Changing a function signature and manually updating its 40 call sites is exactly the kind of work Composer removes from your day. Here's how to use it well.
Cursor's chat answers questions and suggests changes you apply file by file. Composer (accessible with Cmd/Ctrl + I) operates in agent mode: it takes a goal, decides which files it needs to read and modify, generates a plan of changes across the whole repository, and presents a consolidated diff before applying anything. The key difference is that Composer can create new files, delete code in multiple locations, and run terminal commands (if you grant permission) as part of the same flow.
A real case: renaming a user_id field to account_id across the codebase because the data model changed from "users" to multi-user "accounts."
Composer identifies the relevant files using the repo index, shows what it's going to touch before writing, and respects explicit exclusions like the audit table one. That explicit exclusion matters: without it, it's common for the model to over-generalize and touch something it shouldn't.
Composer shows a list of files it's going to modify before touching anything, with a per-file summary of intent. Never blindly accept the full plan on a large refactor; check at least:
- Whether it touches config or .env files that shouldn't change. - Whether the count of affected files matches what you expected (if you expected 6 and it touches 20, something over-generalized). - Whether it includes migration files with duplicate names or conflicting timestamps, a common problem in Laravel/Rails when two developers generate migrations the same day.
Every Composer application is left as a point you can revert independently of git history, useful when a refactor goes wrong halfway through. Even so, the recommended practice is to work on a clean branch and commit before invoking Composer on large changes — that way you have git reversion as a real fallback, not just Cursor's internal history.
For refactors that cross layers (backend and frontend at once), be explicit about which files to include in the context using @ to reference specific files or folders, instead of trusting automatic indexing to find everything. This is especially important in monorepos with multiple packages, where the index may prioritize the wrong package.
Composer shines at mechanical, coordinated refactors, but it's not the right tool for ambiguous design decisions ("should we use Redis or Postgres for this queue?"). There, it's better to use regular chat to discuss options first, and reserve Composer for execution once the decision is made. Mixing design exploration with execution in the same prompt produces inconsistent plans because the model tries to decide and execute at the same time.
Treat Composer's output as the first draft of a pull request, not the final result. Run linters, tests, and a full git diff before pushing. In teams with CI, it's good practice to require that any PR with changes mostly generated by Composer include in its description what prompt was used, so the reviewer understands the original intent of the change and can evaluate whether the result matches it.
Carlos Montiel is an enterprise AI solutions architect. He implements LLMs, Agents, RAG, and orchestrators for companies across Guatemala and Latin America. Reach out for a consultation.
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