Tools

Write, lint and publish API descriptions such as OpenAPI and AsyncAPI.

• AsyncAPI ToolingThe AsyncAPI Initiative's open-source tools for event-driven API documents: the CLI, Studio, Generator, Modelina and parsers.Open source
• Bump.shA hosted documentation platform for OpenAPI and AsyncAPI that diffs every release, flags breaking changes and publishes an automatic changelog.Paid
• gRPC & Protobuf ToolingThe compilers, code generators, linters and debugging tools around gRPC and Protocol Buffers: protoc and its plugins, Buf, grpcurl, server reflection and health checking.Open source
• legibleAn OpenAPI linter that scores how well a specification survives conversion into agent tool definitions, and explains every finding.Open source
• MintlifyA hosted docs-as-code platform: MDX pages in a Git repository, configured by docs.json, with API reference pages generated from OpenAPI and AsyncAPI.Freemium
• ReadMeA hosted API documentation platform that turns OpenAPI into an interactive reference, with guides, Git sync, the rdme CLI and API usage metrics.Freemium
• Redoc (Redocly)Generates clean, responsive, and highly readable API reference documentation from OpenAPI specifications.Freemium
• ScalarAn MIT-licensed interactive API reference and API client for OpenAPI documents, with a hosted platform for docs, SDKs and MCP servers.Freemium
• Spectral (Stoplight)A flexible, JSON/YAML linter for checking API designs against custom style rules and OpenAPI standards.Open source
• Swagger (SmartBear)SmartBear's Swagger tooling for OpenAPI: the open-source Swagger Editor, Swagger UI and Swagger Codegen, and a commercial design, documentation and testing platform.Freemium
• TypeSpecMicrosoft's MIT-licensed language for describing APIs, compiled to OpenAPI 3, JSON Schema and Protocol Buffers through emitters.Open source
• vacuumA fast, MIT-licensed OpenAPI, AsyncAPI, Arazzo and JSON Schema linter written in Go, compatible with Spectral-style rulesets.Open source

Generate typed client libraries from an API description.

• FernA hosted platform, owned by Postman since January 2026, that generates SDKs in nine languages and documentation sites from OpenAPI, AsyncAPI and gRPC definitions.Freemium
• KiotaMicrosoft's MIT-licensed command-line generator of strongly typed API clients from OpenAPI, built on shared per-language core libraries, with path filtering to generate only the operations you call.Open source
• OpenAPI GeneratorA community-maintained, Apache-2.0 generator of client SDKs, server stubs and documentation from OpenAPI 2.0 and 3.x, forked from Swagger Codegen in 2018.Open source
• SpeakeasyAn OpenAPI SDK generator for seven languages, plus CLI, MCP server and Terraform provider generation, open-sourced under AGPL-3.0 with commercial licensing.Freemium
• StainlessA hosted generator of SDKs, Terraform providers, MCP servers and docs from OpenAPI. Closed to new signups and projects since May 2026, when Stainless joined Anthropic and began winding down its hosted products.Freemium

Mock servers, contract tests and load tests.

• ArtilleryA load testing toolkit with YAML scenarios and JavaScript hooks, HTTP, WebSocket, Socket.IO and gRPC support, Playwright browser tests, and distributed runs on AWS Lambda or Fargate. Core is MPL-2.0.Open source
• GatlingA load testing tool with simulations written as code in Java, Kotlin, Scala, JavaScript or TypeScript. The Community Edition is Apache-2.0; Enterprise Edition adds managed load generation and team features.Open source
• Grafana k6A developer-centric load and performance testing tool scripted in JavaScript and executed in Go.Open source
• HurlA command-line tool from Orange that runs and tests HTTP requests written in a plain-text format, with captures, assertions and CI reports.Open source
• KarateAn open-source test framework from Karate Labs that combines API tests, mocks, performance tests and UI automation in a single readable DSL on the JVM.Freemium
• MicrocksA CNCF open-source platform that turns OpenAPI, AsyncAPI, gRPC, GraphQL, Postman and SoapUI artifacts into live mocks and contract tests.Open source
• MockoonAn easy-to-use local desktop mock server generator featuring a graphical interface.Freemium
• NewmanA command-line collection runner for Postman, allowing tests to be integrated directly into CI/CD pipelines.Open source
• OpticAn OpenAPI diffing, linting and breaking-change tool whose repository was archived in January 2026 after Optic Labs joined Atlassian.Open source
• PactA consumer-driven contract testing framework that lets services verify their integrations without spinning up full end-to-end environments.Open source
• PostmanA comprehensive API platform for building, testing, organizing, and collaborating on HTTP requests.Freemium
• Prism (Stoplight)An open-source mock server that parses OpenAPI specifications and runs mock API endpoints.Open source
• REST AssuredAn open-source Java DSL for testing HTTP APIs with given/when/then syntax, JSON and XML path assertions, and JSON Schema validation.Open source
• SchemathesisA property-based API testing tool that generates thousands of requests from an OpenAPI or GraphQL schema and checks every response against it.Open source
• SoapUIA functional testing application for SOAP and REST APIs, designed for testing complex enterprise integrations.Freemium
• WireMockA simulator for HTTP-based APIs, enabling developers to mock downstream dependencies in integration tests.Open source

Audit API contracts and attack running APIs to find vulnerabilities before someone else does.

