How do I find a specific controller action in a large Ruby on Rails application?

Use `atlas codebase_search "handle user login submission"` to semantically find relevant controllers, then `atlas grep 'def create' app/controllers/sessions_controller.rb` to pinpoint the exact action. Finally, `atlas read` the file and use `atlas lsp findReferences` to see where it's called.

Can Atlas help me locate Active Record callbacks like `before_save` or `after_create`?

Yes, Atlas excels at this. Describe the behavior, for example, `atlas codebase_search "send welcome email after user creation"`. Atlas will likely point to an `after_create` callback in your `User` model. You can then `atlas read` the model and use `atlas lsp findReferences` on the callback method.

How does Atlas handle `Bundler` dependencies when searching for code?

Atlas focuses on your application's source code within your Rails project, not directly on `Bundler` gem internals. However, if a behavior is implemented in your application code that interacts with a gem, Atlas will help you find that interaction point. For exploring gem source, you would typically use `bundle open `.

What if I only know what a feature does, but not its code name in Ruby on Rails?

This is precisely where Atlas shines. Start with `atlas codebase_search` using a natural language description of the feature, like "process credit card payments" or "generate PDF reports." Atlas's semantic index will return relevant Ruby on Rails code declarations, even if your words don't appear verbatim in the source.

Does Atlas integrate with `RSpec` for finding tests related to a behavior?

While Atlas's primary focus here is locating implementation, it can certainly help find related `RSpec` tests. After locating a behavior, you could use `atlas grep 'describe "User authentication"' spec/requests/` or `atlas codebase_search "tests for user sign-up flow"` to find relevant `RSpec` files in your `spec/` directory.

How can I ensure Atlas doesn't make unwanted changes to my Ruby on Rails codebase?

Atlas is designed with safety in mind. Every tool call is permission-gated, and any proposed code modifications are first drafted in a read-only plan. Crucially, Atlas computes a unified diff for every file edit and requires your explicit approval before writing any changes, giving you full control over your Rails project.

Locate where a behavior is implemented in Ruby on Rails with Atlas in 2026

Atlas empowers Ruby on Rails developers in 2026 to precisely locate where a behavior is implemented by combining semantic codebase search, `grep` for exact text, and the Language Server Protocol (LSP) tool for symbol graph navigation. This integrated approach helps you find the exact file and symbol responsible for a behavior, even when you only know what the software does, not what the code is called, all while respecting your `config/application.rb` setup and `Bundler` dependencies.

How does Atlas find Ruby on Rails code by behavior?

In 2026, Atlas leverages its hybrid semantic and keyword retrieval system to locate Ruby on Rails behaviors, even when your query doesn't match exact code terms. It indexes your codebase by AST declarations using Tree-sitter, providing a deeper understanding than blind line windows, and can use local Ollama embeddings to keep your proprietary code off third-party servers.

When you describe a behavior to Atlas using the `codebase_search` tool, it intelligently sifts through your Ruby on Rails project. For instance, if you're looking for the code that 'handles user sign-up and sends a welcome email,' Atlas doesn't just look for those exact words. Instead, it understands the *meaning* behind your query and returns candidate declarations from your models, controllers, and even Active Record callbacks. This is particularly useful in a large Rails application where a feature might span multiple files, such as a `UsersController` action, a `User` model method, and an `ActionMailer` class. Atlas's ability to build its code index with local Ollama embeddings ensures that sensitive Rails application logic remains secure on your local machine, adhering to modern data privacy standards.

How to confirm Ruby on Rails code locations with `grep`?

To confirm a behavior's location, Atlas employs its `grep` tool, powered by `ripgrep`, offering precise text matching across your Ruby on Rails project. This tool is invaluable in 2026 for validating semantic search results, allowing you to use real regular expressions and path filters specific to your Rails directory structure, like `app/models` or `app/controllers`.

After `codebase_search` provides initial candidates for a Ruby on Rails behavior, the `grep` tool allows for granular confirmation. You can specify a regular expression to search for exact method names, variable declarations, or specific strings within your Rails codebase. For example, if `codebase_search` suggests a `User` model method, you might use `grep 'def send_welcome_email'` to find its exact definition. Atlas's `grep` tool supports `include` and `path` filters, enabling you to narrow searches to specific Rails directories, such as `app/services/` for service objects or `app/jobs/` for background jobs managed by `Active Job`. This combination of semantic and exact search ensures you pinpoint the correct code, avoiding false positives that might arise from generic terms.

How does Atlas use LSP to navigate Ruby on Rails symbols?

The Language Server Protocol (LSP) tool in Atlas provides a robust symbol graph for Ruby on Rails, allowing developers in 2026 to trace method calls and declarations with precision. This capability is crucial for understanding complex Rails behaviors, enabling you to jump directly to a symbol's definition or find all its references across your `app/` directory and `lib/` modules.

