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/api)<a href="https://agentmods.dev/rules/levifig/rails-instructions/api"><img src="https://agentmods.dev/badge/rules/levifig/rails-instructions/api/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/api"><img src="https://agentmods.dev/badge/rules/levifig/rails-instructions/api.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 | $0.01055 |
| Opus 5.5 | $0.00000 | $0.00422 |
| Sonnet 5.5 | $0.00000 | $0.00211 |
| Haiku 4.5 | $0.00000 | $0.00105 |
Grade A, and why
api 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 — 213 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Rails API Guide
Core Philosophy
- Design APIs for longevity and stability
- Version from the very beginning
- Keep responses consistent and predictable
- Document thoroughly and accurately
- Build APIs that developers love to use
API Design Principles
- Follow RESTful conventions strictly
- Use standard HTTP methods appropriately
- Return meaningful status codes
- Keep endpoints focused and simple
- Design for future extensibility
Versioning Strategy
- Version APIs from day one
- Use URL path versioning (/api/v1)
- Never break backward compatibility
- Deprecate gracefully with notices
- Document version differences clearly
Request Handling
- Accept JSON by default
- Support content negotiation
- Validate request formats
- Handle malformed requests gracefully
- Provide clear error messages
Response Format
- Use consistent JSON structure
- Include metadata when helpful
- Implement sparse fieldsets
- Support response filtering
- Keep payloads minimal
Authentication Methods
- Use token-based authentication
- Implement OAuth when appropriate
- Support API keys for simple cases
- Never use session cookies for APIs
- Document authentication clearly
Authorization Patterns
- Check permissions for every endpoint
- Use consistent authorization logic
- Return proper 401/403 status codes
- Implement role-based access
- Audit API access patterns
Error Handling
- Return consistent error format
- Include error codes and messages
- Provide debugging information in development
- Log errors appropriately
- Handle exceptions gracefully
Status Codes
- Use standard HTTP status codes correctly
- 200 OK for successful GET/PUT
- 201 Created for successful POST
- 204 No Content for successful DELETE
- 422 Unprocessable Entity for validation errors
Pagination
- Always paginate list endpoints
- Use consistent pagination format
- Include total count and page info
- Support customizable page sizes
- Consider cursor-based pagination
Rate Limiting
- Implement rate limiting from start
- Return rate limit headers
- Use progressive throttling
- Provide higher limits for authenticated users
- Document rate limits clearly
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 · 213 lines · 0 tokens per session scan A d4cc57ccb790
api 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 1,055 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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