Rails AI Context MCP Server

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rails-ai-context

Your AI is guessing your Rails app. Every guess costs you time.

<a href="https://claude.ai/claude-code"><img src="https://img.shields.io/badge/Claude_Code-ee8b4a?style=for-the-badge&logo=anthropic&logoColor=white" alt="Claude Code"></a> <a href="https://cursor.com"><img src="https://img.shields.io/badge/Cursor-000000?style=for-the-badge&logo=cursor&logoColor=white" alt="Cursor"></a> <a href="https://github.com/features/copilot"><img src="https://img.shields.io/badge/GitHub_Copilot-000000?style=for-the-badge&logo=githubcopilot&logoColor=white" alt="GitHub Copilot"></a> <a href="https://opencode.ai"><img src="https://img.shields.io/badge/OpenCode-4285F4?style=for-the-badge&logoColor=white" alt="OpenCode"></a> <a href="https://codex.openai.com"><img src="https://img.shields.io/badge/Codex_CLI-412991?style=for-the-badge&logo=openai&logoColor=white" alt="Codex CLI"></a> <a href="docs/CLI.md"><img src="https://img.shields.io/badge/Any_Terminal-4EAA25?style=for-the-badge&logo=gnubash&logoColor=white" alt="Any Terminal"></a>

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The problem

You've seen it. Your AI:

• Writes a migration for a column that already exists - didn't check the schema
• Creates a method that duplicates one in a concern - didn't know it was there
• Uses the wrong association name - user.posts when it's user.articles
• Generates tests that don't match your patterns - factories when you use fixtures, or the reverse
• Adds a gem you already have - or calls an API from one you don't
• Misses before_action filters from parent controllers - then wonders why auth fails
• Invents a method that isn't in your codebase - then you spend 10 minutes finding out

You catch it. You fix it. You re-prompt. It breaks something else.

The real cost of AI coding isn't the tokens - it's the correction loop. Every guess is a round-trip: you catch it, you fix it, you re-prompt, and something adjacent breaks. This gem kills the guessing at its source.

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Two commands. Problem gone.

gem "rails-ai-context", group: :development
rails generate rails_ai_context:install

Or standalone - no Gemfile needed

gem install rails-ai-context
cd your-rails-app
rails-ai-context init     # interactive setup
rails-ai-context serve    # start MCP server

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Now your AI doesn't guess - it asks your app directly. 38 tools and 5 resource templates that query your schema, models, routes, controllers, views, and conventions on demand. Model introspection uses Prism AST parsing - every result carries a [VERIFIED] or [INFERRED] confidence tag so AI knows what's ground truth and what needs runtime checking.

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See the difference

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One call returns: definition + source code + every caller grouped by type + tests. Replaces 4-5 sequential file reads.

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What stops being wrong

Real scenarios where AI goes sideways - and what it does instead with ground truth:

You ask AI to...	Without - AI guesses	With - AI verifies first
Add a subscription_tier column to users	Writes the migration, duplicates an existing column	Reads live schema, spots subscription_status already exists, asks before migrating
Call user.posts in a controller	Uses the guess; runtime NoMethodError	Resolves the actual association (user.articles) from the model
Write tests for a new model	Scaffolds with FactoryBot	Detects your fixture-based suite and matches it
Fix a failing create action	Misses inherited before_action :authenticate_user!	Returns parent-controller filters inline with the action source
Build a dashboard page	Invents Tailwind classes from memory	Returns your actual button/card/alert patterns, copy-paste ready
Trace where publishable? is used	Reads 6 files sequentially, still misses callers	Single call: definition + source + every caller + tests

<details> <summary><strong>Verify it on your own app</strong></summary> <br>

Run these before and after installing to see what changes in your codebase:

# Schema: does AI know what columns exist?
rails 'ai:tool[schema]' table=users

# Trace: find every caller of a method across the codebase
rails 'ai:tool[search_code]' pattern=your_method match_type=trace

# Model: associations, scopes, callbacks, concerns - all resolved
rails 'ai:tool[model_details]' model=User

# Controllers: action source + inherited filters + strong params in one shot
rails 'ai:tool[controllers]' controller=UsersController action=create

Compare what AI outputs with and without these tools wired in. The difference is measured in corrections avoided, not bytes saved.

