Atlas onboards you to an unfamiliar TypeScript codebase by starting from the type system rather than the file tree. Run atlas in a project with a tsconfig.json and Atlas reads your type definitions, path aliases, and strictness settings. codebase_search then answers a plain-language question against the semantic index, glob shows the package layout, read opens the two or three .ts files that matter, and the lsp tool's goToDefinition operation resolves an aliased import. pnpm installs, vitest runs the suites, prettier sets the formatting baseline.
How do you learn an unfamiliar TypeScript codebase without reading every file?
Atlas learns an unfamiliar TypeScript codebase in 2026 by reading tsconfig.json first, then asking codebase_search a plain-language question such as how requests are authenticated. Atlas searches code with hybrid semantic and keyword retrieval fused by reciprocal rank fusion, returning ranked .ts snippets with real file paths.
The job to be done is building a working mental model of a repository you have never seen before, without reading every file. In TypeScript the fastest route into that model is the type layer: tsconfig.json declares the strictness settings and the path aliases every import obeys, and the exported interfaces describe the contracts before any implementation does. Atlas reads your type definitions, path aliases, and strictness settings up front, so when codebase_search ranks a candidate it can hand you the exported interface and the function that satisfies it together. Atlas indexes code by AST declarations using tree-sitter, not blind line windows, so a hit is a whole type or function.
What does tsconfig.json tell Atlas about a TypeScript project?
Atlas treats tsconfig.json as the map of a TypeScript project and reads 2 things from it first. The compilerOptions describe the strictness settings the codebase is held to, and the path aliases explain why an import of @app/services resolves to a directory nowhere near the importing file.
Path aliases are the single biggest source of confusion when onboarding to someone else's TypeScript repo, because the import specifier and the on-disk path do not match. Reading tsconfig.json resolves that immediately, and the lsp tool's goToDefinition operation then jumps from an aliased import straight to the declaration. Strictness matters too: a project with strict enabled tells you the type coverage is real, while a project full of any tells you the contracts are aspirational. Running glob on the top-level directories completes the picture by showing the package layout and naming conventions, including any pnpm workspace packages that each carry their own tsconfig.json.
How does Atlas follow TypeScript types and interfaces across a repo?
Atlas follows TypeScript types across a repo with read plus the lsp tool's goToDefinition operation. Read the 2 or 3 files codebase_search ranked highest, then jump from an interface reference to its declaration, which in a typed codebase is usually the fastest description of what a subsystem promises.
Types are documentation that cannot go stale, which makes them the best onboarding surface a TypeScript codebase has. Atlas walks them directly: goToDefinition on a return type lands on the interface, goToDefinition on that interface's fields lands on the nested types, and within a few hops the shape of the subsystem is explicit. Atlas fans out work to subagents that can run in the foreground or in parallel background sessions, so a wide sweep across a large .ts tree can happen in the background while you keep reading the type definitions in front of you.
How does the explore subagent read a TypeScript repo safely?
Atlas delegates wide sweeps of a TypeScript repository to the explore subagent through the task tool. The explore subagent is defined with a deny-by-default permission set that only allows grep, glob, read, bash, webfetch, and websearch, so a sweep across your .ts files in 2026 cannot change a type definition.
Onboarding is read-heavy work, and read-heavy work is where an accidental edit does the most damage, because nobody is watching the diff yet. The explore subagent solves that structurally rather than by good intentions: grep, glob, read, bash, webfetch, and websearch are the only tools it can call. Even a bash call inside the sweep, such as a pnpm install, is checked against the same permission rules before it executes. When you do start changing code, for example to tighten types or remove any, every edit to a .ts file arrives as a diff you approve before it is written.
How do you verify a TypeScript codebase with pnpm, vitest, and prettier?
Atlas verifies a new TypeScript codebase by running the project's 3 real commands: pnpm to install, vitest to see which suites pass on a clean checkout, and prettier to learn the formatting baseline. Atlas records the remaining open questions as a todowrite list for the next session.
