Open-source alternatives to Yapi

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

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

NSwag is an OpenAPI toolchain for .NET that provides a suite of generators for converting OpenAPI specifications and JSON schemas into clients, server stubs, and structured documentation. It enables the creation of type-safe client libraries and data transfer objects, as well as the generation of OpenAPI specifications by analyzing .NET controllers. The project supports contract-first API development by generating server controller stubs from specifications and offers dedicated TypeScript API integration to ensure type safety in frontend applications. It also provides tools for hosting intera

openapi-ts is a tool and orchestrator used to convert OpenAPI specifications into type-safe TypeScript SDKs and HTTP client implementations. It automatically generates typed interfaces and request functions from API definitions to ensure consistency between the server and the client. The project employs a transport-agnostic client interface, decoupling high-level API calls from the underlying network library. It uses a plugin-based generation pipeline and a custom plugin architecture to allow for the customization of output types and validation schemas. The system provides capabilities for n

Thunder Client is a REST API client extension for VS Code that functions as an HTTP request manager, testing tool, and mocking workspace. It allows users to send requests, organize them into collections, and manage API configurations directly within the editor. The project distinguishes itself through a command-line interface for executing automated test suites in CI/CD pipelines and a Git-based synchronization system for sharing request collections and environment configurations across teams. It also incorporates artificial intelligence to automate the conversion of API scripts during migrat

Yaak is a cross-platform desktop client and command-line utility designed for developing, testing, and debugging API endpoints. It supports multi-protocol request execution for REST, GraphQL, and gRPC services, providing a unified environment for managing network interactions, authentication credentials, and automated testing workflows. The tool distinguishes itself through a local-first architecture that stores all workspace configurations and request definitions directly on the filesystem. This design enables native integration with version control systems like Git, allowing teams to track

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

Aglio is a command-line interface tool and static HTML renderer designed to convert API Blueprint specification files into readable, web-based documentation. It transforms structured API specifications into standalone HTML pages that can be hosted and distributed without a backend server. The project includes a theme engine that allows for the customization of visual styles through CSS variables and layout template overrides. Users can apply built-in themes or integrate external modules to change how the documentation is rendered. The tool supports modular document composition, enabling the

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

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

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

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

This project is a web-based documentation viewer and interactive console designed to render API specifications into browser-based interfaces. It provides a framework for exploring endpoints, managing authorization flows, and executing live test requests directly against defined services. By parsing specification files into structured data models, the tool generates dynamic interfaces that allow developers to interact with API definitions in real time. The console is built as a library of reusable web components, enabling developers to embed documentation viewers into existing web applications

Swagger Editor is a web-based authoring tool and development environment used to design, document, and validate API specifications. It specifically supports the OpenAPI Specification, providing a browser interface for writing API schemas and verifying their structure. The tool features real-time rendering that produces a visual preview of the API documentation as the specification is edited. It includes syntax highlighting based on standardized schemas to improve the readability of the API definitions. The editor supports importing specifications from files, external URLs, or example fixture

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

Anchor is a framework for building, testing, and deploying Solana smart contracts. It provides a Rust domain-specific language (DSL) that uses macro‑based instruction dispatch and derive‑macro account validation to automate ownership checks, discriminator enforcement, and serialization before instruction execution. The framework also includes a CLI toolchain for scaffolding, compiling, and managing contracts across workspaces, a test harness that simulates program execution with account manipulation and compute unit benchmarking, and an IDL generator that emits a standardized JSON interface fr

ServiceStack is a high-performance .NET web framework designed for building type-safe APIs using strongly-typed request and response objects. It functions as a message-based API engine that decouples business logic from the transport layer, allowing services to be exposed via multiple protocols including HTTP, gRPC, and various message queue providers. The framework is distinguished by its type-safe API generator, which produces native client SDKs and data transfer objects from service metadata across multiple languages. It also includes a distributed service gateway for microservices orchest

springdoc-openapi is a library and toolset that analyzes Spring applications at runtime to produce machine-readable OpenAPI specifications in JSON and YAML formats. It serves as an integrator that extracts API metadata from Java source code and annotations to automate documentation for Spring-based services. The project distinguishes itself through its ability to aggregate API specifications from multiple remote microservices into a single unified interface and provide multiple visualization options, including Swagger UI and Scalar. It also offers a dedicated plugin for exporting documentatio

Twirp is a Protocol Buffers RPC framework designed for implementing type-safe, distributed microservices communication over HTTP. It functions as a microservices communication framework and API code generator that produces strongly typed client stubs and server interfaces from schema definitions to eliminate manual network boilerplate. The framework ensures compatibility with existing web infrastructure by executing remote procedure calls over standard HTTP transport. It uses schema-driven contracts as a single source of truth to enable cross-language interoperability and decouple business lo

vibe-vibe is an LLM agent engineering framework and toolchain optimizer designed for orchestrating multi-agent systems. It serves as a comprehensive guide and methodology for transforming conceptual ideas into deployed applications through agentic software engineering. The project focuses on the orchestration of specialized AI agent roles with defined collaboration boundaries and iterative feedback loops. It provides frameworks for toolchain optimization, including the selection and evaluation of protocols that extend model capabilities and the design of standardized tool interfaces. The sys

This project is a command-line tool that automates the creation of type-safe TypeScript HTTP clients directly from OpenAPI specifications. By transforming service definitions into structured source code, it ensures end-to-end type synchronization and enforces runtime data integrity across network boundaries. The generator distinguishes itself by mapping OpenAPI data structures into Zod validation schemas, allowing for consistent schema-driven type mapping and response validation. It supports deduplicated source synthesis to minimize redundancy in the generated output and provides template cus

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

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

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

This project is an end-to-end encrypted communication client designed for secure messaging and identity management using public-key cryptography. It provides a cryptographic identity manager to verify authenticity across platforms and integrates a local messaging daemon to synchronize encrypted data and handle network communication. The system features a remote encrypted file system that mounts encrypted storage as local directories for direct file interaction. It also includes automated identity provisioning for registering and authenticating new devices and automation bots using cryptograph