How does Atlas ensure my Astro refactor doesn't break existing code?

Atlas first maps all public symbols and their callsites using `lsp findReferences`. It then pins behavior by running your `vitest` tests with `bash pnpm test` before any changes, and re-runs them after each modification, ensuring no regressions in your Astro project.

Can Atlas refactor `.astro` components and content collections?

Yes, Atlas works across `.astro` islands, content collections defined in `src/content.config.ts`, and `src/pages` routes. It understands Astro's zero-JS-by-default rendering model and can even add Zod schemas to content collections.

How does Atlas handle formatting after refactoring Astro code?

Atlas integrates with `prettier (prettier-plugin-astro)`. After applying structural changes, Atlas can prompt to format the modified Astro files, ensuring your codebase remains consistent with your project's formatting standards.

What if an Astro file changes while Atlas is working on a refactor?

Atlas uses `apply_patch`, which anchors on context lines. If an Astro file has drifted from its original state, `apply_patch` will fail with 'Failed to find context', preventing unintended changes to a file that has been modified externally.

Does Atlas keep my Astro code local?

Yes, Atlas can build its code index with local Ollama embeddings, keeping your Astro project code off third-party servers. This ensures your sensitive code remains within your local environment.

How do I review changes Atlas makes to my Astro project?

Atlas computes a unified diff for every file edit, such as changes to `astro.config.mjs` or `.astro` components, and surfaces it for your approval before writing. This gives you full control and transparency over all modifications.

Can Atlas help with Astro content collection schemas?

Yes, Atlas can add a Zod schema to a content collection in `src/content.config.ts` and run `astro check` behind a permission prompt. This helps you maintain data integrity and validate your content collections effectively.

Refactor a legacy module in Astro with Atlas in 2026

Atlas empowers Astro developers in 2026 to refactor legacy modules by leveraging `vitest` for behavior pinning, `pnpm` for dependency management, and `prettier (prettier-plugin-astro)` for consistent formatting, ensuring structural changes do not break existing functionality or callers.

How to map Astro module surfaces and callers with Atlas

In 2026, refactoring an Astro module begins by understanding its public surface. Atlas uses the `lsp` tool's `documentSymbol` operation to map all exported symbols from your `.astro` components or `src/content.config.ts` schemas, providing a comprehensive view of 100% of the module's external API.

To safely restructure an Astro module, you must first identify its public interface and every location where it is used. Atlas achieves this by connecting to Model Context Protocol servers and exposing their tools. You can instruct Atlas to use the `lsp` tool's `documentSymbol` operation on your target `.astro` component, `src/content.config.ts` content collection schema, or any other relevant Astro file. This action enumerates all exported symbols. Following this, Atlas can execute `lsp findReferences` on each identified symbol, meticulously listing every callsite across your Astro project. This crucial first step ensures that Atlas, and you, have a complete understanding of the module's dependencies before any modifications begin, preventing silent breakage at unknown callsites.

How to pin Astro module behavior with `vitest` and Atlas

Before any refactoring in Astro, it is crucial to pin the module's existing behavior. Atlas achieves this by running your `vitest` test suite with the `bash` tool, recording a green baseline of 0 failures, ensuring that subsequent changes do not introduce regressions.

A core principle of safe refactoring is to establish a reliable baseline of expected behavior. For Astro projects, this means running your `vitest` test suite. Atlas integrates directly with your terminal environment through the `bash` tool. You can command Atlas to execute `pnpm test` (or your specific `vitest` command) to run all existing tests. Atlas will record the output, confirming that all tests pass and establishing a 'green' baseline. This step is non-negotiable; it provides a safety net, allowing you to confidently make structural changes knowing that any deviation from the original behavior will be immediately flagged by a failing test. This process ensures that the job of restructuring an old module does not inadvertently change its behavior.

How to apply structural changes to Astro files with Atlas `apply_patch`

Restructuring an Astro module requires precise and safe file modifications. Atlas employs the `apply_patch` tool to make structural changes, anchoring each hunk on context lines within `.astro` files or `src/pages` routes, and refusing to apply if the file has drifted by even 1 line.

Once the module's surface is mapped and its behavior pinned, Atlas proceeds with structural changes using the `apply_patch` tool. This tool is designed for robust and context-aware file modifications. When Atlas proposes a change to an `.astro` component, a `src/pages` route, or even `astro.config.mjs`, it generates a patch that includes context lines around each modification hunk. The `apply_patch` tool then attempts to apply this patch. A critical safety feature is its refusal to apply if the target file has drifted from its expected state. If the context lines or old lines specified in the patch do not precisely match the current file content, `apply_patch` will fail with a 'Failed to find context' error. This prevents Atlas from making changes to a file that has been modified externally, ensuring that every edit is applied against the intended version of the code.

How to iteratively test Astro refactors with Atlas and `vitest`

To prevent silent breakage during an Astro refactor, Atlas advocates for iterative testing. After each `apply_patch` hunk lands, Atlas re-runs your `vitest` tests using the `bash` tool, ensuring that the module's behavior remains consistent and 100% functional throughout the process.