A clean pnpm install plus a vitest run is the most honest one-command summary of a TypeScript repo, and any failure on a fresh clone is itself onboarding documentation. prettier reveals the formatting conventions before you propose a diff that would otherwise churn unrelated lines. Once the baseline is established, ask Atlas to tighten types, remove any, or generate typed API clients, then approve the diff. The vitest specs and the strictness settings in tsconfig.json tell you how much of the .ts tree is genuinely type-safe before you commit to a mental model.
Which TypeScript files describe a project fastest?
Atlas reads 4 TypeScript files first: tsconfig.json for the strictness settings and path aliases, the exported interfaces that define the contracts, the vitest specs that exercise them, and package.json for the pnpm scripts. Types are documentation that cannot go stale, so Atlas starts there.
tsconfig.json settles two questions immediately: how strict the TypeScript codebase is, and how an aliased import maps to disk. Exported interfaces are the fastest description of a TypeScript subsystem, because an interface states the contract without the implementation noise. vitest specs show how those interfaces are used in practice, including the error branches. package.json names the pnpm scripts and the prettier check. Between tsconfig.json, the interfaces, and the vitest specs, a TypeScript repository documents itself better than most, which is why Atlas reads all three before proposing to remove any.
Step by step
- 01Run atlas in a project with a tsconfig.json and let Atlas read your type definitions, path aliases, and strictness settings.
- 02Ask codebase_search a plain-language question, for example how requests are authenticated, and review the ranked .ts snippets it returns with file paths.
- 03Run glob on the top-level directories to see the package layout and naming conventions, including workspace packages with their own tsconfig.json.
- 04Read the two or three TypeScript files codebase_search ranked highest, then resolve each aliased import with the lsp tool's goToDefinition operation.
- 05Delegate a wide sweep to the explore subagent through the task tool; its permission set only allows grep, glob, read, bash, webfetch, and websearch.
- 06Install the workspace with pnpm, then run vitest to see which suites pass on a clean checkout of the TypeScript project.
- 07Run prettier to learn the formatting baseline, then ask Atlas to tighten types or remove any and approve the diff.
- 08Record what you learned, and every open question, as a todowrite list so it survives into the next turn.
Frequently asked questions
- how do I onboard to a large TypeScript codebase quickly
- Run atlas in a project with a tsconfig.json so it reads your type definitions, path aliases, and strictness settings, then ask codebase_search a plain-language question. Read only the two or three .ts files it ranks highest.
- how do I resolve a TypeScript path alias to a real file
- Use the lsp tool's goToDefinition operation. Atlas reads the path aliases in tsconfig.json and jumps from the aliased import specifier to the declaration on disk, which the import path alone never reveals.
- can an AI agent explore a TypeScript repo without editing it
- Yes. Atlas delegates wide sweeps to the explore subagent through the task tool, and that subagent has a deny-by-default permission set allowing only grep, glob, read, bash, webfetch, and websearch.
- can Atlas remove any and tighten types in TypeScript
- Yes. Ask Atlas to tighten types, remove any, or generate typed API clients, then approve the diff. Atlas computes a unified diff for every file edit and surfaces it for approval before writing.
- does Atlas run vitest and prettier on a TypeScript project
- Yes. Atlas installs with pnpm, runs vitest to show which suites pass on a clean checkout, and runs prettier to reveal the formatting baseline. Every tool call is permission-gated against allow, ask, and deny rules first.
- how does an AI agent find TypeScript code without the function name
- Atlas searches code with hybrid semantic and keyword retrieval fused by reciprocal rank fusion. codebase_search returns the matching TypeScript declaration even when your wording never appears in the source, because the index is built from AST declarations.
- can I index a private TypeScript codebase locally
- Yes. Atlas can build its code index with local Ollama embeddings, keeping code off third-party servers, so codebase_search still works on a private tsconfig.json project.
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