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.
npx agentmods add instructions/levifig/rails-instructions/rails-apigit clone --depth 1 https://github.com/levifig/rails-instructionsWhat 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 | $0.01051 | $0.01051 |
| Opus 5 | $0.00526 | $0.00526 |
| Sonnet 5 | $0.00210 | $0.00210 |
| Haiku 4.5 | $0.00105 | $0.00105 |
Grade A, and why
rails-instructions rails-api.instructions.md 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 3d 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 — 241 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
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.
- 3d ago First seen · 241 lines · 1,051 tokens per session scan A 18a5a9705976
rails-instructions rails-api.instructions.md is an instructions file published in the GitHub repository levifig/rails-instructions (54 stars, last pushed 1y ago), licensed MIT. It adds 1,051 tokens to every session, about $0.0053 per session on Opus 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.
Other instructions, from other repositories
claude-code-settings copilot-instructions.md
Instructions for feiskyer/claude-code-settings, covering claude.md, environment setup, required dependencies, configuration and skills.
agent-rules testing.instructions.md
Instructions for lirantal/agent-rules, covering testing guidelines for node.js applications, general testing principles, guiding principles, descriptive test naming (three-part structure) and structure tests by the aaa pattern.
apex-accelerator no-interactive-shell.instructions.md
Prevents interactive shell prompts and long-output terminal replays from being injected into chat. Forbids -i flags on mv/rm/cp, read -p, and confirm prompts (incl. inside bash -c '...'). Pipe long output to files. Scoped to chat-context-loaded files; skill references/ and templates/ are exempt because they hold…
apex-accelerator github-actions.instructions.md
Project-specific standards for GitHub Actions workflows in this repository.
apex-accelerator iac-terraform-best-practices.instructions.md
Terraform-specific IaC best practices for Azure templates. AVM-first, CAF naming, security baseline, provider pins.
apex-accelerator instructions.instructions.md
Guidelines for creating high-quality custom instruction files for GitHub Copilot.