Atlas plans a multi-file Node.js change in a plan agent whose description is literally Plan mode. Disallows all edit tools. Its permission set denies edit for every path except the plan markdown, so research into your Express routes and npm scripts cannot accidentally turn into an edit to src/server.js. Atlas researches with codebase_search, grep, read, and the lsp tool, all of which stay allowed in plan mode, and writes the design into the one path it can write: an .atlas/plans markdown file. When the plan is ready, plan_exit asks whether to switch to the build agent and start implementing. You approve before a single line of Node.js changes.
How do I plan a change across many Node.js files without editing them?
Switch to the Atlas plan agent. Its permissions deny edit for "*" and allow it only under .atlas/plans/*.md, so a 2026 session designing a change across src/routes, src/middleware, and package.json is structurally incapable of writing to any of them.
A multi-file Node.js change is where agents most often overreach. Adding an auth middleware touches the Express app in src/app.js, every route under src/routes, the npm scripts in package.json, and the node:test suites that assert on the old behavior. Plan mode removes the possibility of a premature edit: the plan agent's description is literally Plan mode. Disallows all edit tools. The design is produced first, reviewed by you, and only then implemented.
What can Atlas actually do in plan mode?
Research with codebase_search, grep, read, and the lsp tool, all of which stay allowed in plan mode. In a Node.js project that means Atlas can read your package.json, trace an Express handler through src/middleware, and enumerate callers, without the ability to change a single file in 2026.
Plan mode is not a reduced agent, it is an agent with writes removed. codebase_search queries the semantic index by meaning, so Atlas can ask where request bodies are validated. grep confirms exact strings such as an npm script name. read pulls the real files. The lsp tool's findReferences enumerates every caller of the function you are about to change. All four are read-only, which is precisely why they remain allowed while edit is denied for "*".
Where does Atlas write the plan for a Node.js change?
Atlas writes the plan into the allowed plan markdown path, which is the one place plan mode can write: under .atlas/plans/*.md. Every other path in your Node.js repository, including src/, package.json, and the node:test files, is denied for the duration of the 2026 planning session.
The plan file is the deliverable. For a Node.js change it should name the real files that will move, the npm scripts that will change, the Express or Fastify routes that will gain middleware, and the node:test suites that must be updated. Because the plan lives in the repository as markdown, it is reviewable in a pull request and durable across sessions. Atlas computes a unified diff for every file edit and surfaces it for approval before writing, so even the plan markdown is shown to you first.
How does Atlas hand off from planning to implementing?
Atlas calls the plan_exit tool, which asks: Plan at <path> is complete. Would you like to switch to the build agent and start implementing? Answering Yes in 2026 hands the Node.js plan off to the build agent, which is the agent that can finally touch src/ and package.json.
The handoff is an explicit gate, not a silent transition. Atlas drafts a plan in a read-only plan agent and asks before switching to a build agent, so no Node.js file is modified on the strength of a plan you have not read. Answering No raises Question.RejectedError and keeps you refining the plan, which is the correct outcome when the design misses a route, forgets a prettier config, or ignores a node:test suite that will break.
What happens if I reject the Atlas plan?
Answering No to plan_exit raises Question.RejectedError and keeps you in plan mode, refining the plan. The Node.js codebase is untouched, because plan mode's permission set still denies edit for "*" and still allows writes only under .atlas/plans/*.md in 2026.
Rejection is a normal move, not an error condition to work around. A first plan for a multi-file Node.js change frequently misses something: a Fastify route registered dynamically, an npm workspace package that also imports the changed module, an integration test that spins up the Express app. Say no, tell Atlas what it missed, and the plan is revised in place. Nothing in src/ has changed, so there is nothing to roll back.
How do I verify a Node.js plan once the build agent implements it?
Verify an implemented Node.js plan by running node:test through npm and reading the unified diff for every file the build agent touched. Atlas snapshots file changes as git patches in 2026, so any edit to src/app.js or package.json can be diffed and rolled back individually.
The plan tells you what should have changed, and the diff tells you what did. Compare them file by file. Run the suite with node:test through your npm script to confirm behavior, and run prettier so the diff carries the change rather than formatting churn. Every Atlas tool call is permission-gated against allow, ask, and deny rules before it runs, so even in build mode you can require approval on writes into src/ while allowing test runs freely.
Step by step
- 01Run atlas where your Node package.json lives, and let Atlas read your modules, npm scripts, and Express or Fastify routes.
- 02Switch to the plan agent; its permissions deny edit for "*" and allow it only under .atlas/plans/*.md.
- 03Research with codebase_search, grep, read, and the lsp tool; all of them stay allowed in plan mode, so Atlas can trace an Express handler through src/middleware without editing it.
- 04Have Atlas enumerate every caller of the function you intend to change with the lsp tool's findReferences operation.
- 05Write the plan into the allowed plan markdown path under .atlas/plans, naming the real Node.js files, the npm scripts, and the node:test suites that will change.
- 06Call plan_exit: it asks Plan at <path> is complete. Would you like to switch to the build agent and start implementing?
- 07Answer Yes to hand off to the build agent; answering No raises Question.RejectedError and keeps you refining the plan.
- 08After the build agent implements, run node:test through npm, run prettier, and review the unified diff for every file it touched.
Frequently asked questions
- how do i make an ai agent plan before editing my node.js code
- Switch Atlas to the plan agent. Its description is literally Plan mode. Disallows all edit tools, and its permission set denies edit for "*" while allowing writes only under .atlas/plans/*.md, so nothing in src/ or package.json can change.
- what tools can atlas use in plan mode
- codebase_search, grep, read, and the lsp tool all stay allowed in plan mode. Atlas can trace an Express handler, enumerate callers with findReferences, and read your npm scripts, but it cannot edit any file outside the plan markdown.
- where does atlas save the plan file
- Under .atlas/plans as a markdown file. That is the one path plan mode is allowed to write, because its permission set denies edit for every other path in your Node.js repository.
- atlas plan_exit prompt what does it do
- plan_exit asks: Plan at <path> is complete. Would you like to switch to the build agent and start implementing? Answering Yes hands off to the build agent, which is the first agent in the session allowed to modify src/ or package.json.
- what happens if i reject an atlas plan
- Answering No raises Question.RejectedError and keeps you in plan mode, refining the plan. Your Node.js code is untouched, so there is nothing to roll back. Tell Atlas what the plan missed and it revises in place.
- how do i verify a multi-file node.js change after the build agent runs
- Run node:test through your npm script, run prettier, and read the unified diff Atlas surfaces for every file it touched. Atlas snapshots file changes as git patches, so any single edit can be diffed and rolled back.
- can atlas plan a change across an express and fastify codebase
- Yes. Run atlas where your Node package.json lives and let it read your modules, npm scripts, and Express or Fastify routes. Plan mode researches all of them with codebase_search and the lsp tool without the ability to edit anything.
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