Top Open Source API Development & Testing Tools in 2026
A curated collection of the 134 best free and open-source API Development & Testing tools in 2026. Compare features, GitHub stars, tech stacks, and self-hosted software.
Yaak
Local-first API client for HTTP, GraphQL, gRPC, and more
Stars19,117Last commit12d agoLicenseMIT
Usertour
Open-source user onboarding platform
Stars2,292Last commit10d agoLicenseOpen SourceUnKey
Unified API platform for deployment and observability
Stars5,423Last commit11d agoLicenseOpen Source
Stormkit
Self-hosted Vercel and Netlify alternative
Stars255Last commit10d agoLicenseOpen Source
Silex
Free open-source visual website builder
Stars2,937Last commit16d agoLicenseAGPL-3.0
Skyvern
AI-powered browser automation for any website
Stars22,857Last commit12d agoLicenseAGPL-3.0Reflet
Feedback platform for developer-led SaaS teams
Stars33Last commit14d agoLicenseOpen Source
Papermark
Open-source DocSend alternative with analytics
Stars8,977Last commit11d agoLicenseOpen SourceOpeninary
Open-source Cloudinary alternative for self-hosting
Stars384Last commit18d agoLicenseAGPL-3.0
OpenSign
Free open-source DocuSign alternative
Stars6,919Last commit16d agoLicenseOpen Source
Lua.sh
Open-source URL shortener for modern teams
Stars338Last commit5mo agoLicenseAGPL-3.0Ikiform
Open-source form builder with AI analytics
Stars356Last commit3mo agoLicenseMIT
Gravitee
AI Agent Management platform for enterprise scale
Stars445Last commit10d agoLicenseApache-2.0
Bifrost
Enterprise-grade AI gateway for LLM routing & governance
Stars7,598Last commit10d agoLicenseApache-2.0Lago
Open-source billing infrastructure for AI and tech businesses
Stars10,418Last commit11d agoLicenseAGPL-3.0
