Introduction

omnimod is a modular, plugin-based codemod tool for TypeScript / JavaScript / React codebases. A small core provides the codemod machinery; plugins encapsulate specific transformations.

Why omnimod

• Formatting-preserving. The core parses with oxc-parser (ESTree AST, UTF-16 offsets) and applies edits as magic-string splices, so untouched code stays byte-identical. Generated files are then run through the target project's own formatter, so output matches its conventions.
• Modular. The engine knows nothing about any specific transformation. A plugin is one object with a transform function (plus optional analyze and finalize for cross-file work).
• Batteries included. Seven plugins ship today — styling (styled-to-vanilla-extract), dates (moment-to-dayjs), testing (jest-to-vitest), utilities (lodash-to-es-toolkit), state (redux-to-toolkit), React (react-class-to-hooks) and build tooling (webpack-to-vite).

Packages

Package	Responsibility
@omnimod/core	Parse, walk, the Plugin contract, run() orchestration, diffs, formatting.
@omnimod/plugin-utils	Helpers for plugin authors (shared ESTree node types + cast, CSS-in-JS parsing, a vanilla-extract object model, import management).
@omnimod/cli	The omnimod command.
@omnimod/plugin-*	Plugins.

How it works

run(plugin, options) does the orchestration:

1. Discover — glob the project (respecting .gitignore) for files matching the plugin's include.
2. Parse each file once into an AST + a magic-string edit buffer.
3. analyze — an optional first pass over every file that collects cross-file facts into a shared ProjectContext.state.
4. transform — the main pass: each file is rewritten via its edit buffer, and new files can be emitted.
5. finalize — an optional last pass that emits shared files (e.g. a theme contract, or a migration report).
6. Write / dry-run — with write: true, changed and emitted files are written and formatted; otherwise a colored diff is returned.

Next: Getting started.