flaky.

A mock REST API that fails on purpose.

Real-looking data at real URLs, like every other fake API. The difference: you decide how it behaves. Force a 503, add two seconds of latency, make a third of requests fail — on any endpoint, from the query string.

Try it

GET

_delay _status _fail_rate

status — time — tier — remaining —

Press Send.

The three parameters

They work on every endpoint, including nested routes and sandboxes. Combine them freely.

# a slow endpoint — test your loading state
GET /v1/posts?_delay=3000

# a hard failure — test your error boundary
GET /v1/posts?_status=503

# an intermittent one — test your retry logic
GET /v1/posts?_fail_rate=0.3

# slow AND flaky, because that is what production is
GET /v1/products?_delay=1500&_fail_rate=0.2

This is the part you would otherwise write a local mock server for. Here it is a query parameter, so it works from a browser console, a curl one-liner, a CodePen, or a colleague's machine with nothing installed.

Resources

Resource	Rows	Nested
Loading…

Filtering, search, sorting, paging

GET /v1/todos?userId=3&completed=true   # filter by any field
GET /v1/posts?_q=voluptate                # full-text search
GET /v1/products?_sort=price&_order=desc  # sort
GET /v1/photos?_page=2&_limit=50          # paginate
GET /v1/posts/1/comments                  # nested

Writes that actually stick

POST, PUT, PATCH and DELETE are echoed, not stored — same as every other mock API, and the response says so in an x-mock-write header so nobody loses an afternoon to it. When you need writes that persist, take a sandbox.

# 1. a free key (no confirmation email)
curl -X POST https://flaky.dev/v1/keys \
  -H 'content-type: application/json' \
  -d '{"email":"you@example.com"}'

# 2. a sandbox — your own writable copy, 24 hours
curl -X POST https://flaky.dev/v1/sandbox \
  -H 'authorization: Bearer flk_...'

# 3. write to it. this one is real.
curl -X POST https://flaky.dev/v1/sandbox/<id>/posts \
  -H 'content-type: application/json' \
  -d '{"title":"this persists"}'

A sandbox is an overlay, not a copy — only records you change are stored, so the shared dataset stays cached at the edge and your sandbox stays fast.

Limits

Tier	Requests/day	Max page	Sandboxes
Anonymous	1,000	100	—
Free key	10,000	250	1
Pro	1,000,000	1,000	25

Limits reset at 00:00 UTC. Every response carries x-ratelimit-remaining. Machine-readable description of all of this at /v1/meta.