MockServer
An HTTP mocking and proxy server with request expectations, response configuration and verification APIs.
About MockServer
MockServer is a free, open-source, self-hosted tool that mocks and proxies the HTTP, HTTPS and gRPC services an application depends on. It can return configured responses for matched requests, proxy requests to a real backend while recording them, or do both at once. Its stated purpose is to let developers and testers work against controllable responses instead of real dependencies that may be unavailable or changing. The homepage describes it as running anywhere without a SaaS account.
The tool also supports verification, so a test can assert which requests the system under test sent. It can be run with a single Docker command, and the homepage shows creating an expectation through its REST API. It also includes an MCP server so AI coding assistants can control the mock and proxy.
Key features
- Mocks HTTP/1.1, HTTP/2, HTTP/3, HTTPS and gRPC services
- Records, replays and proxies traffic to a real backend
- Pauses matched or proxied requests at interactive breakpoints for inspection
- Injects latency, errors, dropped connections and malformed responses
- Declarative load scenarios with SLO verdicts, without an external load tool
- Imports OpenAPI specs, Postman collections and HAR files
Best for: Developers and test engineers who need to isolate tests from fragile or unavailable APIs and want a self-hosted, free tool.
Good for
- Free and open-source, with no SaaS account required
- Can mock, proxy and verify requests within one instance
- Includes a built-in MCP server for AI coding assistants
MockServer at a glance
- Website
- mock-server.com
- Category
- Development › APIs & Databases
- Type
- Online tool
- Pricing
- Free
- Open source
- Yes
- Last checked
- Oct 9, 2026 · Online when checked
- Listed
- Oct 9, 2026
Guides for APIs & Databases
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MockServer FAQ
How do I start MockServer quickly?
The homepage gives the command docker run -d --rm -p 1080:1080 mockserver/mockserver. After it starts, you can create an expectation with a PUT request to the /mockserver/expectation endpoint.
Can MockServer import existing API definitions?
Yes. The homepage lists importing from OpenAPI or Swagger specs, Postman collections and HAR files.
Does MockServer support mocking LLM APIs?
The homepage states that it can mock LLM and AI-provider APIs, including OpenAI, Anthropic and Bedrock, with token-by-token streaming.
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