Mockzilla MCP

@mockzilla/mcp

MCP server for Mockzilla - an open-source API mock server for OpenAPI specifications. Let Claude Code, Claude Desktop, Cursor, or Gemini CLI install Mockzilla, inspect OpenAPI specs, and spin up realistic local mock APIs in seconds. No account required for local use.

Source: github.com/mockzilla/mockzilla-mcp

Use cases

• Local API development - mock any OpenAPI spec without a real backend or sandbox account
• CI/CD integration testing - zero external dependencies in your pipeline
• PSP and payment API mocking - Stripe, PayPal, Adyen from your editor without test accounts
• Crypto exchange API mocking - Binance, Bybit without registered accounts
• Rate limit protection - develop against OpenAI, Twilio without burning quota
• Agentic workflows - let Claude or Cursor spin up and manage mock servers automatically

Two planes

@mockzilla/mcp exposes two planes of tools to your MCP client.

Local plane (no account required)

Runs on your machine. No Mockzilla account needed.

From an agent you can:

• Check whether the Mockzilla CLI is installed, and install it into a managed cache (no changes to system PATH).
• Inspect and lint an OpenAPI spec, or scan a folder for specs.
• Simplify a spec that is too heavy to mock, or pack services into a .mockz archive.
• Generate Go code from a spec: models, a server for one of 14 routers, a client, or MCP tools.
• Serve any OpenAPI spec locally as a portable mock server, and call its endpoints.
• Mock a single HTTP endpoint without a spec.
• List, stop, and clear locally managed mocks.

Hosted plane (log in once)

Ask your agent to log in, or ask for something hosted. The agent calls the login tool, your browser opens the Mockzilla login, and you pick an organization and read-only or read-and-write access. The bridge keeps the login on your machine and renews it by itself. Hosted tools are listed from the start; before you log in, the agent is told to log in first.

Agents can then:

• List deployed sims.
• Browse catalog products.
• Deploy hosted mocks from a spec, URL, or catalog bundle.
• Wait for a deploy and return the live URL.

Before logging in, only the local plane is exposed. Agents can still help users explore Mockzilla and run local mocks before they sign up.

Example prompts

You can use these directly from Claude Code, Claude Desktop, Cursor, or Gemini CLI once mockzilla is configured as an MCP server.

Local plane (no account)

• "Is the mockzilla CLI installed on this machine?"
• "Install Mockzilla for me."
• "Spin up the Petstore OpenAPI spec locally so I can curl it."
• "What endpoints does https://example.com/openapi.yaml expose?"
• "Mock POST /checkout to return a 402 response."
• "List the mock endpoints you're managing."
• "Stop the mock server you started."
• "Generate Go models and a chi server for openapi.yml into ./api."

Hosted plane (after logging in)

• "Log me in to Mockzilla."
• "List the sims I have deployed."
• "Show me the catalog products."
• "Deploy a Stripe mock named stripe-test and give me the live URL."
• "Create a hosted mock from this OpenAPI URL on mockzilla.org."

Install

Claude Code

One-liner, no config file editing:

claude mcp add -s user mockzilla -- npx -y @mockzilla/mcp@latest

• -s user installs for your user account (available in every project).
• Drop -s user to scope to the current project only.

Claude Desktop

Edit ~/Library/Application Support/Claude/claude_desktop_config.json:

{

"mcpServers": { "mockzilla": { "command": "npx", "args": ["-y", "@mockzilla/mcp@latest"] } } }

Restart Claude Desktop after editing.

Cursor

Easiest: Settings -> MCP Servers -> Add new MCP server and fill in:

• Name: mockzilla
• Command: npx
• Args: -y @mockzilla/mcp@latest

Or edit ~/.cursor/mcp.json directly:

{

"mcpServers": { "mockzilla": { "command": "npx", "args": ["-y", "@mockzilla/mcp@latest"] } } }

Restart Cursor after editing.

Gemini CLI

One-liner, no manual JSON editing:

gemini mcp add -s user mockzilla npx -y @mockzilla/mcp@latest

• -s user writes to ~/.gemini/settings.json (available in every project).
• Drop -s user (or use -s project) to scope to the current directory's .gemini/settings.json.

Or edit the settings file directly:

{

"mcpServers": { "mockzilla": { "command": "npx", "args": ["-y", "@mockzilla/mcp@latest"] } } }

Restart the Gemini CLI after editing.

Why @latest?

Without @latest, npx caches the first resolved version and won't pick up new publishes. Pinning to @latest makes npx re-check the registry on every spawn, so a Claude / Cursor / Gemini restart is enough to upgrade. Trade-off: ~200 ms extra startup time.

Local tools

These tools are always available and never leave the user's machine.

Setup and status

• `check_cli` Resolve Mockzilla on this machine: system PATH -> bridge cache -> go run invocation. Returns install options if nothing matches.

• `install_cli` Install Mockzilla into ~/.cache/mockzilla-mcp/. Methods: download (prebuilt from GitHub releases, default), go-install, go-run. Never touches system PATH.

• `bridge_status` Report the bridge's version, check npm for newer publishes, and surface upgrade steps.

