Pretty much every day someone asks me if there's a tool for solving a specific API problem. While Runscope solves many API problems (particularly debugging, testing and monitoring) for app developers, there are many things we don't do. My goal with this post is to list out all the API tools that I know of and frequently recommend to people. Some even compete with us, but the more the merrier.

I've left out code libraries and frameworks since that would make the post too long.

Webhook Debugging

RequestBin - The original POST catcher, formerly postbin.org. Inspect HTTP requests. (Free)

- The original POST catcher, formerly postbin.org. Inspect HTTP requests. (Free) Webhook Inbox - Receives HTTP requests and captures the data for later inspection. (Free)

- Receives HTTP requests and captures the data for later inspection. (Free) RespondTo.it - Debug web hooks like a pro. Supports custom responses. (Free)

- Debug web hooks like a pro. Supports custom responses. (Free) InspectBin - Similar to RequestBin with live updates (Free)

- Similar to RequestBin with live updates (Free) Runscope Request Captures - HTTP request inspection with sharing, live updates, SSL, persistent URLs, search, comparisons and more. (Free + Paid)

Webhook Utilities

Hookify - Filter, manipulate, combine and forward webhook events. (Private Beta)

- Filter, manipulate, combine and forward webhook events. (Private Beta) Webhooks.io - Fast, reliable, scalable webhook delivery platform. (Private Beta)

- Fast, reliable, scalable webhook delivery platform. (Private Beta) Webscript - Webhook receiver and scripting engine using Lua. (Free + Paid)

- Webhook receiver and scripting engine using Lua. (Free + Paid) Torpio - JavaScript micro scripting platform for joining up & extending cloud apps. (Free + Paid)

Local Tunneling

API Monitoring

Runscope Radar - Global API monitoring and testing with flexible assertions, chained requests and OAuth support. Integrates with PagerDuty, New Relic, HipChat, Slack, Keen IO and more. (Free + Paid)

- Global API monitoring and testing with flexible assertions, chained requests and OAuth support. Integrates with PagerDuty, New Relic, HipChat, Slack, Keen IO and more. (Free + Paid) APImetrics - Real-time API tests & performance analysis. (Free + Paid)

Response Mocking

JsonStub - Fake the backend while you develop the front end. (Free, Beta)

- Fake the backend while you develop the front end. (Free, Beta) Mockable - Create REST and SOAP services which mimic your external providers. (Free, Preview)

- Create REST and SOAP services which mimic your external providers. (Free, Preview) mocky.io - Mock your HTTP responses to test your REST API. (Free)

- Mock your HTTP responses to test your REST API. (Free) httpbin.org - HTTP responses for common scenarios like status codes, delays, streaming, etc. (Free)

- HTTP responses for common scenarios like status codes, delays, streaming, etc. (Free) pathod - A pathological web daemon. (Free)

JSON Utilities

JSON formatter and validator - Paste in raw JSON, get a formatted, validated version back. (Free + Donations)

- Paste in raw JSON, get a formatted, validated version back. (Free + Donations) JSON format - Paste or load JSON from a URL to format it. (Free)

- Paste or load JSON from a URL to format it. (Free) JSON Schema Lint - JSON schema validator to assist you in the writing and testing of JSON Schemas that conform with the Draft 03 specification. (Free)

- JSON schema validator to assist you in the writing and testing of JSON Schemas that conform with the Draft 03 specification. (Free) JSON Generator - Generate sample JSON data with a comprehensive templating system. (Free)

- Generate sample JSON data with a comprehensive templating system. (Free) JSON editor online - Edit JSON via a GUI. (Free)

OAuth Utilities

foauth.org - Simplifies access to your data for services that use OAuth. (Free)

- Simplifies access to your data for services that use OAuth. (Free) OAuth.io - The fastest way to integrate OAuth (Free + Paid)

- The fastest way to integrate OAuth (Free + Paid) Runscope OAuth 2 Token Generator - Generate OAuth 2 access tokens without having to set up a server. (Free)

- Generate OAuth 2 access tokens without having to set up a server. (Free) Runscope OAuth 1.0a Token Generator - Generate OAuth 1.0a access tokens without having to set up a server. (Free)

API Directories

API Documentation

Apiary - Collaborative design, instant API mock, generated documentation, integrated code samples, debugging and automated testing. (Free + Paid)

- Collaborative design, instant API mock, generated documentation, integrated code samples, debugging and automated testing. (Free + Paid) API Blueprint - API documentation format used by Apiary and other tools. (Free)

- API documentation format used by Apiary and other tools. (Free) RAML - RESTful API Modeling Language. (Free)

