Free
Primer
Open SourceDesign Systems · Design & Prototyping
GitHub's design system with React components and tokens.
design-systemgithubreact
Browse the complete directory — use filters to narrow down.
Design Systems · Design & Prototyping
GitHub's design system with React components and tokens.
Cheatsheets & Learning · Git & Version Control
The official, free Pro Git book covering Git in depth.
Practice & Challenges · Documentation & Learning
Mathematical and computational programming problems.
Logs & Metrics · Monitoring & Observability
The standard open-source metrics collection and alerting toolkit.
Agent & LLM Frameworks · AI for Developers
The most comprehensive open guide to prompting techniques.
Other Formats · Data Formats
Official Protocol Buffers documentation from Google.
References · Documentation & Learning
The largest curated directory of free public APIs — 1,400+ entries across 40 categories with auth requirements noted.
Vector Databases · AI for Developers
Open-source vector database written in Rust, with cloud offering.
QR & Barcode · Encoding & Decoding
Free QR code generator with custom colors, shapes and logos.
Cheatsheets · Documentation & Learning
Clean, searchable cheat sheet collection for developers.
JSON · Data Formats
Generate types and serializers from JSON: TypeScript, Java, Kotlin, Go and more.
Models & LLM APIs · AI for Developers
Alibaba's open-weight model family with multilingual strengths.
Queues & Streaming · Database
Reliable, widely-deployed message broker with AMQP.
Favicons & Social Images · Image & Media
Generate all favicon formats with platform-by-platform previews.
Regex
Generate regular expressions from sample text matches.
Regex
Learn regular expressions step by step with interactive examples.
Regex
Visualize regular expressions as railroad diagrams.
Regex
Online regex tester with reference, cheatsheet and community patterns.
Comprehensive regex tutorial and reference for all flavors.
Smart Contracts · Web3 & Blockchain
Browser IDE for Solidity — write, compile, deploy and debug contracts with zero local setup.
Tunneling & Debugging · API Tools
Open-source HTTP interception: modify requests, mock, and debug in browser.
References · Documentation & Learning
Official repository of Internet RFC specifications.
Web Analytics · Monitoring & Observability
Google's validator for structured data — check JSON-LD eligibility for snippets, breadcrumbs and products.
Courses & Tutorials · Documentation & Learning
Community-driven developer roadmaps, guides and skill assessments.