OpenAPI exploration and docs

• `info` Summarise an OpenAPI spec without serving it: {title, version, openapi_version, endpoint_count, paths}. Also reads .mockz packages.

• `lint` Find schemas in a spec that no value can satisfy, so a broken spec is caught before serving it: {clean, defect_count, defects}.

• `discover_specs` Scan a directory for OpenAPI specs and folders of static endpoint files. Returns a suggested_input for serve_locally.

• `mockzilla_docs_topics` List the Mockzilla docs, by category, with each topic's title and summary. The product docs from mockzilla.org, the engine docs and the mockzilla-codegen docs all ship inside the package, so no network or login is needed.

• `mockzilla_docs_read` Return the full markdown for one or more topics, or a whole category.

• `mockzilla_docs_search` Keyword search across all docs; returns top sections with snippets.

Reshaping specs

• `simplify` Drop or reduce union types, strip x-* extensions, and optionally cap optional properties per schema. Writes the simplified spec to disk and returns its path.

• `pack` Pack a directory of services into a .mockz archive that serve_locally can serve, even from a URL.

Generating code

• `generate` Run mockzilla generate, the built-in mockzilla-codegen: Go models from a spec, plus a server, a client or MCP tools when asked. Reads codegen.yaml when the folder has one. Writes the files, lists them first with dry_run, or reports stale ones with check, along with the spec's errors and warnings. Needs CLI 2.11.0 or newer.

Local mocking

• `serve_locally` Start a portable mock server on a free port. Accepts a spec file, directory, or public https URL. Returns {url, port, pid, services}. For a single spec, latency, errors, mount and context add delay, inject error responses, change the mount path, or set replacement values.

• `stop_locally` Stop a server started by serve_locally.

• `call_endpoint` Make an HTTP request and return {status, headers, body}, to show a mock's response. Localhost only unless allow_remote is set.

• `mock_endpoint` Quickly mock a single HTTP endpoint without an OpenAPI spec. Writes a static response into the managed mocks dir and (re)starts the shared server. Takes status and headers for a failure or a redirect with a real body (404 with an error payload, 201 with a Location); omit response for a body-less 204 or 304. Needs mockzilla 2.8.20 or newer.

• `list_mock_endpoints` List all endpoints currently mocked, plus the running server's URL and the Mockzilla UI URL.

• `clear_mock_endpoints` Wipe all mocks and stop the managed server.

• `request_history` List the requests the running server answered: method, URL, status, content type, latency, and whether the response came from an upstream. Pass id with service for one request's full headers and body. Reads the server's own history API, so no account is needed.

• `diagnose_requests` Explain what is wrong with the recorded traffic and where its data came from: a breakdown by origin, status and content type, latency p50/p95/max, and findings such as an upstream that failed and silently fell back to a generated mock, a 404 from a wrong mount prefix, or a JSON body under a non-JSON content type.

• `setup_replay` Configure replay for a service: record a response once, then serve it back for every matching request. Returns recording_scope saying what each endpoint is keyed by, since with no match fields every call to an endpoint shares one recording. Writes config.yml only inside the bridge's own mocks dir; for a folder from your own project it returns the YAML and where it goes.

• `list_replays` List a service's recordings, with the request values each one is keyed by.

• `check_github_deployable` Say whether a repository or folder would deploy a mock, and what is missing if not. Knows both kinds: portable service folders and a codegen Go server. Read-only.

• `list_github_repos` The user's repositories, flagging which already publish mocks, so the agent can ask which one to use.

• `publish_to_github` Push mocks to one of the user's own repositories and let the Mockzilla action deploy them at a host of their own, https:// .api.mockz.io. The label is the repository name, with -2, -3 if it is taken. No Mockzilla account needed: the first push registers the repository. Merges into an existing services folder rather than replacing it, and never overwrites an existing workflow.

• `wait_for_github_deploy` Wait for the workflow run and return the live URL, as the action reported it.

• `unpublish_from_github` Take the mocks down and free the simulation slot, optionally deleting the repository too.

Account

• `login` Opens the Mockzilla login in the browser, where the user picks an organization and read-only or read-and-write access. Returns right away with the login link. The agent calls a hosted tool again once the user approves. The login is saved under ~/.config/mockzilla-mcp/, one per server URL, and renewed automatically.

• `logout` Revokes the connection and deletes the saved login. Log out and in again to switch organization or access.

Hosted tools

@mockzilla/mcp lists the hosted tools from the start and forwards them to mockzilla.org's MCP endpoint once you log in. At the time of writing, the hosted surface includes:

• get_context
• list_sims
• list_catalog_products
• deploy_mock_from_catalog
• deploy_mock_from_spec
• deploy_mock_from_url
• wait_for_deploy

Refer to the hosted server's docs or the MCP registry entry for the live tool list.

On a machine without a browser, such as CI or a remote server, set MOCKZILLA_TOKEN to an API key from the dashboard instead of logging in. The hosted tools are then available from the start.

Configuration

| MOCKZILLA_NO_BROWSER | unset | Set to 1 to not open a browser on login; the agent shows the link i