Optimised Ruby on Rails coding conventions and guidelines

Lean Ruby Rails Copilot instructions for token efficiency.txt

---
description: 'Lean Ruby/Rails Copilot instructions for token efficiency'
applyTo: '**/*.rb'
---

# Ruby on Rails

## Must Keep

- Indentation: spaces only, 2 spaces.
- Target Ruby 3.4.7+.
- Do not add `# frozen_string_literal: true`.
- Use double-quoted Ruby strings unless single quotes are required.
- Use snake_case for methods/variables and CamelCase for classes/modules.
- Keep migrations Rails/MySQL compatible.
- Use `JSON`, not `JSONB`.
- Do not set defaults for `BLOB`, `TEXT`, `GEOMETRY`, or `JSON` columns.
- Respect user time zone handling in `application_controller.rb`.
- Format view date/time as `DD/MM/YYYY HH:MM`.
- Shared partials in `app/views/application/`; feature partials stay with features.

## Code Style

- Prefer Rails helpers/APIs over custom implementations.
- Keep controllers thin; keep business logic in models/services/query objects.
- Keep methods small; use guard clauses to reduce nesting.
- Prefer composition over inheritance.
- Use meaningful names and concise behavior-focused comments.
- Prefer `Rails.logger` over `puts`.
- Prefer `tag` over `content_tag`.

## Data and Performance

- Use strong parameters for controller writes.
- Prefer scopes/relations over array processing.
- Avoid N+1 queries (`includes` when needed).
- Add DB constraints/indexes for integrity and performance.

## Structure

- Services: `app/services`.
- Reusable query objects: `app/queries`.
- Custom validators: `app/validators`.
- Authorization: `app/policies`.

## Views and API

- Keep callbacks minimal and setup-only.
- Keep behavior out of view callbacks/inline JS.
- Build paths with `Rails.root.join(...)`.
- Use Rails predicates (`present?`, `blank?`, `any?`) and safe navigation where appropriate.
- APIs: namespace versions (`/api/v1`), return consistent status/error payloads, paginate large collections.
- Use background jobs for slow/external work.

## Testing

- Cover models/services/helpers with unit tests.
- Cover end-to-end behavior with request/system tests.
- Stub external APIs and avoid brittle timing assumptions (`sleep`).
- Test background jobs with ActiveJob helpers.