# Onboard to an Unfamiliar Remix Codebase with Atlas in 2026 > Atlas helps Remix developers in 2026 build a mental model of unfamiliar codebases by understanding loaders, actions, and routes.ts without reading every file. In 2026, Atlas empowers Remix developers to rapidly build a working mental model of any unfamiliar codebase by leveraging its semantic search and code indexing capabilities, integrating directly with your vite.config.ts, routes/ structure, and vitest test suite. ## Key takeaways - Atlas indexes Remix loader and action exports using AST for deep understanding. - codebase_search semantically finds relevant Remix code in routes.ts or routes/. - glob quickly maps the Remix project's vite.config.ts and directory structure. - read and lsp allow tracing Remix data flow through loader and action definitions. - The explore subagent provides safe, read-only wide sweeps of Remix code. - todowrite captures Remix-specific insights and open questions for persistent context. ## How does Atlas understand Remix loaders and actions? Atlas, in 2026, builds its code index by parsing the Abstract Syntax Tree (AST) of your Remix project, not just blind line windows. This allows it to understand the specific roles of loader and action exports within your routes.ts or routes/ directory structure. Atlas is designed to integrate deeply with Remix and React Router 7 applications. When you run Atlas in a project containing a routes.ts file or a routes/ directory, it automatically reads and indexes your loader and action exports. This AST-based indexing, powered by tree-sitter, means Atlas comprehends the data flow where loaders fetch data for a route and actions handle mutations, rather than relying on client-side state. It also understands your nested route hierarchy and ErrorBoundary components, providing a comprehensive view of how requests are handled and data is passed through your application. This foundational understanding allows Atlas to answer complex questions about data flow and component responsibilities, making it an invaluable tool for quickly grasping an unfamiliar Remix project's architecture. ## How to find Remix data flow with Atlas codebase_search? To quickly grasp data flow in an unfamiliar Remix project, Atlas's codebase_search tool, available in 2026, queries a semantic index to find relevant code snippets. For instance, you can ask how requests are authenticated, and it will return ranked results from your routes/ or routes.ts files. When faced with a new Remix codebase, the codebase_search tool is your first step. Instead of manually sifting through files, you can ask a plain-language question like "how are requests authenticated?" or "where does the user profile data load?". Atlas searches its hybrid semantic and keyword index, fused by reciprocal rank fusion, to identify the most relevant code snippets and their file paths. This means you're not just searching for keywords, but for the meaning behind your query, directly pinpointing the loader functions or action handlers responsible for those operations within your Remix application. This capability is crucial for understanding how data arrives with the document and how forms are progressively enhanced, without needing to read every single routes.ts or routes/ module. ## How to understand Remix project layout with Atlas glob? In 2026, after an initial semantic search, Atlas's glob tool helps Remix developers understand the project's physical layout. Running glob on top-level directories reveals the package structure and naming conventions, such as how routes/ are organized or where vite.config.ts resides, before you open any files. Understanding the physical layout of a Remix project is vital for building a mental model. After using codebase_search to identify key functional areas, the glob tool provides an overview of the directory shape and naming conventions. You can run glob on the top-level directories to quickly see how packages are organized, where configuration files like vite.config.ts are located, and how the routes/ directory is structured. This helps you identify patterns, such as whether routes are co-located with components or if there's a specific module for utilities. This step is particularly useful in Remix, where the file system routing in routes/ dictates much of the application's structure, allowing you to infer routing logic and component relationships without deep dives into individual files. ## How to follow Remix data flow with Atlas read and lsp? After identifying key files, Atlas's read tool allows Remix developers to inspect the top two or three most relevant files, such as a routes.ts module, in 2026. Following this, the lsp tool's goToDefinition operation helps trace imports and function calls, like those within a loader or action, to build a detailed data flow understanding. Once codebase_search has provided ranked file paths and glob has given you the project layout, it's time to dive into the code that matters. The read tool allows you to pull only the two or three files that Atlas ranked highest, preventing information overload. For a Remix project, these might be a central routes.ts file, a specific route module within routes/, or a vite.config.ts file. After reading these initial files, the lsp tool becomes invaluable. Using its goToDefinition operation, you can follow imports and function calls directly from within the terminal. This means you can trace how a loader fetches data from a utility function, or how an action interacts with a service layer, building a precise mental model of the data flow and dependencies without having to manually work through the file system or open an IDE. ## How does Atlas ensure safe exploration of Remix code? Atlas ensures safe exploration of unfamiliar Remix codebases in 2026 by delegating wide sweeps to the explore subagent, which operates with a deny-by-default permission set. This subagent can only grep, glob, read, bash, webfetch, and websearch, preventing any accidental modifications to your routes/ or vite.config.ts files. When exploring a large or complex Remix codebase, it's crucial to avoid unintended changes. Atlas addresses