Protocol Lab API — free mock REST API for testing

Protocol mechanics the themed APIs do not cover: 202 Accepted with job polling, 301/302 redirects (and a chain), 503 with Retry-After, a guaranteed 504, Accept-based content negotiation with 406, HATEOAS links, RFC 6902 JSON Patch and 410 Gone.

The Protocol Lab is the catalog's HTTP semantics bench, and covers what most mock APIs never do: 202-accepted async jobs you poll to completion, 301 and 302 redirects, 503 and 504 outages, JSON Patch, and content negotiation that answers 406 when it cannot satisfy your Accept header. If a client library is going to surprise you, it will surprise you here.

Base URL: https://funapi.dev/api/protocol/v1 · 12 endpoints · OpenAPI 3.1 spec and Postman collection available. New here? Read the getting started guide.

Example request and response

GET https://funapi.dev/api/protocol/v1/moved/old-dashboard — Permanently moved — 301. No token, no signup:

curl -i https://funapi.dev/api/protocol/v1/moved/old-dashboard

answers 301 Moved Permanently with:

{
  "error": "Moved Permanently",
  "message": "The dashboard lives at /moved/new-dashboard now. Note that curl needs -L to follow redirects."
}

Open and run this endpoint

What you can practise here

• Start a job, follow the 202 and its Location header, and poll until it completes.
• Follow a 301 and a 302 and check whether your HTTP client preserves the method and the body.
• Send an Accept header the server cannot satisfy and read the 406.
• Apply a JSON Patch document, then one whose test operation fails, and compare the results.
• Trigger the 503 and 504 endpoints to confirm your timeout and retry policy behaves as designed.

jobs

202 Accepted + poll to completion

• POST /protocol/v1/jobs — Start an async job — 202 Accepted · Responds with 202 400 Link to this endpoint
• GET /protocol/v1/jobs/{id} — Poll a job — progresses on every poll · Responds with 200 404 Link to this endpoint

redirects

301, 302 and a chain to follow

• GET /protocol/v1/moved/old-dashboard — Permanently moved — 301 · Responds with 301 Link to this endpoint
• GET /protocol/v1/moved/new-dashboard — Where the 301 leads · Responds with 200 Link to this endpoint
• GET /protocol/v1/hop — A 302 redirect chain — follow it down · Responds with 200 302 400 Link to this endpoint

outages

503 & 504 on demand

• GET /protocol/v1/maintenance — Scheduled maintenance — 503 + Retry-After · Responds with 503 Link to this endpoint
• GET /protocol/v1/gateway-timeout — Slow upstream — waits ~3s, then 504 · Responds with 504 Link to this endpoint

documents

HATEOAS, JSON Patch, 406 & 410

• GET /protocol/v1/export/documents — Content negotiation via Accept (406 on anything else) · Responds with 200 406 Link to this endpoint
• GET /protocol/v1/documents — List documents (HATEOAS links) · Responds with 200 Link to this endpoint
• GET /protocol/v1/documents/{id} — Get a document (410 after deletion) · Responds with 200 404 410 Link to this endpoint
• PATCH /protocol/v1/documents/{id} — RFC 6902 JSON Patch (op/path/value) · Responds with 200 400 404 409 Link to this endpoint
• DELETE /protocol/v1/documents/{id} — Delete a document (admin only, then 410) (requires Bearer auth) · Responds with 204 401 403 404 410 Link to this endpoint

Related APIs

• Auth Playground API — OAuth 2.0 flows — client credentials, auth code, refresh & expiry.
• Webhooks API — Register callbacks, trigger events, inspect & replay deliveries.
• Object Storage API — Objects, checksums, ranges & resumable uploads.
• Modern Identity API — OIDC discovery, PKCE, device codes & token lifecycle.

All 39 mock REST APIs

Use this response elsewhere

• JSON to TypeScript on fundata.dev — an interface for this response
• JSON to Zod on fundata.dev — a runtime validator for it
• mock API data on fundata.dev — thousands of records of the same shape for your own fixtures

Last updated 2 October 2026