Mock Anything

A working twin of an API, running on your machine in one command. No keys, no sandbox sign-up, no bill.

npx @shipatmidnight/mockanything stripe
# → Stripe twin running at http://localhost:4010/v1

Point your app or agent at that URL instead of the real one and it behaves like the real API for the flows it covers: create a customer, charge a test card, get the signed webhook, refund it. None of it is real, and your app's calls never reach the real provider.

Mock Anything works with most public APIs, not just a fixed list (every API in the public APIs.guru directory started as a twin in our 2026-10-29 measurement):

npx @shipatmidnight/mockanything stripe                          # a hand-tuned pack
npx @shipatmidnight/mockanything ./openapi.yaml                  # your own OpenAPI / Swagger file
npx @shipatmidnight/mockanything https://example.com/openapi.json
npx @shipatmidnight/mockanything slack                           # any name in the public APIs.guru directory (2,500+ APIs)

Why

Agents write code that calls payments, SMS, email and developer APIs all day. Testing that today means real keys (the agent can spend money or text real people), sandboxes (accounts and keys for every provider, and many regional providers barely have one), or hand-written mocks that break the moment the agent does something you didn't expect.

A twin is different from a mock:

• It keeps state. POST a customer, then GET it back. Refund a payment and the remaining balance changes. Delete something and it's gone.
• It behaves like the provider. Real ID formats, list pagination, error shapes, status lifecycles (requires_payment_method → succeeded, queued → sent → delivered).
• It sends webhooks, signed the way the provider signs them, so your verification code runs unchanged.
• It does the awkward parts: declined cards, 3-D Secure, bounced emails, undeliverable SMS, duplicate references, rate limits.
• Chaos mode (--chaos) adds timeouts, 5xx errors, 429s, slow responses, duplicate and out-of-order webhooks. Seeded, so a failure you hit can be replayed.

Built-in packs

Hand-tuned twins, checked against each provider's official SDK in our test suite.

mockanything env <pack> prints the snippet for pointing the official SDK at the twin, for example:

const stripe = new Stripe("sk_test_mockanything", { host: "localhost", port: 4010, protocol: "http" });

Any other API

Give Mock Anything an OpenAPI 3.x or Swagg

... View full README on GitHub