API development tools

Insomnia is a cross-platform API development environment that integrates a request debugger, schema design tools, a mocking server, and a test automation framework. It provides a unified workspace for sending requests and analyzing responses across REST, GraphQL, gRPC, and WebSocket protocols. The platform enables the design and preview of API specifications through a visual editor and allows for the simulation of backend behavior using mocking tools. It supports organizing and synchronizing API collections via local storage, cloud synchronization, or Git. The suite includes a command-line i

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

Tyk is an open-source API gateway written in Go that routes, secures, and monitors network traffic across REST, GraphQL, TCP, and gRPC protocols. It functions as a multi-protocol proxy designed to deliver requests to backend services while managing the end-to-end API lifecycle. The system distinguishes itself through a plugin-based architecture that allows for the injection of custom logic into the request and response middleware chain. It also features native Kubernetes integration, operating as an ingress controller that uses operators and custom resource definitions to deploy security poli

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

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

Kong is a high-performance API gateway and service connectivity platform designed to manage, secure, and monitor traffic across distributed microservices and hybrid cloud environments. It functions as a centralized control plane for service governance, providing essential traffic routing, load balancing, and request transformation capabilities to ensure consistent policy enforcement across all service endpoints. The platform distinguishes itself through a modular plugin architecture and a declarative configuration engine that allows infrastructure behavior to be defined via version-controlled

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

Easy Mock is a tool for API mocking and simulation that allows for the creation of fake server responses using schemas. It enables the generation of mock API data and the implementation of OpenAPI specifications to align development with technical contracts. The project supports collaborative API design through a shared workspace where team members can synchronize and manage mock endpoints. It also features specification-driven bootstrapping, which automatically constructs mock environments by importing standard API definition files. The system provides API development proxying to forward re

This project is an API documentation management platform and mocking server. It provides a central system for organizing API specifications and managing metadata to maintain consistency across the development lifecycle. The toolset includes a mocking engine that generates simulated backend responses, allowing frontend development to proceed without a live backend service. It also functions as a static documentation generator that converts dynamic API specifications into offline files for distribution and archival. The platform is delivered as a containerized toolset, packaging the server and

Scalar is a platform for building and managing API specifications, focusing on OpenAPI and AsyncAPI standards. It provides tools to generate interactive API references with embedded testing interfaces, create mock servers for pre-implementation testing, and build offline-first API clients that sync with backend frameworks. The platform also supports version upgrades of specifications to maintain compatibility and includes command-line utilities for local development and document management. The project distinguishes itself through automated release workflows that generate changelogs and publi

Insomnia is a desktop application designed for the design, testing, and debugging of network requests. It serves as a comprehensive environment for managing the API lifecycle, allowing users to draft interface specifications, simulate endpoints, and execute automated testing workflows within continuous integration pipelines. The platform distinguishes itself through a modular, plugin-based architecture that enables the integration of custom scripts and external tools. It supports complex development needs by providing a local-first data persistence model, environment-variable substitution for

Mockserver is a multi-protocol mock server and API verification proxy used to simulate HTTP, gRPC, and WebSocket endpoints. It functions as a tool for testing client applications without relying on live backend services, providing a system to simulate chat completions and streaming responses for large language model integrations. The project automates behavior by generating request expectations and response behaviors from OpenAPI and Swagger specification files. It differentiates itself through a network traffic simulator that introduces latency, dropped connections, and failures to verify ho

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

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

json-server is a development toolset used to simulate a full REST API from a JSON file. It functions as a customizable mock API server that allows for the simulation of CRUD operations and resource relationships without the need to write backend code. The project enables rapid prototyping by generating a fake backend that persists data changes back to a local JSON file. It distinguishes itself by providing a static asset file server to deliver local documents, images, and stylesheets alongside the mock API endpoints. The server includes capabilities for data querying, such as parameter-based

HttpRunner is a multi-protocol network testing framework designed for automating functional and regression tests of HTTP interfaces. It functions as a multi-protocol network tester supporting HTTP/1.1, HTTP/2, WebSocket, TCP, and RPC to validate diverse communication patterns. The project includes specialized engines for API performance testing, data-driven testing, and a test case generator that converts HAR files, curl commands, and Swagger definitions into executable scripts. The framework is distinguished by its ability to separate test logic from business data via a data-driven execution

WSO2 API Manager is a complete platform for building, integrating, and exposing your digital services as managed APIs in the cloud, on-premise, and hybrid architectures to drive your digital transformation strategy.

