Rails::Schema

Interactive HTML visualization of your Rails database schema. Introspects your app's models, associations, and columns, then generates a single self-contained HTML file with an interactive entity-relationship diagram.

No external server, no CDN — just one command and a browser.

Live example — generated from Fizzy, a modern spin on kanban for tracking just about anything, created by 37signals.

Installation

Add to your Gemfile:

gem "rails-schema", group: :development

Then run:

bundle install

Usage

Rake task

rake rails_schema:generate

This generates docs/schema.html by default. Open it in your browser.

Programmatic

Rails::Schema.generate(output: "docs/schema.html")

Configuration

Create an initializer at config/initializers/rails_schema.rb:

Rails::Schema.configure do |config|
  config.output_path = "docs/schema.html"
  config.title = "My App Schema"
  config.theme = :auto          # :auto, :light, or :dark
  config.expand_columns = false # start with columns collapsed
  config.exclude_models = [
    "ActiveStorage::Blob",
    "ActiveStorage::Attachment",
    "ActionMailbox::*"           # wildcard prefix matching
  ]
end

How it works

The gem parses your db/schema.rb file to extract table and column information — no database connection required. It also introspects loaded ActiveRecord models for association metadata. This means the gem works even if you don't have a local database set up, as long as db/schema.rb is present (which is standard in Rails projects under version control).

Features

• No database required — reads directly from db/schema.rb
• Force-directed layout — models cluster naturally by association density
• Searchable sidebar — filter models by name or table
• Click-to-focus — click a model to highlight its neighborhood, fading unrelated models
• Detail panel — full column list and associations for the selected model
• Dark/light theme — toggle or auto-detect from system preference
• Zoom & pan — scroll wheel, pinch, or buttons
• Keyboard shortcuts — / search, Esc deselect, +/- zoom, F fit to screen
• Self-contained — single HTML file with all CSS, JS, and data inlined

License

The gem is available as open source under the terms of the MIT License.