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Three ways to use it

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MCP Server (stdio)

AI calls tools directly via the protocol. Each AI tool gets its own config file - auto-detected on project open.

rails ai:serve

→ rails_search_code(pattern: "publishable?", match_type: "trace")
→ rails_get_schema(table: "users")
→ rails_analyze_feature(feature: "billing")

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MCP Server (HTTP)

Mount inside your Rails app - inherits routing, auth, and middleware.

# config/routes.rb
mount RailsAiContext::Engine, at: "/mcp"

Native Rails controller transport. No separate process needed.

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CLI

Same 38 tools, no server needed. Works in any terminal, any AI tool.

rails 'ai:tool[search_code]' pattern="publishable?" match_type=trace
rails 'ai:tool[schema]' table=users
rails 'ai:tool[analyze_feature]' feature=billing

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Full Guide → - every command, every parameter, every configuration option.

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Real-world examples

<details> <summary><strong>"Add a subscription field to users"</strong></summary> <br>

rails 'ai:tool[schema]' table=users

## Table: users
| Column              | Type    | Null | Default |
|---------------------|---------|------|---------|
| email               | string  | NO   | [unique] |
| subscription_status | string  | yes  | "free"   |
| created_at          | datetime| NO   |          |

AI sees subscription_status already exists. Checks the model, then generates a correct migration - first attempt.

</details> <details> <summary><strong>"Fix the broken post creation flow"</strong></summary> <br>

rails 'ai:tool[controllers]' controller=PostsController action=create

# PostsController#create

Filters: before_action :authenticate_user!, before_action :set_post (only: show, edit)
Strong params: post_params → title, body, published_at
Renders: redirect_to @post | render :new

AI sees the inherited authenticate_user! filter, the actual strong params, and the render paths. No guessing.

</details> <details> <summary><strong>"Build a new dashboard view"</strong></summary> <br>

# Check existing view patterns
rails 'ai:tool[view]' controller=dashboard
# → templates with ivars, Turbo frames, Stimulus controllers, partial locals

# See existing components + usage examples
rails 'ai:tool[component_catalog]' detail=standard
# → ViewComponent/Phlex props, slots, previews, sidecar assets

# Get Stimulus data-attributes
rails 'ai:tool[stimulus]' controller=chart
# → correct HTML with dashes (not underscores) + reverse view lookup

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38 Tools

Every tool is read-only and returns data verified against your actual app - not guesses, not training data.

<details open> <summary><strong>Search & Trace</strong></summary>

Tool	What it does
search_code	Trace: definition + source + callers + tests. Also: definition, call, class filters
get_edit_context	Method-aware code extraction with class context

</details> <details open> <summary><strong>Understand</strong></summary>

Tool	What it does
analyze_feature	Full-stack: models + controllers + routes + services + jobs + views + tests
get_context	Composite: schema + model + controller + routes + views in one call
onboard	Narrative app walkthrough (quick/standard/full)

</details> <details open> <summary><strong>Schema & Models</strong></summary>

Tool	What it does
get_schema	Columns with indexed/unique/encrypted/default hints
get_model_details	AST-parsed associations, validations, scopes, enums, macros - each result tagged [VERIFIED] or [INFERRED]
get_callbacks	Callbacks in Rails execution order with source
get_concern	Concern methods + source + which models include it

</details> <details open> <summary><strong>Controllers & Routes</strong></summary>

Tool	What it does
get_controllers	Actions + inherited filters + render map + strong params
get_routes	Code-ready helpers (post_path(@record)) + required params

</details> <details open> <summary><strong>Views & Frontend</strong></summary>

Tool	What it does
get_view	Templates with ivars, Turbo wiring, Stimulus refs, partial locals
get_stimulus	HTML data-attributes (dashes!) + targets + values + actions
get_partial_interface	What locals to pass + what methods are called on them
get_turbo_map	Broadcast → subscription wiring + mismatch warnings
get_frontend_stack	React/Vue/Svelte/Angular, Hotwire, TypeScript, package manager