Gravitee.io - OpenSource API Management

API Platform is a headless content management system engine and framework used to build REST and GraphQL APIs. It utilizes schema-driven generation to automatically produce web endpoints based on predefined data model definitions. The platform focuses on semantic data modeling, using structured classes and ontologies to ensure information is organized for search engines and semantic web tools. It provides an automated OpenAPI specification generator and a declarative system for creating administration dashboards to manage data records without custom frontend code. The system includes capabil

Hoppscotch is an open-source API development ecosystem designed for building, testing, and debugging REST, GraphQL, and real-time APIs. It provides a unified platform that functions across web browsers, desktop applications, and command-line interfaces, allowing developers to manage the entire API lifecycle from a single environment. The platform distinguishes itself through a highly interactive, command-driven interface that utilizes a global spotlight palette and keyboard shortcuts to streamline complex workflows. It supports advanced request manipulation and validation by executing JavaScr

Bruno is a local-first API client designed for building, testing, and managing network requests across a wide range of protocols. By storing all collections and configurations as plain-text files directly on the local filesystem, it enables native version control and offline access, ensuring that project data remains under user control without requiring cloud synchronization. The platform distinguishes itself through a declarative approach to API management, utilizing a domain-specific language to define request parameters and metadata. This architecture supports a robust testing environment

Traefik is a cloud-native edge router and API gateway designed to manage service communication and traffic flow across distributed infrastructure. It functions as a dynamic service proxy that automatically discovers backend services and configures routing rules in real time, eliminating the need for manual restarts or complex configuration updates. By integrating directly with container orchestrators and service registries, it maintains a consistent state for network traffic, load balancing, and security policy enforcement. The project distinguishes itself through its deep integration with di

Swagger UI is an OpenAPI specification renderer and documentation interface that transforms JSON or YAML API definitions into a navigable, searchable website. It functions as an OpenAPI documentation UI and request client, providing a visual catalog for exploring endpoints and sending live HTTP requests to a server using a schema-defined interface. The project distinguishes itself through a plugin-based extension system and a schema-driven UI generation model. This architecture allows for the injection of custom components, state selectors, and helper functions to modify core behavior and lay

This project is a multi-protocol API simulation and mocking system designed to replace external dependencies during development and testing. It provides an API mocking server, a network traffic proxy, and specialized simulators for language model services and identity providers. The system distinguishes itself through deep AI simulation capabilities, including the emulation of language model providers and Model Context Protocol servers using JSON-RPC 2.0. It supports multi-turn conversational logic, state tracking for AI chat APIs, and the visualization of agent execution through call graphs

api-blueprint is a markdown-based API design language and specification standard used to define the structure, behavior, and data schemas of HTTP web services. It provides a formal method for mapping HTTP methods to resources and defining payload validation rules through a machine-readable syntax. The project functions as a blueprint for creating interactive technical documentation and functional mock servers. These tools transform design specifications into human-readable guides and simulated backend environments to enable integration testing before implementation. The language covers API m

Newman is a headless API client and command line tool for executing Postman collections. It serves as an API test automation tool and execution engine that allows users to run predefined sets of API requests without a graphical interface. The project differentiates itself as a data-driven testing engine, capable of iterating through request sequences using external JSON or CSV files to validate multiple sets of input values. It also functions as an API execution reporter, utilizing a plugin-based interface to output results in formats such as JSON and JUnit. The tool covers broad capability

go-swagger is a toolkit for working with Swagger/OpenAPI 2.0 specifications in Go. It generates server, client, and CLI code from a specification document, and can also produce a specification by scanning annotated Go source code. The project includes a static validation engine that checks documents against the schema and project-specific rules, and a specification transformation pipeline that resolves, flattens, and merges documents. The toolkit generates both client and server code from the same specification, ensuring consistency in request and response handling. It also produces a command

OpenAPI Generator CLI is a command-line utility designed to automate the creation of API artifacts from specification files. It functions as a tool for generating client libraries, server stubs, and documentation, enabling developers to produce consistent boilerplate code and reference materials across various programming languages. The project provides a wrapper that manages the lifecycle of a Java-based execution engine, which performs the actual code synthesis using logic-less templates. To ensure reproducible results and avoid dependency conflicts on the host system, the tool supports ver

Swagger Codegen is a template-driven engine and multi-language toolkit used to generate API client SDKs, server stubs, and human-readable documentation from OpenAPI specifications. It translates these specifications into functional libraries and boilerplate routing code across various target programming languages. The tool utilizes a pluggable generator module system and an integrated template engine, allowing for the customization of generated source code and the creation of new language-specific generators. It supports flexible specification sourcing via local files, remote HTTP endpoints,

Postman is an API platform that enables users to build, test, and interact with APIs by sending HTTP requests and viewing responses directly within the tool. It provides a graphical interface for designing and managing sequences of API interactions, allowing users to create and organize related API requests into named collections for reuse and sharing. The platform supports automating API workflows through test scripts and built-in sequences, and facilitates collaboration by enabling teams to share collections, specifications, and workflows. Users can document APIs by attaching descriptions a

This project is a comprehensive backend framework built on NestJS, designed to accelerate the development of multi-tenant software-as-a-service applications. It provides a production-ready foundation that integrates essential infrastructure, including user authentication, subscription billing, and team management, into a modular, decorator-based architecture. The framework distinguishes itself by offering a complete suite of SaaS-specific orchestration tools, such as a built-in billing engine for managing recurring revenue and a multi-tenant database partitioning system. It also includes a ro

Skeleton Application for Laminas API Tools