
  "payload": {
    "version": 2,
    "hash": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
    "issuedAt": "2026-09-24T12:34:56.789Z",
    "receiptId": "<base64url-encoded 16 random bytes>",
    "keyId": "momento-v2-ml-dsa65"
  },
  "signature": "<base64url-encoded ML-DSA-65 signature>"
}

The response uses Cache-Control: no-store.

Verify a receiptCopy Anchor Link

POST /api/v2/verify

Hash the file you want to check, then send that hash with its saved receipt. Momento checks the signature and confirms that the receipt belongs to the hash you supplied.

Request bodyCopy Anchor Link

The body may be up to 8,192 bytes. Choose one receipt format and send only its documented fields.

Request exampleCopy Anchor Link

jq --arg hash 'e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855' \
  '{hash: $hash, receipt: .}' receipt.json |
  curl --fail-with-body https://momento.mthatguy.workers.dev/api/v2/verify \
    -H 'Content-Type: application/json' \
    --data-binary @-

ResponseCopy Anchor Link

{
  "valid": true,
  "hash": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
  "issuedAt": "2026-09-24T12:34:56.789Z",
  "receiptId": "<receipt ID>",
  "keyId": "momento-v2-ml-dsa65"
}

Get public keysCopy Anchor Link

GET /api/v2/keys

Fetch the public keys used to verify receipts. Match the receipt’s payload.keyId to an entry in keys.

curl --fail-with-body https://momento.mthatguy.workers.dev/api/v2/keys

{
  "algorithm": "ML-DSA-65",
  "keys": {
    "momento-v2-ml-dsa65": "<base64url-encoded raw ML-DSA-65 public key>"
  }
}

The key shown above is a placeholder. Use the actual key returned by the endpoint, or a trusted copy you saved earlier for offline verification. The response also includes metadata indexed by key ID: status (active, retired, or compromised), createdAt (or null when unknown), a lowercase SHA-256 fingerprint of raw ML-DSA-65 key bytes, and fingerprintAlgorithm: sha256-ml-dsa65-raw. All older Ed25519 keys must be discarded; v1 receipts are rejected. Future ML-DSA-65 rotation can retain uncompromised v2 verification keys. See Protocol v2.

Check service healthCopy Anchor Link

GET /api/health

Check whether the API is responding. This does not check signing configuration or rate-limit availability.

curl --fail-with-body https://momento.mthatguy.workers.dev/api/health

{ "ok": true }

Check signing readinessCopy Anchor Link

GET /api/ready

Returns 200 with { "ready": true } when the signing and verification keys pass an ML-DSA-65 self-test and the rate-limit bindings are configured. Otherwise returns 503 with { "ready": false }. Self-tests are cached up to 30 seconds per Worker isolate. This check does not consume request quota, test the rate-limit backend, or certify the server clock. Responses use Cache-Control: no-store.

The status page performs this live check. It does not report historical uptime.

ErrorsCopy Anchor Link

Request errors use an error field. They are separate from a receipt that fails verification. API responses include a generated X-Request-ID for support. Application request logs omit submitted hashes, request bodies, client IPs, and query strings.

{ "error": "invalid_hash" }

Rate limitsCopy Anchor Link

If you receive 429, wait for the Retry-After interval before trying again. People sharing an IP address share the per-client limit. The application does not rate-limit the two GET endpoints.

These are abuse controls, not guaranteed quotas: Cloudflare’s counters are local to each location and eventually consistent. The hosting plan also has a daily request ceiling. See the rate limits guide for counting rules, retry behavior, and how to stay within them.

Verify offlineCopy Anchor Link

You can verify a saved receipt without calling this API. Use a trusted copy of the public key and the original file.

1. Validate the receipt’s structure and version.
2. Select the public key identified by payload.keyId.
3. Decode the base64url signature and verify it with ML-DSA-65 over the UTF-8 bytes of the array below.
4. Compute SHA-256 over the file’s raw bytes and compare its lowercase hexadecimal digest with payload.hash.

JSON.stringify([
  'Momento timestamp receipt v2 / ML-DSA-65',
  payload.version,
  payload.hash,
  payload.issuedAt,
  payload.receiptId,
  payload.keyId,
]);

The order matters. The signature covers this array, not the serialized receipt object. File names are not signed.

The browser tool and CLI use the shared protocol implementation in packages/protocol/src/index.ts for receipt validation and offline verification. Checking the signature authenticates the receipt; comparing the file hash ties it to your file. See Trust and limits for what a Momento timestamp proves.