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feat: define thoughtbot rules for AI-enabled IDEs #764

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feat: define Thoughtbot rules for AI-enabled IDEs
laicuRoot Jul 25, 2025
cddf211
prefer classes over modules
laicuRoot Sep 26, 2025
78827e4
use Rspec unless minitest is present
laicuRoot Sep 26, 2025
e86908e
do not make premature suggestions about queries
laicuRoot Sep 26, 2025
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31 changes: 31 additions & 0 deletions rails/ai-rules/rails-rules.md
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# IDE AI thoughtbot rules

You are an expert in Ruby on Rails, PostgreSQL, and Hotwire (Turbo and Stimulus).

## Key Conventions

- Follow RESTful routing conventions: Seven restful actions: index, show, new, create, edit, update, delete ([thoughtbot post REST-ish routing guide](https://thoughtbot.com/blog/in-relentless-pursuit-of-rest-ish-routing))
- Prefer classes to modules when designing functionality that is shared by multiple models.

## Data / Models

- To find model structure look in `db/schema.rb`
- When working with model attributes don’t guess, grep the schema at `db/schema.rb` to confirm and use only valid attributes

## UI and Styling

- Use Rails view helpers and partials to keep views DRY

## Performance Optimization

- Always check for N+1 queries when rendering collections
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@louis-antonopoulos louis-antonopoulos Jan 9, 2026 •
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I would remove or change this line. I think it's more beneficial to use a tool like Bullet or Rails' strict_loading and rely on tests failing because of N+1 violations, which then guide the agent to fixing the issue.

I say this because there's a balance between telling the agent too little and too much, and I see this instruction as an opportunity cost:

"What might the agent not listen to because it was focused on this instruction, an issue that we have simple ways to check for?"

So while I would remove it, if kept, maybe something like

Suggested change
- Always check for N+1 queries when rendering collections
- Avoid N+1 queries when rendering collections

- Prefer includes for eager loading

## Testing

- Always write tests to cover new code generated
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@MatheusRich MatheusRich Sep 19, 2025

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Should we tell it to write tests first? I think @JoelQ had more success with that.

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@laicuRoot laicuRoot Sep 26, 2025

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I have struggled with this one personally when working with Cursor. Normally I will write some basic tests, and based on that, I would get a much better suggestion for the feature and then iterate. After having the firsts tests, the tests examples that come after are good.

@JoelQ do you have any suggestions about how to make the rules effective to follow TDD?

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@JoelQ JoelQ Sep 26, 2025

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I've usually done that with an initial prompt. Zed's agent (using Claude) does this well.

- Use RSpec for testing framework, unless the project already uses minitest
- Use factories ([FactoryBot](https://thoughtbot.github.io/factory_bot/))
- In tests, avoid lets and before (avoid mystery guests), do test setup within each test
- Verify new code by running test files using `bundle exec rspec spec/path/to/file_spec.rb`
- You can run a specific test by appending the line number (it can be any line number starting from the "it" block of the test) eg. `bundle exec rspec spec/path/to/file_spec.rb:72`