SWE Agents are Better with Codemods

Coding assistants like Cursor have brought us into a new era of programming.
But there’s a class of programming tasks that remain outside their reach: large-scale, systematic modifications across large codebases. You wouldn’t ask an AI to delete all your dead code or reorganize your entire component hierarchy—the tooling just isn’t there.

That’s where codemods come in.

A codemod is a program that operates on a codebase, and when you give an AI agent the ability to write and execute them, these platform-level tasks fall below the high-water mark of AI capabilities.

Here’s a real example:
We asked Devin (an autonomous SWE agent) to “delete all dead code” from our codebase. Instead of making hundreds of individual edits, Devin wrote and debugged a program that systematically removed unused code while handling edge cases like tests, decorators, and indirect references.

• View the PR
• View on Devin

What made this work?

Devin operates like a state machine: write a codemod → run it through the linter → analyze failures → refine.

Each iteration adds handling for new edge cases until the codemod successfully transforms the codebase.

This mirrors the same cycle developers use for large-scale refactors—just automated.

The best part? You don’t have to blindly trust the AI.

The codemod is a program you can review, run, and verify with linter and test output. You can edit it to add exceptions or improve coverage—much better than reviewing hundreds of individual diffs.

Try it yourself

Want to try this with your own Devin instance?

Install the Codegen CLI:

uv tool install codegen --python 3.13

Then use this prompt:
Download Dead Code Deletion Prompt

Supported Codemods with Codegen

• Convert Promises to async/await:
  Automatically convert Promise chains to async/await syntax across your codebase.
• Organize Codebase:
  Move and reorganize code safely with automatic import and dependency handling.
• Modernize React:
  Convert class components to hooks, standardize props, and organize components.
• Migrate Tests to Pytest:
  Convert unittest test suites to modern pytest style.

We’d love to hear how it works for you.
Join our community and share your experience developing codemods with Devin or other code assistants.