Open-source alternatives to Mockserver

Mockoon is an HTTP API simulation platform and design tool used to create fake API endpoints that simulate server responses without a backend. It functions as an OpenAPI mock server tool and a JSON API mocking utility, allowing for the rapid iteration of API contracts and the generation of response templates. The project distinguishes itself through a combination of stateful mocking, using a local JSON database to simulate CRUD operations, and the ability to run as a headless API mock server via a command line interface. It supports real-time collaborative editing and AI-assisted prototyping

moco is a multi-protocol mock server and programmable API stub used to simulate HTTP, REST, WebSocket, and Server-Sent Events endpoints. It enables the creation of fake backend services to facilitate development and integration testing without requiring a live server. The project distinguishes itself through its ability to act as a network traffic replay tool, capturing real request-response pairs via a proxy and playing them back locally. It also supports bidirectional communication simulations, including WebSocket server simulation and SSE stream simulation with configurable delivery delays

Mirage JS is a browser-based mock server and client-side API simulator designed for JavaScript application development. It functions as a mocking tool that intercepts network requests to simulate backend API behavior, allowing developers to build and test frontend interfaces without requiring live backend infrastructure. The tool provides a simulation layer that mimics REST endpoints to facilitate rapid prototyping of user flows and application logic. It enables the creation of fake server responses directly within the web browser to verify how an application handles various data scenarios an

Responses is a Python mocking library designed to intercept outgoing HTTP calls made with the Requests library to return predefined simulated responses. It functions as a request verification framework and a network simulation tool, allowing for the verification of application behavior against various API response patterns without making real network calls. The project distinguishes itself through a traffic recorder that captures real network interactions and saves them to files for deterministic replay. It further enables the simulation of complex network scenarios, including the triggering

Moto is a cloud service mockery framework and API mock server that simulates AWS infrastructure locally. It allows developers to test cloud-dependent code and verify infrastructure-as-code templates without deploying real resources or incurring costs. The project functions as an SDK interceptor that can patch existing service clients to redirect requests to a local mock environment. It can also be run as a standalone HTTP server, enabling any programming language to interact with the simulated endpoints. The framework covers a vast array of simulated capabilities, including data storage, com

OHHTTPStubs is an HTTP network mocking library and request interceptor used to simulate server responses for testing application behavior without a live backend. It functions as a network request stubbing tool that captures outgoing network calls and replaces them with predefined mock data, custom status codes, and headers. The library distinguishes itself through its ability to simulate a wide range of network conditions, including artificial latency and connection failures. It supports dynamic response sequencing, allowing the tool to return a series of different responses for the same requ

httplab is an HTTP mock server and interactive API simulator used to analyze incoming request payloads and simulate custom HTTP responses for application testing. It functions as a request inspector that captures and displays real-time details of HTTP headers and bodies sent by clients. The project includes a response management system that imports and stores predefined HTTP response templates using JSON files. This allows for the persistence of request and response configurations to local files for use in reusable testing scenarios. The tool provides capabilities for generating custom HTTP

Prism is a set of tools for generating mock servers and validation proxies based on OpenAPI specifications or Postman collection files. It serves as an API contract testing tool to verify that API implementations adhere to formal contracts. The project provides an OpenAPI mock server that simulates API responses and a validation proxy that checks live HTTP traffic against an OpenAPI specification to identify implementation discrepancies. It also includes a mock server capable of mimicking API behavior based on exported Postman Collection files. The tool covers API behavior simulation and tra

Proxypin is a cross-platform HTTP and HTTPS proxy debugger designed to capture, inspect, and modify network traffic. It functions as a man-in-the-middle interceptor, allowing developers to analyze application data flows and validate network communication during development and testing. The tool distinguishes itself through its focus on mobile and remote device integration, utilizing QR-code-based configuration synchronization to simplify the setup of proxy settings and security certificates. It includes an event-driven scripting engine that enables programmatic manipulation of requests and re

This library provides a utility for intercepting and simulating HTTP requests within the Axios ecosystem. It functions as an HTTP request interceptor that allows developers to define mock responses for outgoing network traffic, enabling frontend integration testing and development without requiring live backend infrastructure. The tool distinguishes itself by offering granular control over the request lifecycle, including the ability to match specific request patterns and forward unmatched traffic to actual destinations. It supports the simulation of unstable network environments by injecting

Mock is a JavaScript API mocking tool and network request interceptor designed to decouple front-end development from back-end progress. It functions as an API simulation tool and mock data generator, allowing developers to build user interfaces and high-fidelity prototypes by mimicking the request and response cycle without a live server. The system provides a mechanism for intercepting outgoing HTTP calls and returning simulated data. It enables front-end prototyping by generating synthetic datasets to validate application behavior during automated testing cycles and development. Capabilit

Orval is an OpenAPI-to-TypeScript code generator that produces fully typed API clients, data-fetching hooks, mock data, validation schemas, and server handlers from OpenAPI or Swagger specifications. It reads any YAML or JSON API specification and generates TypeScript interfaces, HTTP request functions, and framework-specific integration code that ensures compile-time correctness for all API calls. The project distinguishes itself by generating production-ready data-fetching hooks for React Query, Vue Query, Svelte Query, Solid Query, Angular, and SWR, complete with automatic cache invalidati

swagger-node is a toolkit for OpenAPI API development that ensures a project's implementation matches its documented design. It enables the generation of functional API servers and interactive documentation directly from YAML specification files. The project features a system for mapping API endpoints to specific controller functions and a mock mode that simulates API responses from the specification. This allows for API prototyping and frontend development before backend business logic is implemented. The platform provides a command-line interface for project bootstrapping, server managemen

