Fault Injection API — free mock REST API for testing

Configure deterministic network and server failures inside your isolated sandbox.

The Fault Injection API turns failure into a setting. Configure a target — latency, a status code, a malformed body, or a flaky success rate — then call it and get exactly that. It is the catalog's tool for testing resilience deliberately instead of waiting for production to supply the outage.

Base URL: https://funapi.dev/api/faults/v1 · 5 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/faults/v1/config — Read fault profile. No token, no signup:

curl -i https://funapi.dev/api/faults/v1/config

answers 200 OK with:

{
  "latencyMs": 0,
  "status": 200,
  "malformed": false,
  "failureRate": 0
}

Open and run this endpoint

What you can practise here

Set a 50% failure rate and check that your retry policy converges instead of amplifying the load.
Inject a malformed JSON body and confirm your client reports a parse error rather than crashing.
Inject latency just above your timeout, then just below, and verify the boundary behaves as designed.
Configure a 503 with Retry-After and check your backoff honours the header instead of guessing.

control

fault profile

GET /faults/v1/config — Read fault profile · Responds with 200 Link to this endpoint
PUT /faults/v1/config — Configure fault profile (requires Bearer auth) · Responds with 200 422 Link to this endpoint
DELETE /faults/v1/config — Reset fault profile (requires Bearer auth) · Responds with 204 Link to this endpoint

target

endpoint under test

GET /faults/v1/target — Call the configured flaky target · Responds with 200 500 503 Link to this endpoint
GET /faults/v1/status/{code} — Return any status code on demand (200–599) · Responds with 200 201 202 203 204 205 206 207 300 301 302 303 304 307 308 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 421 422 423 424 425 426 428 429 431 451 500 501 502 503 504 505 507 508 511 Link to this endpoint

Auth Playground API — OAuth 2.0 flows — client credentials, auth code, refresh & expiry.
Webhooks API — Register callbacks, trigger events, inspect & replay deliveries.
Protocol Lab API — Async jobs, redirects, 503/504, JSON Patch & content negotiation.
Object Storage API — Objects, checksums, ranges & resumable uploads.

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