The independent guide to API mocking tools.

The JVM-based stub server that turns flaky third-party APIs into deterministic test fixtures.

A desktop-first mock server that gets your frontend unblocked before your coffee cools.

A heavyweight do-everything API workspace that mocks well enough — if you can live with the pricing model.

Stoplight's CLI mock server turns your spec into a validating, example-driven API in one command.

A spec-first workspace that merges API design, mocking, docs, and automated tests into a single source of truth.

A self-hosted JVM mock server that treats proxying, recording, and request verification as first-class citizens — not bolted-on extras.

An offline-first API client that stores every request as a readable file — great for reviewable collections, thin for stubbing.

A zero-install API client with real protocol breadth and a self-hostable core — but its mock server is a starter kit, not a simulator.

A fast, protocol-agnostic API client with a clean UI — and a pricing page that demands a second look.

A brutally honest look at the OpenAPI viewer every team ships, why it's still the default, and where it stops being enough.

A free hosted fake API that gets you from zero to fetching JSON in about ten seconds — and then politely runs out of road.

A human-first HTTP client that turns API poking into something you can actually read.

A heavyweight Java desktop client that refuses to die — and for WSDL-heavy estates, that's a good thing.

How to Stub a 401 Response in WireMock

Prove your client handles a slow auth failure, not just happy paths

Build Local API Mocks with Mockoon (No Code)

A mock running in under a minute, no server required

Turn an OpenAPI Spec into a Live Mock with Prism

One command from contract to running mock

Set Up Shared Team Mocks in Postman

Turn a saved example into a mock the whole team can call

Contract Testing

Contract testing verifies that a client and a service agree on the shape of their requests and responses, without running the full end-to-end system.

Record-and-Replay

Record-and-replay points a mock at a real API once, captures the traffic, then serves those captured responses offline — deterministically and without hitting the real service again.

OpenAPI Import

OpenAPI import lets a mock server generate responses straight from your OpenAPI contract, so the mock can never drift from the documented API.

Latency Simulation

Latency simulation makes a mock respond after a configurable delay, so you can test how clients behave when the real API is slow — not just when it is instant.

Fault Injection

Fault injection is the practice of deliberately breaking a mocked or real dependency—adding latency, 5xx errors, or dropped connections—to prove the system around it degrades gracefully instead of collapsing. It turns resilience from a hope into a testable property.

Fault Injection

Fault injection is the practice of deliberately breaking a mocked or real dependency—adding latency, 5xx errors, or dropped connections—to prove the system around it degrades gracefully instead of collapsing. It turns resilience from a hope into a testable property.