Karate is a Gherkin API testing framework and JVM test orchestrator designed for API validation, workflow automation, and browser automation. It provides a unified environment for executing scriptable logic on the Java Virtual Machine with thread-safe concurrent processing. The project includes a built-in HTTP mock server to simulate backend API behavior by delivering dynamic responses to intercepted requests. It also features a visual regression testing tool that detects interface changes by comparing screenshots against baseline images using pixel-matching analysis. The system supports API

Webhook.site is a web-based tool that captures, inspects, and debugs incoming HTTP requests and emails sent to a unique URL, without requiring any server setup. It also functions as an API mocking and response modification tool, capable of generating mock APIs from OpenAPI specifications and altering HTTP responses, headers, and status codes for testing purposes. Beyond inspection, it serves as a platform for webhook automation and workflow orchestration, triggering multi-step automations—including database queries, SSH commands, and HTTP calls—when a webhook is received. The service distingu

Nock is a Node.js HTTP mocking library used to intercept outgoing network requests and return predefined responses. It functions as a network request interceptor and HTTP mock server, allowing developers to simulate external API behavior for automated testing without making live network calls. The project includes an API fixture recorder to capture real network interactions and save them as reusable data files for playback. It also features a network latency simulator that introduces artificial delays to outgoing HTTP responses to verify timeout handling and race conditions. The library prov

Karate is an end-to-end testing framework and API test automation tool used to validate REST and SOAP APIs, drive browser interactions, and measure system performance. It functions as a unified solution for executing automated tests across both API backends and web frontends. The framework utilizes a custom domain specific language and Gherkin-style feature mapping to define requests and assertions. It includes an API mocking server to simulate backend responses, enabling development and integration testing without live dependencies. The tool covers a broad range of functional testing catego

Moya is a network abstraction layer for Swift that provides a structured framework for defining and executing REST API requests. It functions as a type-safe API client that decouples network endpoint definitions from the underlying implementation details to prevent configuration errors and URL typos. The project distinguishes itself by using protocol-based endpoint definitions and a provider-coordinated execution model. It includes a system for mapping network responses to strongly typed objects and features a dedicated tool for generating type-safe network interface files from external REST

DoraemonKit is a mobile frontend development toolset designed to optimize the lifecycle of web and hybrid mobile applications. It functions as a comprehensive suite of productivity tools, providing specialized utilities for mobile UI inspection, web view debugging, and on-device performance monitoring. The toolset distinguishes itself through several targeted simulation and interception capabilities. It includes a network traffic interceptor for mocking API responses without modifying source code, a device state simulator for overriding GPS coordinates, and a mobile web debugging bridge that

AndroidHttpCapture is a mobile application for intercepting and analyzing HTTP and HTTPS network traffic directly on an Android device. It functions as a local proxy server and traffic interceptor to capture and monitor requests and responses from other installed mobile applications. The tool provides capabilities for MITM HTTPS decryption through root certificate installation and supports exporting captured network sessions as HAR files for external analysis. It allows for real-time response body injection and the modification of request headers via user agent spoofing. The project includes

This project is a REST API client library and Google Cloud SDK component that integrates Python applications with Google services. It functions as a discovery-based API client, utilizing an OAuth 2.0 integration library to secure requests and verify identity through access tokens and service accounts. The library is distinguished by its use of discovery documents to dynamically generate clients at runtime. By parsing JSON metadata, it maps Python method calls to HTTP requests and builds interface-based resource models that mirror the hierarchical structure of the remote service. Its broader

MSW is a JavaScript API mocking library and integration testing tool designed to intercept network requests at the network level. It allows for the definition of mock data and status codes using routing syntax to simulate server responses without requiring changes to the application source code. The project utilizes a service worker to proxy API calls in the browser, providing a mechanism for isolated frontend development and testing. It employs platform-specific network adapters to maintain a consistent mocking interface across both browser and Node.js environments. The library covers a ran

httplab is an interactive HTTP mock server, request inspection tool, and response simulator. It functions as a web server designed to capture and analyze incoming HTTP requests and headers in real time for debugging purposes. The tool enables the construction and delivery of custom HTTP responses to simulate various server behaviors. Users can forge specific headers and bodies to test how client applications handle different status codes and payloads, with the ability to save these configurations as response templates for consistent reuse across sessions. The project covers a broad surface o

Telepresence is a hybrid development environment and network proxy for Kubernetes. It provides a system for running workloads on a local machine while maintaining active connectivity to a remote cluster environment. The project functions as a traffic interceptor and network bridge, establishing a two-way tunnel between a local workstation and a remote cluster. This allows for the redirection of traffic from a remote Kubernetes service to a local process, enabling real-time debugging and testing of code without the need to redeploy containers. Its capabilities cover remote cluster connectivit

This project is a comprehensive guide and collection of best practices for testing Node.js backend applications. It provides a curated set of patterns and reference examples for writing reliable unit, integration, and component tests. The project distinguishes itself through specific strategies for backend integration, including detailed methods for API contract testing against OpenAPI specifications and shared schemas. It offers specialized guidance on managing message queue testing, focusing on idempotency, resilience, and asynchronous event synchronization. The guide covers a broad range

Mitmproxy is an interactive, programmable network proxy engine designed for traffic analysis and protocol manipulation. It functions as a gateway that intercepts, inspects, and modifies network traffic in real-time, supporting HTTP, HTTPS, WebSocket, DNS, and generic TCP or UDP streams. By acting as a trusted certificate authority, the proxy can dynamically generate and sign certificates to decrypt and analyze secure TLS-encrypted connections. The project distinguishes itself through a highly extensible, event-driven architecture that allows users to automate traffic transformation using cust