this by fanning out work to subagents, specifically the explore subagent, which is permissioned as read-only. This subagent is defined with a deny-by-default permission set, meaning it can only execute a limited set of safe operations: grep for pattern matching, glob for directory structure, read for file content, bash for safe shell commands, webfetch for external data, and websearch for documentation. This strict permissioning ensures that while the explore subagent can perform wide sweeps across your Remix project, examining routes/ modules, vite.config.ts, or vitest configurations, it cannot modify any files or introduce changes. This read-only guarantee provides peace of mind, allowing you to freely investigate the codebase without risk. ## How to record Remix learning and open questions with Atlas? As you build a mental model of a Remix codebase in 2026, Atlas's todowrite tool allows you to record what you've learned and any open questions. This ensures that insights about loaders, actions, or vitest configurations are captured, surviving into your next turn and preventing loss of context during complex onboarding tasks. Onboarding to an unfamiliar Remix codebase involves accumulating many small pieces of information and identifying areas that require further investigation. The todowrite tool in Atlas is designed to capture these insights. As you discover how a specific loader functions, or identify a pattern in your routes/ directory, you can immediately record it. Similarly, if you encounter an action that's unclear or a vitest setup that needs more understanding, you can add it as an open question. This ensures that your evolving mental model and any pending tasks are explicitly documented within your Atlas session, preventing context loss and allowing you to pick up exactly where you left off, even across multiple sessions. This structured note-taking is essential for effective and efficient onboarding. ## Steps 1. Ask Atlas about Remix data flow: Use codebase_search to ask a plain-language question about how data flows in the Remix app, for example: "atlas codebase_search 'how are requests authenticated in the Remix loader functions?'" 2. Map the Remix project layout: Run glob on the top-level directories to understand the routes/ structure, vite.config.ts location, and overall package layout: "atlas glob '*/'" 3. Inspect key Remix files: read the top two or three files identified by codebase_search, focusing on routes.ts or specific routes/ modules: "atlas read " 4. Trace Remix imports and definitions: Use the lsp tool's goToDefinition operation to follow imports and function calls within loader or action exports: "atlas lsp goToDefinition " 5. Delegate wide Remix code sweeps: Use the task tool to launch an explore subagent for broader investigations, ensuring it's read-only: "atlas task explore 'grep for all loader functions that access a database in routes/'" 6. Record Remix insights: Document your findings about loaders, actions, or vitest configurations using todowrite to capture learnings and open questions: "atlas todowrite 'Discovered user authentication happens in app/routes/auth.ts loader.'" ## FAQ ### How does Atlas handle Remix's file system routing? Atlas is designed to understand Remix's file system routing. It automatically reads your routes.ts or routes/ directory structure, indexing the nested route hierarchy. This allows Atlas to comprehend how URLs map to loader and action exports, providing a clear picture of your application's navigation and data handling without manual configuration. ### Can Atlas help me understand Remix ErrorBoundary components? Yes, Atlas indexes ErrorBoundary components within your Remix project. By understanding their AST declarations, Atlas can help you locate and understand how errors are handled across your application, providing insights into the error propagation and recovery mechanisms defined in your Remix routes. ### How does Atlas ensure I don't accidentally change Remix code? Atlas prioritizes safety. Every tool call is permission-gated, and it drafts a plan in a read-only agent before switching to a build agent. For wide explorations, the explore subagent is strictly deny-by-default, only allowing read-only operations like grep and glob, ensuring your Remix routes/ and vite.config.ts files remain untouched. ### Does Atlas integrate with Remix's vitest setup? Absolutely. Atlas recognizes vitest as the test runner for Remix projects. It can be instructed to add new vitest tests, for example, to cover a new Form action with progressive enhancement. After making code changes, Atlas can even run prettier across the touched route modules to maintain code style. ### Can Atlas help me refactor a client-side fetch to a Remix loader? Yes, Atlas can assist with this common Remix refactoring. You can ask Atlas to move a client-side fetch operation into a loader function. Atlas will understand the context, propose the necessary code changes within your routes/ module, and present a unified diff for your approval before writing the changes. ### What if my Remix project uses pnpm for package management? Atlas is compatible with pnpm, the package manager commonly used in Remix projects. While Atlas itself doesn't directly manage pnpm commands, its bash tool can execute any pnpm command you specify, such as pnpm install or pnpm test, allowing you to integrate your existing workflow direct. ### How does Atlas handle code formatting with prettier in Remix? Atlas integrates with prettier, the standard formatter for Remix. After Atlas makes any edits to your Remix route modules or other files, it can be instructed to run prettier across the touched files. This ensures that all code changes adhere to your project's formatting standards, maintaining consistency. --- Canonical HTML: https://runatlas.sh/resources/stacks/onboard-to-an-unfamiliar-codebase-in-remix Source of truth: aeo_pages row `/resources/stacks/onboard-to-an-unfamiliar-codebase-in-remix` (segment: Stacks) (this file is generated from it, never hand-edited). Licence: Atlas is proprietary with a free core. It is not open source and there is no public source repository.