</details> <details open> <summary><strong>Testing & Quality</strong></summary>

Tool	What it does
get_test_info	Fixtures + relationships + test template matching your patterns
generate_test	Test scaffolding matching your project's patterns
validate	Syntax + semantic + Brakeman security in one call
security_scan	Brakeman static analysis - SQL injection, XSS, mass assignment
performance_check	N+1 risks, missing indexes, counter_cache, eager load candidates

</details> <details open> <summary><strong>App Config & Services</strong></summary>

Tool	What it does
get_conventions	Auth checks, flash messages, create action template, test patterns
get_config	Database, auth framework, assets, cache, queue, Action Cable
get_gems	Notable gems with versions, categories, config file locations
get_env	Environment variables + credentials keys (not values)
get_helper_methods	App + framework helpers with view cross-references
get_service_pattern	Interface, dependencies, side effects, callers
get_job_pattern	Queue, retries, guard clauses, broadcasts, schedules
get_component_catalog	ViewComponent/Phlex: props, slots, previews, sidecar assets

</details> <details open> <summary><strong>Data & Debugging</strong></summary>

Tool	What it does
dependency_graph	Model/service dependency graph in Mermaid or text format
migration_advisor	Migration code generation with reversibility + affected models
search_docs	Bundled topic index with weighted keyword search
query	Safe read-only SQL with timeout, row limit, column redaction
read_logs	Reverse file tail with level filtering and sensitive data redaction
diagnose	One-call error diagnosis with classification + context + git + logs
review_changes	PR/commit review with per-file context + warnings
runtime_info	Live DB pool, table sizes, pending migrations, cache stats, queue depth
session_context	Session-aware context tracking across tool calls

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All 38 tools with parameters →  |  Real-world recipes →

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Live Resources (VFS)

AI clients can also read structured data through resource templates - rails-ai-context:// URIs that introspect fresh on every request. Zero stale data.

Resource Template	What it returns
rails-ai-context://controllers/{name}	Actions, inherited filters, strong params
rails-ai-context://controllers/{name}/{action}	Action source code with applicable filters
rails-ai-context://views/{path}	View template content (path traversal protected)
rails-ai-context://routes/{controller}	Live route map filtered by controller
rails://models/{name}	Per-model details: associations, validations, schema

Plus 9 static resources (schema, routes, conventions, gems, controllers, config, tests, migrations, engines) that AI clients read directly.

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Anti-Hallucination Protocol

Every generated context file ships with 6 rules that force AI verification before writing code. The protocol targets the exact cognitive failures that produce confident-wrong code: statistical priors overriding observed facts, pattern completion beating verification, stale context lies.

<details> <summary><strong>The 6 rules (shown to AI in every CLAUDE.md / .cursor/rules / .cursorrules / .github/instructions)</strong></summary> <br>

1. Verify before you write. Never reference a column, association, route, helper, method, class, partial, or gem not verified in THIS project via a tool call in THIS turn. Never invent names that "sound right."
2. Mark every assumption. If proceeding without verification, prefix with [ASSUMPTION]. Silent assumptions forbidden. "I'd need to check X first" is a preferred answer.
3. Training data describes average Rails. This app isn't average. When something feels "obviously" standard Rails, query anyway. Check rails_get_conventions + rails_get_gems BEFORE scaffolding.
4. Check the inheritance chain before every edit. Inherited before_action filters, concerns, includes, STI parents. Inheritance is never flat.
5. Empty tool output is information, not permission. "0 callers found" signals investigation, not license to proceed on guesses.
6. Stale context lies. Re-query after writes. Earlier tool output may be wrong after edits.

Enabled by default. Disable with config.anti_hallucination_rules = false if you prefer your own rules.