Refactoring is an iterative process, and continuous validation is key to success. Instead of making all changes and then testing once at the end, Atlas re-runs your `vitest` tests after each significant modification. After `apply_patch` successfully lands a hunk of changes to an `.astro` file or a content collection schema, Atlas will automatically execute `atlas bash pnpm test` again. This immediate feedback loop is invaluable. If a change introduces a regression, you will know instantly, allowing for quick correction before further modifications compound the issue. This approach significantly reduces the risk of silent breakage and ensures that the module's behavior remains unchanged, even as its internal structure evolves.

How to track Astro call sites and migration progress with Atlas `todowrite`

Managing the migration of callers during an Astro module refactor is critical. Atlas uses the `todowrite` tool to track remaining callsites identified by `lsp`'s `findReferences`, ensuring that no more than 0 unmigrated references are left when the refactor is complete.

When refactoring a module, especially one with many callers, it is essential to keep track of which callsites have been updated and which still need attention. Atlas addresses this with the `todowrite` tool. After using `lsp findReferences` to enumerate all callers of a legacy Astro module, Atlas can populate a `todowrite` list with these references. As you migrate each callsite, perhaps by updating an import path in another `.astro` component or adjusting a prop in a `src/pages` route, Atlas can mark that item as complete. This provides a clear, persistent record of progress, preventing a partially migrated module from being mistaken for a finished one and ensuring that all callers are eventually updated to reflect the new module structure.

How to review and approve Atlas changes in Astro projects

Every change Atlas proposes for your Astro project is subject to your explicit approval. Atlas computes a unified diff for each file edit, such as modifications to `astro.config.mjs` or `.astro` components, and surfaces it for review before writing, offering 100% transparency.

Atlas operates with a strong emphasis on user control and transparency. Before any change is written to your Astro project's filesystem, Atlas presents a unified diff for your review. Whether it is a modification to an `.astro` component, an update to `src/content.config.ts`, or a change to `astro.config.mjs`, you will see exactly what Atlas intends to do. This diff is rendered in Atlas's terminal-native TUI, which uses SolidJS through the OpenTUI renderer, often with a charcoal-and-blue default theme. You have the option to approve, reject, or request further modifications. This permission-gated approach ensures that you maintain full oversight of the refactoring process, allowing you to verify that the changes align with your intentions and do not introduce any unintended side effects.

Step by step

01Map the Astro module's public surface: Use `atlas lsp documentSymbol` on your `.astro` component or `src/content.config.ts` schema, then `atlas lsp findReferences` on each exported symbol to enumerate all callsites.
02Pin existing Astro behavior: Run your `vitest` tests with `atlas bash pnpm test` and record the green baseline before any changes.
03Apply structural changes to Astro files: Use `atlas apply_patch` to restructure `.astro` components or `src/pages` routes, ensuring context lines match.
04Re-run Astro tests iteratively: After each `apply_patch` hunk, execute `atlas bash pnpm test` to verify behavior immediately.
05Track remaining Astro callsites: Update the `todowrite` list with any unmigrated references identified by `lsp findReferences`.
06Review and approve Astro file edits: Examine the unified diff presented by Atlas for changes to `.astro` files or `astro.config.mjs` before writing.
07Format Astro code with `prettier`: After changes, let Atlas format the modified files using `prettier (prettier-plugin-astro)` via a permission prompt.
08Commit Astro changes: Use Atlas to stage and create a git commit for the refactored module, leveraging its git integration.

Frequently asked questions

How does Atlas ensure my Astro refactor doesn't break existing code?: Atlas first maps all public symbols and their callsites using `lsp findReferences`. It then pins behavior by running your `vitest` tests with `bash pnpm test` before any changes, and re-runs them after each modification, ensuring no regressions in your Astro project.
Can Atlas refactor `.astro` components and content collections?: Yes, Atlas works across `.astro` islands, content collections defined in `src/content.config.ts`, and `src/pages` routes. It understands Astro's zero-JS-by-default rendering model and can even add Zod schemas to content collections.
How does Atlas handle formatting after refactoring Astro code?: Atlas integrates with `prettier (prettier-plugin-astro)`. After applying structural changes, Atlas can prompt to format the modified Astro files, ensuring your codebase remains consistent with your project's formatting standards.
What if an Astro file changes while Atlas is working on a refactor?: Atlas uses `apply_patch`, which anchors on context lines. If an Astro file has drifted from its original state, `apply_patch` will fail with 'Failed to find context', preventing unintended changes to a file that has been modified externally.
Does Atlas keep my Astro code local?: Yes, Atlas can build its code index with local Ollama embeddings, keeping your Astro project code off third-party servers. This ensures your sensitive code remains within your local environment.
How do I review changes Atlas makes to my Astro project?: Atlas computes a unified diff for every file edit, such as changes to `astro.config.mjs` or `.astro` components, and surfaces it for your approval before writing. This gives you full control and transparency over all modifications.
Can Atlas help with Astro content collection schemas?: Yes, Atlas can add a Zod schema to a content collection in `src/content.config.ts` and run `astro check` behind a permission prompt. This helps you maintain data integrity and validate your content collections effectively.

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