Rails AI Context

Your coding agent guesses your Rails app. Let it ask.

Website · Quick start · FAQ · What it does · A closer look · How it works · Tools reference · Contributing

Contents

• What it does
• Try it in your Rails app
• A closer look: the schema, the model, the inherited filters, the trace, the app that cannot boot, the six rules
• The tools
• How it works
• What it costs
• Questions you should ask first
• What it will not do
• Install options and configuration
• Troubleshooting
• Development
• Contributing and security
• Learn more

What it does

An assistant writing Rails code knows what an average Rails app looks like. Yours has its own columns, associations, filters and test setup, and the assistant starts every session with none of that. It writes a migration for a column that exists, calls user.posts when the association is user.articles, scaffolds FactoryBot into a fixture suite, and misses the before_action a parent controller adds. You catch it, fix it, re-prompt, and something next to it breaks.

rails-ai-context gives the assistant 35 tools that read the app itself, over MCP from the AI tool or from the command line. Every answer is read from the app and says how sure it is, and most end with a hint for the next call.

Each line comes from the sample app in this repository, a blog with Devise, an admin namespace, a JSON API, a Sidekiq job and a FactoryBot suite. The website records the whole answers every time it is built, by running the gem at that commit: crisnahine.github.io/rails-ai-context.

The install writes the files each AI tool reads, so the assistant knows the tools exist and how to ask: the MCP config, one root context file with six anti-hallucination rules, and rules that load when a model, a controller or a migration is open. The tools are read-only, the SQL tool runs inside a read-only transaction, and files that hold secrets are never served.

Try it in your Rails app

Open your AI tool at the root of your Rails app and paste this. It installs the gem, sets up the AI tool you are in, checks the result and tells you the one step left.

Install the rails-ai-context gem in this Rails app so you can read its schema, models, routes and code through its tools instead of guessing.

1. Run ruby -v and bundle exec rails -v. rails-ai-context needs Ruby 3.1+ and Rails 7.0+. If either is older, stop and tell me.
2. Pick TOOL, the key for the AI tool you are: claude (Claude Code), cursor (Cursor), copilot (GitHub Copilot in VS Code), opencode (OpenCode), codex (Codex CLI). If you are another AI tool, stop and tell me to use the "Another MCP client" prompt instead.
3. Run bundle add rails-ai-context --group development --version '>= 5.35.0'. If the Gemfile already lists it, run bundle update rails-ai-context --conservative instead. Then run bundle exec rails-ai-context version: it must print 5.35.0 or newer, the first version with the flags used below. If it is older, the Gemfile pins it: change its rails-ai-context line to gem "rails-ai-context", ">= 5.35.0", group: :development and run bundle update rails-ai-context --conservative. If Bundler refuses (a frozen or deployment bundle), run gem install rails-ai-context -v '>= 5.35.0' instead and use rails-ai-context init --tools TOOL --defaults in step 4.
4. Run bundle exec rails generate rails_ai_context:install --tools TOOL --defaults. If it fails because the app can't boot, run bundle exec rails-ai-context init --tools TOOL --defaults instead; that one reads the source files when the app won't start.
5. Run bundle exec rails-ai-context tool onboard (or rails-ai-context tool onboard if you used gem install) and check it describes this app.
6. Tell me which files changed, then the "Next step" lines the install printed for TOOL, word for word. I have to do that step before your rails-ai-context MCP tools appear.

<!-- END install-prompt -->

Rather type it yourself? In the Gemfile:

bundle add rails-ai-context --group development

bin/rails generate rails_ai_context:install --tools claude --defaults

Standalone, with no Gemfile change:

gem install rails-ai-context

rails-ai-context init --tools claude --defaults

As a Claude Code plugin, which adds the MCP server and gives each session the six rules, and writes no context files. It runs the installed gem, so install that first, and run it in the app's folder:

gem install rails-ai-context

claude plugin install rails-ai-context --marketpla