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How it works

graph TD
    A["Your Rails App\nmodels + schema + routes + controllers + views + jobs"] -->|"39 introspectors"| B

    B["rails-ai-context\nPrism AST parsing · Cached · Confidence-tagged\nVFS: rails-ai-context:// URIs introspected fresh"]

    B --> C["MCP Server\nstdio / HTTP\n38 tools · 5 templates"]
    B --> D["CLI Tools\nRake / Thor\nSame 38 tools"]
    B --> E["Static Files\nCLAUDE.md · .cursor/rules/ · .cursorrules\n.github/instructions/"]

    style A fill:#4a9eff,stroke:#2d7ad4,color:#fff
    style B fill:#2d2d2d,stroke:#555,color:#fff
    style C fill:#0984e3,stroke:#0770c2,color:#fff
    style D fill:#00cec9,stroke:#00b5b0,color:#fff
    style E fill:#a29bfe,stroke:#8c83f0,color:#fff

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Install

Option A - In Gemfile:

gem "rails-ai-context", group: :development
rails generate rails_ai_context:install

Option B - Standalone (no Gemfile entry needed):

gem install rails-ai-context
cd your-rails-app
rails-ai-context init

Both paths ask which AI tools you use (Claude Code, Cursor, GitHub Copilot, OpenCode, Codex CLI) and whether you want MCP or CLI mode. Each tool gets its own MCP config file - auto-detected on project open.

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Commands

In-Gemfile	Standalone	What it does
rails ai:context	rails-ai-context context	Generate context files
rails 'ai:tool[NAME]'	rails-ai-context tool NAME	Run any of the 38 tools
rails ai:tool	rails-ai-context tool --list	List all available tools
rails ai:serve	rails-ai-context serve	Start MCP server (stdio)
rails ai:doctor	rails-ai-context doctor	Diagnostics + AI readiness score
rails ai:watch	rails-ai-context watch	Auto-regenerate on file changes

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Documentation

Quickstart	5-minute getting started
Tools Reference	All 38 tools with every parameter
Recipes	Real-world workflows and examples
Custom Tools	Build and test your own MCP tools
Configuration	40+ config options with defaults
AI Tool Setup	Claude, Cursor, Copilot, OpenCode, Codex
Architecture	System design and internals
Introspectors	All 39 introspectors and AST engine
Security	4-layer SQL safety and file blocking
CLI Reference	Commands and argument syntax
Standalone	Use without Gemfile entry
Troubleshooting	Common issues and fixes
FAQ	Frequently asked questions

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Build your own tools

Register custom MCP tools alongside the 38 built-in ones:

# app/mcp_tools/rails_get_business_metrics.rb
class RailsGetBusinessMetrics < MCP::Tool
  tool_name "rails_get_business_metrics"
  description "Key business metrics for this app"

  def call(period: "week")
    MCP::Tool::Response.new([{ type: "text", text: "Users this #{period}: #{User.recent.count}" }])
  end
end

# config/initializers/rails_ai_context.rb
config.custom_tools = [RailsGetBusinessMetrics]

Test with the built-in TestHelper (works with RSpec and Minitest):

include RailsAiContext::TestHelper

response = execute_tool("business_metrics", period: "month")
assert_tool_response_includes(response, "Users")

Custom Tools Guide →

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Configuration

# config/initializers/rails_ai_context.rb
if defined?(RailsAiContext)
  RailsAiContext.configure do |config|
    config.ai_tools   = %i[claude cursor] # Which AI tools to generate for
    config.tool_mode  = :mcp              # :mcp (default) or :cli
    config.preset     = :full             # :full (39 introspectors) or :standard (17)
  end
end

All 40+ configuration options →

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Observability

Every MCP tool call fires an ActiveSupport::Notifications event:

ActiveSupport::Notifications.subscribe("rails_ai_context.tools.call") do |event|
  Rails.logger.info "[MCP] #{event.payload[:method]} - #{event.duration}ms"
end

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Requirements

• Ruby >= 3.2    Rails >= 7.1
• Optional: brakeman for security scanning, listen for watch mode, ripgrep for fast search

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About

Built by a Rails developer with 10+ years of production experience.<br> 2154 tests + 100-example e2e harness. 38 tools. 5 resource templates. 39 introspectors. Standalone or in-Gemfile.<br> MIT licensed. Contributions welcome.

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If this gem saves you time, consider sponsoring the project.

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