• 42CrunchA commercial API security platform built on the OpenAPI contract: static audit of the definition, dynamic scanning of the running API against it, and a contract-derived runtime firewall.Paid
• Burp SuitePortSwigger's web security testing toolkit: a free Community Edition for manual testing, Professional for penetration testers, and Burp Suite DAST for scanning at scale, with API scans from OpenAPI definitions.Freemium
• StackHawkA commercial DAST platform whose HawkScan scanner runs locally or in CI against REST, GraphQL, gRPC and SOAP APIs, configured with a stackhawk.yml file in the repository.Paid
• ZAP (Zed Attack Proxy)A free, Apache-2.0 dynamic application security scanner, formerly OWASP ZAP and now published as ZAP by Checkmarx, with a packaged scan for OpenAPI, SOAP and GraphQL APIs.Open source

Send requests, inspect traffic and see exactly what came back.

• BrunoA fast, git-friendly open-source API client that stores collections directly as folder structures.Freemium
• Charles ProxyAn HTTP proxy and monitor that enables developers to view and inspect all HTTP traffic between their machine and the internet.Paid
• curlThe ubiquitous command-line tool and library for transferring data with URLs using HTTP, HTTPS, and dozens of protocols.Open source
• Fiddler (Progress)A classic debugging proxy for routing, decrypting, and rewriting HTTP traffic.Paid
• HoppscotchAn open-source, browser-based API client for building and testing HTTP, GraphQL, WebSocket, and other requests, with a self-hostable option.Freemium
• HTTPieA command-line HTTP client built for developers, offering clean syntax, syntax highlighting, and auto-formatted JSON.Open source
• InsomniaA streamlined, desktop-based HTTP, REST, and GraphQL client built for local debugging and testing.Freemium
• mitmproxyAn interactive, SSL-capable intercepting HTTP proxy CLI and web tool built for developers.Open source
• ProxymanA native debugging proxy for macOS, Windows and Linux that captures and decrypts HTTPS traffic from desktop apps, browsers, iOS and Android.Freemium
• Thunder ClientA lightweight REST API client built into VS Code, with scriptless GUI tests and collections that can be saved to the project's Git repository.Freemium

Sit in front of an API to route, authenticate and rate-limit its traffic.

• Apigee (Google Cloud)An enterprise-grade API gateway and management platform providing security, analytics, and developer portal tools.Paid
• AWS API GatewayA fully managed service enabling developers to publish, maintain, and secure APIs at any scale in AWS.Paid
• Azure API ManagementMicrosoft's managed API gateway, management plane and developer portal, with a self-hosted gateway for running the data plane outside Azure.Paid
• Envoy ProxyA CNCF-graduated, open-source L7 edge and service proxy with dynamic xDS configuration, the data plane underneath many gateways and service meshes.Open source
• GraviteeAn API management platform with an Apache 2.0 open-source gateway, plus enterprise editions covering event streams, Kafka and AI agent traffic.Freemium
• Kong GatewayA cloud-native, high-performance API gateway built on Nginx, serving as a centralized proxy for routing and security.Freemium
• KrakenDAn ultra-performant, stateless API gateway built in Go, designed to handle large-scale routing without database dependencies.Freemium
• NGINXThe BSD-licensed web server, reverse proxy and load balancer that sits in front of a large share of HTTP APIs, with F5 NGINX Plus as its commercial edition.Freemium
• TraefikAn MIT-licensed cloud-native reverse proxy that configures routes from Kubernetes, Docker and other providers, with Traefik Hub adding commercial API gateway and API management layers.Freemium
• TykAn open-source, enterprise-grade API gateway and management platform built in Go.Freemium
• ZuploA serverless API gateway built for developers, offering git-ops workflows, rate limiting, and instant documentation.Freemium

Send, receive, retry and inspect webhooks without building the delivery system yourself.

• HookdeckWebhook infrastructure in both directions: Event Gateway queues, filters and retries incoming webhooks, and Outpost, open source under Apache-2.0, delivers outbound webhooks and events to customers.Freemium
• SvixWebhook sending as a service: one API call per event, with retries, signing, an embeddable consumer portal and receiving through Svix Ingest. The server is MIT-licensed and can be self-hosted.Freemium

Trace, log and measure an API in production.

• Datadog APMAn observability platform providing deep infrastructure monitoring, application performance monitoring (APM), and API log tracking.Paid
• Dynatrace APMEnterprise APM providing automatic service discovery, full-stack tracing, and AI-driven diagnostic alerts.Paid
• HoneycombAn OpenTelemetry-native observability platform built on high-cardinality events, for querying production behavior without pre-aggregation.Freemium
• JaegerA CNCF-graduated, open-source distributed tracing backend whose v2 is built on the OpenTelemetry Collector.Open source
• MoesifA user-centric API analytics and monetization platform designed for debugging, monitoring, and billing.Freemium
• New RelicA comprehensive APM and cloud monitoring tool providing real-time telemetry, transaction tracing, and alert configurations.Freemium
• Prometheus & GrafanaThe standard open-source time-series DB and dashboarding stack for API infrastructure metrics.Open source
• SentryA source-available error tracking and performance monitoring platform that groups exceptions and traces so developers can debug failures in production.Freemium
• TreblleAn API observability and governance platform that captures live request and response data through SDKs or gateway integrations, then scores, documents and audits your APIs.Paid