MockServer 
MockServer is an HTTP(S) mock server and proxy for testing. It does three things:
- Mock the APIs your application depends on, so you can develop and test against systems that are unavailable, incomplete, or hard to reproduce.
- Proxy real traffic to record, inspect, and modify requests and responses in flight — and pause them at interactive proxy breakpoints to step through, edit, or abort each exchange like a debugger for network traffic.
- Chaos engineering — make dependencies misbehave on demand, injecting latency, dropped connections, and errors to test how your application copes when the systems it relies on degrade or fail.
Speaks every protocol your stack uses. HTTP/1.1 & HTTPS, HTTP/2, gRPC & gRPC-Web, WebSockets and raw TCP are auto-detected from the first bytes of each connection, so one MockServer port handles them all with no per-protocol configuration. Beyond that core: HTTP/3 (QUIC — experimental, on its own UDP port), JSON-RPC for MCP/A2A mocking, AsyncAPI-driven message-broker testing against external Kafka and MQTT brokers, and mocked AI/LLM chat-completion APIs (OpenAI, Anthropic, Gemini, Bedrock, Azure OpenAI, Ollama).
Main Features
- Mock any API — HTTP/1.1, HTTPS, HTTP/2, HTTP/3, gRPC, gRPC-Web, JSON-RPC, WebSockets, raw TCP, and message brokers (Kafka, MQTT). Match requests on method, path, query, headers, cookies and body (JSON, XML, JSONPath, XPath, regex, OpenAPI) and return configured responses.
- Proxy & record — port forwarding, web (HTTP) proxy, HTTPS tunneling (CONNECT) and SOCKS, with full visibility of even TLS-encrypted traffic.
- Dynamic responses — response templating (Velocity, Mustache, JavaScript), class/closure callbacks and webhooks.
- OpenAPI — generate expectations directly from an OpenAPI/Swagger specification.
- Verification — assert which requests were received, in what order, and how many times.
- Chaos & resilience testing — inject latency, dropped/slow connections and failures to test how your system copes with a misbehaving dependency.
- LLM / AI mocking — mock chat-completion APIs for OpenAI, Anthropic, Gemini, Bedrock, Azure OpenAI and Ollama (including streaming), plus a built-in MCP server for AI coding assistants.
- Live dashboard — watch requests, expectations and logs in real time at
/mockserver/dashboard. - Clients & integrations — Java, JavaScript/Node, Python and Ruby clients, plus JUnit and Spring support.
- Run anywhere — Docker, Helm/Kubernetes, JAR or WAR, with optional clustered state for multi-instance deployments.
See the changelog for what has shipped in each version.
Getting started in 60 seconds
Run MockServer with Docker, then mock an endpoint and call it:
# 1. Start MockServer
docker run -d --rm -p 1080:1080 mockserver/mockserver
# 2. Mock an endpoint: GET /hello -> 200 "Hello World"
# (MockServer exposes a REST control plane on the same port)
curl -X PUT http://localhost:1080/mockserver/expectation \
-H 'Content-Type: application/json' \
-d '{
"httpRequest": { "method": "GET", "path": "/hello" },
"httpResponse": { "statusCode": 200, "body": "Hello World" }
}'
# 3. Call your mock
curl http://localhost:1080/hello
# -> Hello World
…or, on macOS / Linux, install it with Homebrew and run the mockserver command directly:
brew install mockserver
mockserver run --port 1080
One-command recipes
For common end-to-end setups, the examples/docker-compose recipes are a single docker compose up each — mock from an OpenAPI spec, a record/replay proxy, a contract-validating proxy, or a chaos proxy:
cd examples/docker-compose/mock-from-openapi
docker compose up
curl http://localhost:1080/pets
The same can be done from any client library or the dashboard at . For more configuration options see the Docker documentation.
For every way to run MockServer yourself — Docker, docker-compose recipes, the mockserver CLI, the JVM-less binary bundle, Helm/Kubernetes, the JAR, and Testcontainers — see the Self-Hosting MockServer guide.
Drive it from Postman or Bruno
Explore MockServer's REST control plane from an API client — create expectations, verify requests, and inspect recorded traffic:
- Postman — click the button above, or import
examples/postman(guide). - Bruno (open-source, git-native) — open
examples/brunoin Bruno via Open Collection (guide).
Documentation
For usage guide please see: www.mock-server.com
Developer Documentation
Architecture, code structure, infrastructure, and operations documentation is available in the docs/ directory.
AI Integration
MockServer includes a built-in MCP server for AI coding assistant integration at /mockserver/mcp. See llms.txt and AI Integration docs.
Change Log
Please see: Change Log
Community
| Discussions |  |
| Issues, Bugs & Feature Requests | |
| Roadmap | |
| Security | |
Requirements
Runtime: MockServer 6.x requires Java 17+. The minimum was raised from Java 11 as part of the Jakarta EE 10 / Spring 7 platform modernisation — see the Java 17 / Jakarta upgrade guide. If you are still on Java 11, pin to the 5.15.x line (no longer receiving security updates). The official Docker image already bundles a Java 17 runtime.
Building from source: requires JDK 17+; the produced bytecode targets Java 17.
Security Note: MockServer is a development and testing tool only. See SECURITY.md for important security considerations.
Versions
Maven Central 
Maven Central contains the following MockServer artifacts under the org.mock-server groupId. Every artifact ships in two forms — -no-dependencies (shaded, zero transitive deps, recommended) and the plain form (transitive deps declared in the POM, for the rare case where you need to override versions yourself).
Server:
- [mockserver-netty-no-dependencies](https://central.sonatyp