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MockServer is a free, open-source tool that intercepts and controls HTTP and HTTPS traffic. Point your application at MockServer instead of a real service, define what responses to return, and verify the requests your application made. Use MockServer to:
  • Isolate dependencies — replace APIs, databases, or third-party services in tests
  • Control edge cases — simulate slow responses, errors, and unexpected payloads
  • Verify behavior — assert that your code made the right requests with the right data
  • Proxy live traffic — inspect, record, and replay real HTTP traffic

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Key features

  • HTTP and HTTPS mocking — a single port handles both protocols automatically using port unification
  • Flexible request matching — match on method, path, headers, cookies, query parameters, and body using exact values, regular expressions, XPath, or JSON Schema
  • OpenAPI support — auto-generate expectations from an OpenAPI v3 specification
  • Response templating — return dynamic responses using Mustache, Velocity, or JavaScript templates
  • Proxying and recording — forward requests to real services, record responses, and replay them later
  • Multiple deployment options — Docker, Kubernetes (Helm), Maven plugin, npm module, standalone JAR, JUnit 4/5, and Spring
  • Multiple client SDKs — Java, JavaScript, and Ruby clients, plus a REST API usable from any language
MockServer uses port unification so a single port handles HTTP, HTTPS, and SOCKS traffic. You do not need separate ports for different protocols.

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Where to go next

Quick Start

Get MockServer running and mock your first request in under 5 minutes.

Running MockServer

Deploy via Docker, Helm, Maven, npm, or as a standalone JAR.

Creating expectations

Define request matchers and response actions to control what MockServer returns.

REST API reference

Explore the full REST API for managing expectations, verification, and state.