- RESTful API Modeling Language. (Free) Swagger - Specification and complete framework implementation for describing, producing, consuming, and visualizing RESTful web services. (Free)

- Specification and complete framework implementation for describing, producing, consuming, and visualizing RESTful web services. (Free) I/O Docs - Fast, powerful API documentation & test calls. (Free)

- Fast, powerful API documentation & test calls. (Free) Embedcurl.com - Embeddable curl commands for your web site, blog or API documentation. (Free)

API Testing

Runscope Radar - HTTP/RESTful API testing in the cloud. Run your tests on every commit, build or deploy with email and webhook notifications for failures. (Free + Paid)

- HTTP/RESTful API testing in the cloud. Run your tests on every commit, build or deploy with email and webhook notifications for failures. (Free + Paid) SoapUI - SoapUI is a free and open source cross-platform Functional Testing solution. (Free + Paid)

- SoapUI is a free and open source cross-platform Functional Testing solution. (Free + Paid) StopLight - A powerful HTTP testing tool. (Free, Beta)

- A powerful HTTP testing tool. (Free, Beta) pathoc - A perverse HTTP client. (Free)

Cloud-based Debugging Proxies

Runscope Traffic Inspector - Log and inspect HTTP API calls from any language or framework to any API. Share, search, retry, compare requests and more. (Free + Paid)

- Log and inspect HTTP API calls from any language or framework to any API. Share, search, retry, compare requests and more. (Free + Paid) API Tools - Track, transform and analyze the traffic between your app and the APIs you use. (Free)

Desktop Debugging Proxies

Charles - Charles is an HTTP proxy / HTTP monitor / Reverse Proxy that enables a developer to view all of the HTTP and SSL / HTTPS traffic between their machine and the Internet. Supports OS X, Linux and Windows. (Paid)

- Charles is an HTTP proxy / HTTP monitor / Reverse Proxy that enables a developer to view all of the HTTP and SSL / HTTPS traffic between their machine and the Internet. Supports OS X, Linux and Windows. (Paid) Fiddler - The free web debugging proxy for any browser, system or platform. (Free)

- The free web debugging proxy for any browser, system or platform. (Free) mitmproxy - Intercept, modify, replay and save HTTP/S traffic. (Free)

- Intercept, modify, replay and save HTTP/S traffic. (Free) Burp Suite - Integrated platform for performing security testing of web applications. (Paid)

- Integrated platform for performing security testing of web applications. (Paid) HTTP Scoop - The HTTP sniffer for Mac OS X. (Paid)

API Gateway (Self-Hosted)

Tyk - An open source, lightweight, fast and scalable API Gateway. (Free + Paid)

- An open source, lightweight, fast and scalable API Gateway. (Free + Paid) ApiAxle - A proxy that sits on your network, in front of your API(s) and manages things that you shouldn't have to, like rate limiting, authentication and analytics. (Free)

- A proxy that sits on your network, in front of your API(s) and manages things that you shouldn't have to, like rate limiting, authentication and analytics. (Free) 3scale - "3scale provides a hybrid (API traffic management on-premise, API administration, traffic reports and developer portal cloud based) full featured API Management solution that is highly scalable, secure and flexible to match the most demanding requirements." (Free + Paid)

Load Testing

Loader.io - Stress test your web apps/APIs with thousands of concurrent connections. (Free + Paid)

- Stress test your web apps/APIs with thousands of concurrent connections. (Free + Paid) Blitz.io - Performance testing for websites, web apps and REST APIs. (Paid)

- Performance testing for websites, web apps and REST APIs. (Paid) BlazeMeter - JMeter load testing. Test the performance of any mobile app, website or API. (Free + Paid)

- JMeter load testing. Test the performance of any mobile app, website or API. (Free + Paid) LoadUI - API load testing solution. (Paid)

Command Line Tools

HTTPie - HTTPie is a command line HTTP client, a user-friendly cURL replacement. (Free)

- HTTPie is a command line HTTP client, a user-friendly cURL replacement. (Free) jq - Lightweight and flexible command-line JSON processor. (Free)

GUI HTTP Clients

Hurl.it - Make HTTP requests. (Free)

- Make HTTP requests. (Free) Postman for Chrome - There are many Chrome apps for making HTTP requests, this one is the best. (Free + Paid)

- There are many Chrome apps for making HTTP requests, this one is the best. (Free + Paid) Paw 2 - OS X HTTP client. (Paid)

- OS X HTTP client. (Paid) Echo - Another OS X HTTP client. (Paid)

Did I miss something?

I almost certainly did. Let me know in the comments!