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 rules/levifig/rails-instructions/servicesgit 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 | $0.00000 | $0.00956 |
| Opus 5 | $0.00000 | $0.00478 |
| Sonnet 5 | $0.00000 | $0.00191 |
| Haiku 4.5 | $0.00000 | $0.00096 |
Grade A, and why
services 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 2d 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 — 165 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Rails Service Objects Guide
Core Philosophy
- Service objects encapsulate complex business operations
- Keep services focused on single responsibilities
- Make services easy to test and understand
- Use services to keep models and controllers thin
- Design for reusability and composability
When to Use Service Objects
- Complex operations spanning multiple models
- External API integrations
- Multi-step processes with transactions
- Business logic that doesn't fit naturally in models
- Operations requiring detailed error handling
- Background job processing logic
Service Design Principles
- One service, one responsibility
- Clear, descriptive naming that explains the operation
- Consistent interface across services
- Explicit dependencies and parameters
- Predictable return values and error handling
Naming Conventions
- Use verb-based names that describe the action
- Include the domain context in the name
- Examples:
UserRegistrationService,PaymentProcessor,OrderFulfillment - Keep names specific and intention-revealing
- Avoid generic names like
UserService
Service Structure
- Include ActiveModel modules for validations when needed
- Define clear public interface
- Keep implementation details private
- Use dependency injection for testability
- Document complex logic thoroughly
Input Handling
- Validate inputs early and clearly
- Use ActiveModel::Attributes for parameter handling
- Define explicit attribute types
- Provide meaningful validation messages
- Handle optional parameters gracefully
Return Values
- Return consistent, predictable results
- Use success/failure pattern for operations
- Include relevant data in responses
- Provide clear error information
- Consider using Result objects for complex returns
Error Handling
- Anticipate and handle expected failures
- Use exceptions for unexpected errors
- Provide actionable error messages
- Log errors with appropriate context
- Design for graceful degradation
Transaction Management
- Wrap related database changes in transactions
- Handle rollbacks appropriately
- Keep transactions as short as possible
- Document transaction boundaries
- Test rollback scenarios
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.
- 2d ago First seen · 165 lines · 0 tokens per session scan A fb095da4bf55
services is a cursor rule published in the GitHub repository levifig/rails-instructions (54 stars, last pushed 1y ago), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 956 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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