RDoc
RDoc is free software for generating and viewing documentation for Ruby projects.
What RDoc is
RDoc is free software for generating and viewing documentation for Ruby projects. Its `rdoc` command produces HTML and RI reference output, while `ri` displays command-line documentation. It processes Ruby, C, and RBS source files, plus RDoc markup, Markdown, RD, and TomDoc documents. RBS declarations can document classes, modules, methods, attributes, and constants, and add comments or type signatures to matching Ruby source documentation. A local preview server watches source files and refreshes the browser after changes. The server uses Ruby’s built-in TCPServer and needs no external gems, but it is intended only for local development because it has no HTTPS or HTTP/2. RDoc can report documentation coverage with `rdoc -C`; `rdoc -C1` includes parameter names. Projects can automate generation through Rake or the RDoc API. The Aliki theme is included, while Darkfish is deprecated. The current gem requires Ruby 3.2.0 or newer.
Good
- Free software with no paid plans stated
- Generates HTML and RI documentation
- Processes Ruby, C, RBS, and markup
- Local preview server refreshes on changes
- Coverage reports include optional parameter names
Watch out
- Preview server has no HTTPS or HTTP/2
- Darkfish theme is deprecated
- Current gem requires Ruby 3.2.0 or newer
- Preview can temporarily lose reopened classes
Who it suits
RDoc suits Ruby project maintainers who need generated API references, command-line documentation, and local previews on Linux or self-hosted systems. It also fits teams documenting Ruby, C, or RBS sources in automation workflows.
Verdict
RDoc combines source processing, API output, coverage reporting, and a dependency-free local preview server. Its Linux and self-hosted focus, plus the Ruby version requirement and preview limitations, are important considerations.
Plans and prices
From RDoc's own pricing page, checked 8 Oct 2026.
| Plan | Price | What it gives you |
|---|---|---|
| RDoc | Free | Free software; no paid plans or usage limits stated |
The facts
Each one read from RDoc's own pages, with the date it was checked.
What it does
- Automation
- The site documents generating RDoc through a Rake task and through a Ruby programmatic API.checked 8 Oct 2026
- Coverage reporting
- The `rdoc -C` command reports documentation coverage, and `rdoc -C1` includes parameter names.checked 8 Oct 2026
- Documentation coverage
- RDoc can report project documentation coverage with `rdoc -C`, with an option to include parameter names in the report.checked 8 Oct 2026
- Input formats
- RDoc processes Ruby, C, and RBS source files, along with markup files.checked 8 Oct 2026
- Integration
- Documentation can be generated using a Rake task or programmatically through the RDoc API.checked 8 Oct 2026
- Known limitation
- Deleting a file that contains part of a class reopened across multiple files can temporarily remove the entire class from the preview store until another file is saved and reparsed.checked 8 Oct 2026
- License
- RDoc is free software and may be redistributed under the terms in its license file.checked 8 Oct 2026
- License and warranty
- RDoc describes itself as free software and states that it is provided as is without express or implied warranties.checked 8 Oct 2026
- Live preview
- RDoc includes a local preview server that watches source files and refreshes the browser when they change.checked 8 Oct 2026
- Markup
- RDoc supports RDoc markup, Markdown, RD, and TomDoc; the site recommends Markdown for standalone documentation and discourages new use of RD and TomDoc.checked 8 Oct 2026
- Preview server
- RDoc includes a local preview server that watches source files and refreshes the browser when they change.checked 8 Oct 2026
- Preview server dependencies
- The preview server uses Ruby’s built-in TCPServer and requires no external dependencies, WEBrick, or other gems.checked 8 Oct 2026
- Preview server security
- The preview server has no HTTPS or HTTP/2 and is intended for local development preview only.checked 8 Oct 2026
- Purpose
- RDoc produces HTML and command-line documentation for Ruby projects, with `rdoc` and `ri` tools to generate and display it.checked 8 Oct 2026
- RBS support
- RBS declarations can document classes, modules, methods, attributes, and constants, and can extend matching Ruby source documentation with comments and type signatures.checked 8 Oct 2026
- Release
- RubyGems lists RDoc version 8.1.0, released September 28, 2026.checked 8 Oct 2026
- Ruby requirement
- RubyGems lists Ruby version 3.2.0 or newer as required for the current gem.checked 8 Oct 2026
- Server dependency
- The preview server uses Ruby's built-in TCPServer and requires no external gems.checked 8 Oct 2026
- Server limitation
- The preview server has no HTTPS or HTTP/2 and is intended for local development preview only.checked 8 Oct 2026
- Support
- The project directs users to its contributing guide for filing bug reports and says problems producing desired output may be documentation bugs.checked 8 Oct 2026
- Themes
- RDoc includes the Aliki theme by default, while its classic Darkfish theme is deprecated and the site says it will be removed in v9.0.checked 8 Oct 2026
- Warranty
- The software is provided as is without express or implied warranties.checked 8 Oct 2026
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