MockServer is a highly sophisticated, multi-protocol HTTP(S) mock server and proxy for testing, written in Java with Netty. It supports HTTP/1.1, HTTP/2, HTTP/3 (QUIC), gRPC, WebSockets, DNS, TCP, and binary protocols on a single port. The core engine provides expectation-based request matching, response generation, forwarding, proxying, recording, verification, and chaos engineering (latency, connection drops, error injection). It also includes built-in LLM mocking (OpenAI, Anthropic, Gemini, etc.), OIDC/OAuth2/SAML identity providers, SCIM provisioning, WASM custom rules, and drift detection. The repository is a monorepo containing the Java server, multi-language client libraries (Java, Node, Python, Ruby, Go, .NET, Rust, PHP), a React dashboard UI, IDE plugins (JetBrains, VS Code), Helm charts, Docker images, and extensive CI/CD pipelines via Buildkite. The architecture is modular with clear separation of concerns: core model/matcher/serialization in `mockserver-core`, Netty transport in `mockserver-netty`, language-specific clients in `mockserver-client-*`, and a React UI in `mockserver-ui`. The codebase demonstrates strong engineering practices including DTO patterns with Jackson serializers, a matcher hierarchy with compiled-once validators, bounded caches, constant-time equality checks, and extensive test coverage with integration tests across multiple environments.
Mockoon is a multi-platform API mocking tool that runs mock servers locally or remotely. It is built as a monorepo with six npm packages: @mockoon/commons (shared models, migrations, OpenAPI converter), @mockoon/commons-server (core Express-based mock server engine with templating and response rules), @mockoon/app (Electron desktop application with an Angular renderer), @mockoon/cli (oclif-based command-line interface), @mockoon/cloud (cloud sync library), and the deprecated @mockoon/serverless wrapper. The architecture cleanly separates the core server logic from the delivery mechanisms. The MockoonServer class provides an HTTP/HTTPS server with a sophisticated response rule engine, a Handlebars templating system with over 100 custom helpers (including deep Faker.js integration), CRUD operations on data buckets, WebSocket support, proxy mode, and a full admin API. The desktop app uses a Redux-like state management pattern with RxJS, ensuring predictable and testable UI state transitions. The codebase demonstrates high craftsmanship in several areas. The ResponseRulesInterpreter is a self-contained DSL for matching HTTP requests to mock responses. The TemplateParser provides an extensible helper registration system. The data migration system in commons is a textbook example of handling schema evolution for JSON-based data models. The project is actively maintained with a robust CI/CD pipeline, though it carries some technical debt such as a deprecated serverless package and disabled strict TypeScript mode in the desktop app.
Microcks is a cloud-native API mocking and testing platform that ingests API specifications (OpenAPI, AsyncAPI, gRPC, GraphQL, Postman, SoapUI, HAR, and protobuf) and dynamically generates live mock endpoints and contract conformance tests. It supports REST, SOAP, GraphQL, gRPC, and asynchronous protocols (Kafka, RabbitMQ, MQTT, NATS, WebSocket, Amazon SQS/SNS, Google PubSub). The architecture consists of a main Spring Boot web application with an Angular frontend, a separate Quarkus-based async minion for event-driven mocking and testing, and optional dependencies on MongoDB, Keycloak, Kafka, and external message brokers. The system provides a rich set of features: dynamic response dispatching based on request parameters, scriptable mocks (Groovy/JavaScript), a template engine for dynamic content, SLA management, webhook notifications, AI-assisted sample generation via OpenAI, and OpenTelemetry-based observability. It is a well-engineered, modular project with extensive test coverage and a clean separation of concerns.
Stoplight Prism is an open-source HTTP mock server and validation proxy driven by OpenAPI specifications (v2, v3, v3.1) and Postman Collections. It provides two primary CLI commands: `prism mock` to simulate an API from a schema definition, and `prism proxy` to validate requests and responses against a spec while forwarding traffic to a real upstream. The architecture is a monorepo with four packages (`core`, `http`, `http-server`, `cli`) that implement a functional pipeline: route matching, input validation (body, headers, query/path parameters, security), content negotiation, and response generation (static examples or dynamic faker-generated data). It also supports callback mocking, CORS handling, and RFC 7807 problem detail errors. The codebase is written in TypeScript with heavy use of fp-ts for composable error handling and dependency injection via reader monads. While the project is mature and well-tested (unit, integration, and a text-based harness test suite), its tight coupling to Stoplight internal packages and the steep learning curve of fp-ts reduce its overall reusability for external projects. It is not a data research repository.
Stoobly Agent is a monolithic Python application that acts as a man-in-the-middle HTTP(S) proxy for recording, mocking, replaying, and testing API interactions. Built on mitmproxy, it provides a comprehensive CLI (Click-based) for managing requests, scenarios, settings, and snapshots, as well as a scaffold system that generates full Docker Compose or local development workflows. The application supports four proxy modes (record, mock, test, develop) with configurable policies, rewrite rules, and lifecycle hooks that allow custom Python callbacks at various interception stages. It persists state to a local SQLite database via an ORM with migrations, and optionally integrates with a remote Stoobly cloud service for project and scenario management. The codebase exhibits a solid architecture with adapter patterns for converting between different HTTP representations (mitmproxy, Python requests, raw, ORM, Stoobly API), factory patterns for resource creation, and builder patterns for Docker Compose generation. However, it suffers from some technical drift (deprecated mitmproxy API usage, many lazy imports, global singletons) and the test suite includes flaky end-to-end tests that depend on external services. Overall, it is a well-crafted tool for API development and testing, with several reusable components, particularly the HTTP adapter system.