Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
git clone --depth 1 https://github.com/levifig/rails-instructionsWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/rules/levifig/rails-instructions/rails-rules)<a href="https://agentmods.dev/rules/levifig/rails-instructions/rails-rules"><img src="https://agentmods.dev/badge/rules/levifig/rails-instructions/rails-rules/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/rules/levifig/rails-instructions/rails-rules"><img src="https://agentmods.dev/badge/rules/levifig/rails-instructions/rails-rules.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.03067 | $0.03067 |
| Opus 5.5 | $0.01227 | $0.01227 |
| Sonnet 5.5 | $0.00613 | $0.00613 |
| Haiku 4.5 | $0.00307 | $0.00307 |
Grade A, and why
rails-rules scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 438 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Rails Development Rules - The Rails Way with AI Agents
Built for: Solo developer + AI agents, Linear MCP integration, maximum joy
Core Philosophy
You are building a Rails 8+ application following The Rails Way™. Code should be:
- Convention over configuration
- Database-first design
- Progressive enhancement with Hotwire
- Zero-build frontend approach
- Test-driven with Minitest
- Optimized for AI agent collaboration
- Lean, readable, and maintainable
Rails 8+ Stack Preferences
- Authentication: Rails built-in (
rails generate authentication) - Background Jobs: Solid Queue (default Rails 8)
- Caching: Solid Cache (database-backed, Redis when needed)
- WebSockets: Action Cable with Solid Cable adapter
- Database: PostgreSQL with Active Record
- Frontend: Hotwire (Turbo + Stimulus) + TailwindCSS
- Asset Pipeline: Propshaft (simpler, no-build approach)
- Testing: Minitest with fixtures (no RSpec, no factories)
- Rich Text: Action Text for content editing
- File Uploads: Active Storage with direct uploads
- Deployment: Kamal with Docker
- Code Quality: StandardRB for linting/formatting
- Development Tools: Bullet gem for N+1 detection, Annotate gem for schema docs
- Error Tracking: Rails built-in error reporter
Detailed Guides
This document provides core principles. For detailed implementation guidance, see:
- core.md - Rails 8 conventions and patterns
- models.md - Active Record patterns and best practices
- controllers.md - Controller design and RESTful patterns
- services.md - Service objects and business logic
- testing.md - Testing philosophy and Minitest patterns
- security.md - Security best practices and authorization
- performance.md - Database optimization and caching
- api.md - API design and versioning (when needed)
- importmaps.md - JavaScript without build steps
- hotwire.md - Turbo & Stimulus patterns
- views.md - View helpers and rendering
- styling.md - TailwindCSS integration
- background-jobs.md - Solid Queue configuration
- deployment.md - Kamal deployment guide
- mobile.md - Hotwire Native for mobile apps (optional)
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 1mo ago First seen · 438 lines · 3,067 tokens per session scan A 336d6087ac62
rails-rules is a cursor rule published in the GitHub repository levifig/rails-instructions (56 stars, last pushed 1y ago), licensed MIT. It adds 3,067 tokens to every session, about $0.0123 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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