MCP Tools Guide

MCP Tools Guide for Rails Development

Three MCP servers are available for Rails development. Use them to analyze codebases faster and more accurately than reading files manually.

Rails MCP Server

The primary tool for Rails codebase analysis.

Tool Discovery

mcp__rails__search_tools

Returns available analyzers organized by category:

• models — Model analysis, associations, validations
• database — Schema, migrations, indexes
• routing — Route analysis and listing
• controllers — Controller structure, actions, filters
• files — File listing and reading
• project — Project-wide analysis
• guides — Rails guides and documentation

Execute Analyzers

mcp__rails__execute_tool(tool_name: "tool_name", params: {...})

Ruby Execution

mcp__rails__execute_ruby(code: "...")

Read-only Ruby execution for custom analysis. Common queries:

# Model introspection
User.reflect_on_all_associations.map { |a| [a.macro, a.name] }
User.validators.map { |v| [v.class.name, v.attributes] }

# Database introspection
ActiveRecord::Base.connection.indexes(:users).map(&:columns)
ActiveRecord::Base.connection.columns(:users).map { |c| [c.name, c.type] }

# Migration status
ActiveRecord::Base.connection.execute(
  "SELECT * FROM schema_migrations ORDER BY version DESC LIMIT 10"
)

# Route inspection
Rails.application.routes.routes.map { |r|
  [r.verb, r.path.spec.to_s, r.defaults[:controller], r.defaults[:action]].join(' ')
}

# File discovery
Dir.glob('app/services/**/*.rb')
Dir.glob('app/javascript/controllers/**/*.js')
Dir.glob('app/views/**/*.turbo_stream.erb')
Dir.glob('app/channels/**/*.rb')
Dir.glob('app/components/**/*.rb')
Dir.glob('spec/**/*_spec.rb')
Dir.glob('spec/factories/**/*.rb')
Dir.glob('spec/support/**/*.rb')

Context7 MCP Server

Retrieves up-to-date documentation and code examples for any library.

Workflow

1. Resolve library ID first:

   mcp__plugin_context7_context7__resolve-library-id(
     libraryName: "rails",
     query: "your question"
   )
   

2. Query documentation:

   mcp__plugin_context7_context7__query-docs(
     libraryId: "/rails/rails",
     query: "your question"
   )
   

When to Use

• Verifying current Rails API behavior or method signatures
• Looking up gem documentation (Devise, Pundit, Sidekiq, etc.)
• Checking for deprecations in newer Rails versions
• Finding code examples for specific patterns
• Confirming configuration options and defaults

Common Library IDs

For other gems, always call resolve-library-id first.

Ruby LSP

Language-aware intelligence for Ruby code. Tools use the mcp__ruby-lsp__ prefix.

Key Tools

mcp__ruby-lsp__definition(uri: "file:///path/to/file.rb", line: 10, character: 5)

Jump to the definition of a method, class, or module at a given position.

mcp__ruby-lsp__references(uri: "file:///path/to/file.rb", line: 10, character: 5)

Find all usages of a symbol across the codebase.

mcp__ruby-lsp__symbol(query: "UserPolicy")

Search for classes, modules, and methods by name across the workspace.

Other Capabilities

• Type checking — Infer and validate types at a given position
• Intelligent completions — Context-aware code suggestions
• Diagnostics — Identify issues in Ruby code

When to Use

• When Rails MCP tools don't provide enough detail about specific method implementations
• When tracing method calls across the codebase
• When investigating inheritance hierarchies or module mixins
• When locating all callers of a method before refactoring

Quick Reference

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