Once you've identified a promising code candidate using `codebase_search` and `grep`, Atlas's `lsp` tool becomes your guide through the Ruby on Rails symbol graph. Using the `findReferences` operation, you can see every callsite of a specific method or variable, helping you understand its impact across your application. For instance, if you've found a `before_action` callback in a `PostsController`, `lsp findReferences` can show you all controller actions that utilize it. Conversely, `workspaceSymbol` allows you to jump directly to a declaration by its name, such as `workspaceSymbol 'User#authenticate'`, providing immediate access to the method's implementation. This deep integration with the Rails symbol graph, built on AST declarations, ensures that you can navigate even the most intricate Active Record associations or custom `RuboCop` configurations with ease.

How does Atlas ensure safety and review for Ruby on Rails code changes?

Atlas prioritizes safety and developer review throughout the code location and modification process for Ruby on Rails projects in 2026. Every Atlas tool call is permission-gated, and it drafts a read-only plan before any build actions. Crucially, Atlas computes a unified diff for every proposed file edit, surfacing it for explicit approval before writing any changes to your `config/application.rb` or other critical files.

When working with a Ruby on Rails codebase, Atlas provides multiple layers of safety. Before executing any tool, such as `read` to open a file or `lsp` to modify code (if enabled), Atlas consults permission-gated rules (allow, ask, deny). This ensures you maintain control over what Atlas can do. If Atlas proposes a change, perhaps to add an `RSpec` request test or a new controller action, it first drafts a plan in a read-only agent. Only after your approval does it switch to a build agent. For every file edit, Atlas generates a unified diff, similar to what you'd see with `git diff`, allowing you to meticulously review the proposed changes to your models, views, controllers, or `Gemfile` before they are written. Atlas also snapshots file changes as git patches, so edits can be easily diffed and rolled back, providing a robust safety net for your Rails development workflow.

Step by step

01Initialize Atlas in your Ruby on Rails application by running `atlas` in the root directory containing your `config/application.rb` file. Atlas will read your models, routes, and Active Record schema.
02Describe the behavior you want to locate using `atlas codebase_search "find where user authentication is handled and redirects to dashboard"`. Atlas will return semantic candidates, potentially pointing to a `SessionsController` or `User` model method.
03Confirm the semantic results with a precise text search using `atlas grep 'def authenticate_user!' app/controllers/`. This leverages `ripgrep` to find exact method definitions within your Rails controllers.
04Open the most promising candidate file with `atlas read app/controllers/sessions_controller.rb`. Atlas will loudly fail with 'File not found' if the path is incorrect, offering 'Did you mean' suggestions.
05Use the LSP tool to explore the symbol graph: `atlas lsp findReferences 'authenticate_user!'` to see all callsites, or `atlas lsp workspaceSymbol 'User#authenticate'` to jump to the method's declaration in the `User` model.
06Summarize the call path and exact file/line references back to yourself or a teammate, for example: "The user authentication behavior is implemented in `app/controllers/sessions_controller.rb` at line 42, calling `User#authenticate` defined in `app/models/user.rb` at line 105."
07If Atlas proposes any modifications, such as adding an `RSpec` request test, review the unified diff presented by Atlas and approve or deny the changes before they are written to your Rails project.

Frequently asked questions

How do I find a specific controller action in a large Ruby on Rails application?: Use `atlas codebase_search "handle user login submission"` to semantically find relevant controllers, then `atlas grep 'def create' app/controllers/sessions_controller.rb` to pinpoint the exact action. Finally, `atlas read` the file and use `atlas lsp findReferences` to see where it's called.
Can Atlas help me locate Active Record callbacks like `before_save` or `after_create`?: Yes, Atlas excels at this. Describe the behavior, for example, `atlas codebase_search "send welcome email after user creation"`. Atlas will likely point to an `after_create` callback in your `User` model. You can then `atlas read` the model and use `atlas lsp findReferences` on the callback method.
How does Atlas handle `Bundler` dependencies when searching for code?: Atlas focuses on your application's source code within your Rails project, not directly on `Bundler` gem internals. However, if a behavior is implemented in your application code that interacts with a gem, Atlas will help you find that interaction point. For exploring gem source, you would typically use `bundle open <gem_name>`.
What if I only know what a feature does, but not its code name in Ruby on Rails?: This is precisely where Atlas shines. Start with `atlas codebase_search` using a natural language description of the feature, like "process credit card payments" or "generate PDF reports." Atlas's semantic index will return relevant Ruby on Rails code declarations, even if your words don't appear verbatim in the source.
Does Atlas integrate with `RSpec` for finding tests related to a behavior?: While Atlas's primary focus here is locating implementation, it can certainly help find related `RSpec` tests. After locating a behavior, you could use `atlas grep 'describe "User authentication"' spec/requests/` or `atlas codebase_search "tests for user sign-up flow"` to find relevant `RSpec` files in your `spec/` directory.
How can I ensure Atlas doesn't make unwanted changes to my Ruby on Rails codebase?: Atlas is designed with safety in mind. Every tool call is permission-gated, and any proposed code modifications are first drafted in a read-only plan. Crucially, Atlas computes a unified diff for every file edit and requires your explicit approval before writing any changes, giving you full control over your Rails project.

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