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/controllers)<a href="https://agentmods.dev/rules/levifig/rails-instructions/controllers"><img src="https://agentmods.dev/badge/rules/levifig/rails-instructions/controllers/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/controllers"><img src="https://agentmods.dev/badge/rules/levifig/rails-instructions/controllers.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 | $0.00000 | $0.00948 |
| Opus 5.5 | $0.00000 | $0.00379 |
| Sonnet 5.5 | $0.00000 | $0.00190 |
| Haiku 4.5 | $0.00000 | $0.00095 |
Grade A, and why
controllers 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 — 164 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Rails Controllers Guide
Core Philosophy
- Controllers handle HTTP requests and responses only
- Keep controllers thin and focused
- Business logic belongs in models or service objects
- Follow RESTful conventions strictly
- Design for clarity and maintainability
Controller Design Principles
- One controller per resource
- Seven standard RESTful actions maximum
- Keep actions focused on single responsibilities
- Handle multiple response formats gracefully
- Maintain consistent patterns across controllers
RESTful Actions
- Use only standard actions when possible: index, show, new, create, edit, update, destroy
- Add custom actions sparingly and thoughtfully
- Name custom actions with clear verbs
- Group related actions in the same controller
- Consider splitting into multiple resources instead of custom actions
Before Actions
- Use before_action for common setup tasks
- Keep filter methods private
- Order filters from general to specific
- Document filter purposes when not obvious
- Avoid complex logic in filters
Strong Parameters
- Always use strong parameters for user input
- Define parameter methods as private
- Be explicit about permitted attributes
- Handle nested attributes appropriately
- Document complex parameter structures
Response Handling
- Support multiple formats (HTML, JSON, Turbo Stream)
- Use consistent status codes
- Provide meaningful error messages
- Handle missing records gracefully
- Implement proper content negotiation
Error Handling
- Rescue specific exceptions at appropriate levels
- Provide user-friendly error messages
- Log errors with sufficient context
- Use proper HTTP status codes
- Handle errors consistently across controllers
Authentication and Authorization
- Implement authentication in ApplicationController
- Check authorization in before_action callbacks
- Fail fast with unauthorized access
- Provide clear feedback for access denied
- Keep authorization logic simple and clear
Controller Concerns
- Extract shared behavior into concerns
- Name concerns based on functionality
- Keep concerns focused and cohesive
- Document concern dependencies
- Test concerns in isolation
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 · 164 lines · 0 tokens per session scan A 79fb754da7b5
controllers is a cursor rule published in the GitHub repository levifig/rails-instructions (56 stars, last pushed 1y ago), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 948 tokens. 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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