Borrowing it
Nothing to install: this file belongs to levifig/rails-instructions. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/levifig/rails-instructions/main/.github/instructions/rails-api.instructions.mdgit 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/instructions/levifig/rails-instructions/rails-api)<a href="https://agentmods.dev/instructions/levifig/rails-instructions/rails-api"><img src="https://agentmods.dev/badge/instructions/levifig/rails-instructions/rails-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/instructions/levifig/rails-instructions/rails-api"><img src="https://agentmods.dev/badge/instructions/levifig/rails-instructions/rails-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 | $0.01051 | $0.01051 |
| Opus 5.5 | $0.00420 | $0.00420 |
| Sonnet 5.5 | $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 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 — 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.
- 1mo 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 (56 stars, last pushed 1y ago), licensed MIT. It adds 1,051 tokens to every session, about $0.0042 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.
Other instructions, from other repositories
vscode buildNext.instructions.md
Working notes and architecture documentation for the new esbuild-based build system in build/next. Use when making changes to the new build pipeline (transpile/bundle commands, NLS plugin, source-map handling, resource copying, or self-hosting watch tasks).
next.js AGENTS.md
AGENTS.md instructions for vercel/next.js, covering next.js development guide, codebase structure, monorepo overview, core package: packages/next and other important packages.
vscode oss-third-party-notices.instructions.md
Instructions for microsoft/vscode, covering vs code oss third-party-notices pipeline, architecture, pipeline flow in ci, cache eligibility and rollout and applying the notice (cutover).
langchain AGENTS.md
AGENTS.md instructions for langchain-ai/langchain, covering global development guidelines for the langchain monorepo, corridor security analysis, project architecture and context, monorepo structure and development tools & commands.
vscode copilot-instructions.md
Copilot instructions for microsoft/vscode, covering vs code copilot instructions, project overview, root folders, core architecture (src/ folder) and built-in extensions (extensions/ folder).
deno copilot-instructions.md
Copilot instructions for denoland/deno, covering deno development guide for github copilot, network access, high level overview, key directories and key files to understand first.