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.

Add to your Gemfile:

gem "rails-schema", group: :development

Then run:

bundle install

rake rails_schema:generate

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

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

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.schema_format = :auto  # :auto, :ruby, :sql, or :mongoid
  config.exclude_models = [
    "ActiveStorage::Blob",
    "ActiveStorage::Attachment",
    "ActionMailbox::*"           # wildcard prefix matching
  ]
end

Rails projects can use either db/schema.rb (Ruby DSL) or db/structure.sql (raw SQL dump) to represent the database schema. Set config.active_record.schema_format = :sql in your Rails app to use structure.sql.

If your app uses Mongoid instead of ActiveRecord, rails-schema can introspect your Mongoid models directly — no schema file needed.

Rails::Schema.configure do |config|
  config.schema_format = :mongoid
end

When set to :auto, Mongoid mode activates automatically if Mongoid::Document is defined.

The Mongoid pipeline reads fields, types, defaults, and presence validations from your models, and discovers all association types including embeds_many, embeds_one, embedded_in, and has_and_belongs_to_many.

The gem parses your db/schema.rb or db/structure.sql 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 a schema file is present (which is standard in Rails projects under version control).

For Mongoid apps, the gem introspects model classes at runtime to read field definitions, associations, and validations — no schema file or database connection required.

• No database required — reads from db/schema.rb, db/structure.sql, or Mongoid model introspection
• Force-directed layout — models cluster naturally by association density; self-referential-only models are placed in a left column, true orphans in rows above
• 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

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