lychee is a high-performance link checker built in Rust that validates hyperlinks and email addresses across multiple document formats. It processes HTML, Markdown, reStructuredText, and plain text files with exceptional speed using asynchronous, stream-based processing.

Key capabilities include:

Multi-format support: Check links in Markdown, HTML, reStructuredText, and text files, plus live websites
Advanced configuration: Custom headers, user agents, cookies, redirect handling, and basic authentication
Flexible filtering: Pattern-based inclusion/exclusion, status code filtering, and quiet mode for cleaner output
Integration-ready: JSON output format, GitHub token support, and pre-built binaries for seamless CI/CD pipeline integration
Dual deployment: Use as a standalone command-line tool or embed as a Rust library in your projects

lychee excels at maintaining documentation integrity by catching broken links in READMEs, websites, and repositories. Its portable single binary and async architecture make it ideal for both local development workflows and automated GitHub Actions pipelines. The tool's configurability handles diverse link-checking scenarios, from simple validation to complex authentication requirements.