Herb is an ecosystem of developer tooling built specifically around HTML+ERB (.html.erb) files. It is designed to simplify and enhance the experience of working with HTML+ERB templates through precise, accurate tooling.

At the core of Herb is the Herb Parser, a fast, portable, and HTML-aware ERB parser written in C. The parser generates a detailed, accurate syntax tree that serves as the foundation for reliable code analysis, transformations, and developer tooling.

The Herb ecosystem includes developer tools (CLI, language server, formatter, linter), language bindings (for Ruby, Node.js, and the Browser using WebAssembly), and utility libraries (language service, highlighter, minifier, printer). All these components leverage the Herb Parser's syntax tree to provide consistent, accurate, and helpful tooling experiences.

Herb provides a complete ecosystem of HTML+ERB tooling, designed to simplify and enhance your daily workflow. Built on the Herb Parser, it offers multiple tools that integrate seamlessly into editors, developer environments, and CI pipelines:

• Herb Language Server (available now): Rich integration for editors like VS Code, Zed, Neovim, and more. It provides diagnostics and real-time feedback to keep your templates error-free.

• Herb Formatter (experimental preview): Automatic, consistent formatting for HTML+ERB files, reducing manual styling and enforcing a standard across projects. Currently in experimental preview - use with caution on version-controlled files.

• Herb Linter (available now):
  Static analysis for your HTML+ERB templates to enforce best practices and quickly identify common mistakes with 17 configurable rules.

You can use Herb programmatically in Ruby, as well as in JavaScript via Node.js, WebAssembly, or directly in browsers.

For a complete overview of all available tools, libraries, and integrations, visit the Projects page on our documentation site.

HTML+ERB templates never really had good, accurate, and reliable tooling. While developer tooling for Ruby code improved significantly in the last few years (especially with the introduction of the new Prism parser), HTML+ERB files remained underserved, lacking fundamental support like syntax checking, auto-formatting, linting, and structural understanding.

At the same time, with the rise of tools like Hotwire, Stimulus, Turbo, HTMX, Unploy, and Alpine.js, advanced HTML templating became increasingly relevant (again). Developers expect modern, reliable, and precise tooling, especially given the robust ecosystem available to JavaScript frameworks and libraries.

Herb was built to close this tooling gap, providing proper tooling for HTML+ERB that matches what modern developers expect in the age of language servers, LLMs, and AI-driven workflows.

Install the Herb gem via RubyGems:

gem install herb

Basic usage to analyze all HTML+ERB files in your project:

herb analyze .

This will give you an overview of how the Herb Parser sees your project:

--- SUMMARY --------------------------------------------------------------------
Total files: 145
✅ Successful: 143 (98.6%)
❌ Failed: 0 (0.0%)
⚠️ Parse errors: 2 (1.4%)
⏱️ Timed out: 0 (0.0%)

Files with parse errors:
  - app/views/contributions/index.html.erb
  - index.html.erb

Results saved to 2025-06-29_12-16-23_erb_parsing_result_rubyevents.log

Herb also comes with other useful commands:

Herb 🌿 Powerful and seamless HTML-aware ERB parsing and tooling.

Usage:
  bundle exec herb [command] [options]

Commands:
  bundle exec herb lex [file]         Lex a file.
  bundle exec herb parse [file]       Parse a file.
  bundle exec herb analyze [path]     Analyze a project by passing a directory to the root of the project
  bundle exec herb ruby [file]        Extract Ruby from a file.
  bundle exec herb html [file]        Extract HTML from a file.
  bundle exec herb playground [file]  Open the content of the source file in the playground
  bundle exec herb version            Prints the versions of the Herb gem and the libherb library.

For detailed information, like how you can use Herb progamatiacally in Ruby and JavaScript, visit the documentation site.

Herb was first introduced at RubyKaigi 2025 in April 2025 with the talk Empowering Developers with HTML-Aware ERB Tooling.

Bug reports and pull requests are welcome on GitHub. Please see the CONTRIBUTING.md document for guidelines on how to set up Herb for local development and how to contribute to Herb.

While Herb brings a fresh approach to HTML+ERB tooling, it builds upon and learns from several existing tools and approaches in the ecosystem:

• Tree-sitter
• tree-sitter-embedded-template
• Prism Ruby Parser
• Ruby LSP
• better-html
• erb_lint
• erb-formatter
• erb-formatter-vscode
• deface
• html_press
• htmlbeautifier
• vscode-erb-beautify
• vscode-erb-linter

Herb differentiates itself by being HTML-aware from the ground up, providing a unified parsing approach that understands both HTML and ERB as first-class citizens, rather than treating one as embedded within the other.

This project is available as open source under the terms of the MIT License.