Build against it today
Mock Servers
Every API you push gets a hosted mock automatically, serving realistic responses straight from your schema. Share one URL with your team and consumers, and wire it into CI for contract tests — zero infrastructure to run.
Generated from your spec. Always current.
Every API you push gets a mock automatically, serving realistic responses straight from your schema. Change the spec and the mock changes with it — it never lies to whoever's building against it.
$ spec0 mock create --api orders → live at https://mock.spec0.io/acme/orders
{
"id": "o_92f1",
"status": "fulfilled",
"total": 4299
} Real behaviour, no backend.
Auto-generated examples get you moving in seconds; then shape the edges with expression rules — a 404 for a missing order, a 402 when the balance is zero, a different payload per query param. The hard cases your frontend has to handle, without waiting on the API.
Response rules
Let your agents call it.
Point Claude, Cursor, or any MCP client at the mock and let them build and test integrations against a live endpoint before the real API exists. Spec0's MCP server hands the agent the spec; the mock answers its calls.
agent verified the happy path + the 402 on a zero balance — no backend yet.
Share one URL. Gate your CI.
One link your whole org and your consumers can hit, always current — no "spin it up locally" ritual. Then wire it into CI and run contract tests on every push, so a backward-incompatible change is caught in the PR that introduces it — not in a customer's incident channel.
spec0 mock create --api orders Open source · MIT The platform
Part of the spec0 platform
MCP Layer
Live API context for every coding agent.
API Registry
One governed home for every internal API.
Governance & Quality
Catch breaking changes before they ship.
AI Workflows
Spec-aware automation across your APIs.