RDoc

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What RDoc is

RDoc is a free documentation tool for Ruby projects that generates HTML pages and command-line reference material. Use `rdoc` to build documentation and `ri` to display it. It can read Ruby, C, and RBS source, as well as RDoc markup, Markdown, RD, and TomDoc files. RBS declarations can document classes, modules, methods, attributes, and constants, and add comments or type signatures to documentation for corresponding Ruby source.

For local development, its preview server watches source files and refreshes the browser after changes. It relies on Ruby’s built-in TCPServer and needs no external gems. The `rdoc -C` command reports documentation coverage; `rdoc -C1` adds parameter names to the report. Documentation generation can also be run through a Rake task or the RDoc API. Aliki is the included theme; the classic Darkfish theme is deprecated and planned for removal in v9.0. The current gem requires Ruby 3.2.0 or newer. RDoc is free software, with no paid plans or stated usage limits, and is provided without express or implied warranties.

Who it suits

RDoc suits Ruby developers who want to generate project documentation from source and markup files, then browse it as HTML or command-line reference material. It also supports teams that want to automate generation through Rake or the API and review documentation coverage.

What it does well

Generates HTML and command-line documentation for Ruby projects.
Processes Ruby, C, RBS, and multiple markup formats.
Local preview refreshes when watched source files change.
Coverage reports can include parameter names.
Generation can run through Rake or the RDoc API.

What to know first

The preview server is for local use and has no HTTPS or HTTP/2.
The current gem requires Ruby 3.2.0 or newer.
Darkfish is deprecated and planned for removal in v9.0.

Limits

RDoc is free software, and no usage limits are stated. Its local preview server has no HTTPS or HTTP/2 and is intended for local development only.

Plans

Plan	Billed and limits	Price
RDoc	Free software; no paid plans or usage limits stated	Free

As ruby.github.io lists them, read 8 Oct 2026. The maker's own page has the final word.

Getting started

Visit https://ruby.github.io/rdoc/.
Use Ruby 3.2.0 or newer for the current gem.
Generate documentation with `rdoc`, or automate it through a Rake task or the RDoc API.
Use `ri` to display command-line reference material.
Run the local preview server to view updates as source files change.

Verdict

Choose RDoc if your Ruby project needs generated HTML and command-line documentation, with source coverage reporting and a local preview. Look elsewhere if you need a preview server with HTTPS or HTTP/2; RDoc’s server is intended only for local development.

Questions

How much does RDoc cost?

RDoc is free software, with no paid plans or stated usage limits.

Which inputs can RDoc process?

It can process Ruby, C, and RBS source, along with RDoc markup, Markdown, RD, and TomDoc files.

What output does RDoc generate?

It generates HTML documentation and command-line reference material displayed with `ri`.

Can I generate documentation automatically?

Yes. Documentation generation can be done through a Rake task or programmatically with the RDoc API.

Does RDoc include a live preview?

Yes. Its local server watches source files and refreshes the browser when they change. It has no HTTPS or HTTP/2.

What Ruby version is required?

The current gem requires Ruby 3.2.0 or newer.

Facts from RDoc's own pages

Automation: The site documents generating RDoc through a Rake task and through a Ruby programmatic API. · ruby.github.io, 8 Oct 2026
Coverage reporting: The `rdoc -C` command reports documentation coverage, and `rdoc -C1` includes parameter names. · ruby.github.io, 8 Oct 2026
Documentation coverage: RDoc can report project documentation coverage with `rdoc -C`, with an option to include parameter names in the report. · ruby.github.io, 8 Oct 2026
Input formats: RDoc processes Ruby, C, and RBS source files, along with markup files. · ruby.github.io, 8 Oct 2026
Integration: Documentation can be generated using a Rake task or programmatically through the RDoc API. · ruby.github.io, 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. · ruby.github.io, 8 Oct 2026
License: RDoc is free software and may be redistributed under the terms in its license file. · ruby.github.io, 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. · ruby.github.io, 8 Oct 2026
Live preview: RDoc includes a local preview server that watches source files and refreshes the browser when they change. · ruby.github.io, 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. · ruby.github.io, 8 Oct 2026
Preview server: RDoc includes a local preview server that watches source files and refreshes the browser when they change. · ruby.github.io, 8 Oct 2026
Preview server dependencies: The preview server uses Ruby’s built-in TCPServer and requires no external dependencies, WEBrick, or other gems. · ruby.github.io, 8 Oct 2026
Preview server security: The preview server has no HTTPS or HTTP/2 and is intended for local development preview only. · ruby.github.io, 8 Oct 2026
Purpose: RDoc produces HTML and command-line documentation for Ruby projects, with `rdoc` and `ri` tools to generate and display it. · ruby.github.io, 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. · ruby.github.io, 8 Oct 2026
Release: RubyGems lists RDoc version 8.1.0, released September 28, 2026. · rubygems.org, 8 Oct 2026
Ruby requirement: RubyGems lists Ruby version 3.2.0 or newer as required for the current gem. · rubygems.org, 8 Oct 2026
Server dependency: The preview server uses Ruby's built-in TCPServer and requires no external gems. · ruby.github.io, 8 Oct 2026
Server limitation: The preview server has no HTTPS or HTTP/2 and is intended for local development preview only. · ruby.github.io, 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. · ruby.github.io, 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. · ruby.github.io, 8 Oct 2026
Warranty: The software is provided as is without express or implied warranties. · ruby.github.io, 8 Oct 2026

Where RDoc stands on Freedom251

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