Refactoring
9 min readUpdated: October 2026

Automated Codebase Refactoring with AI Agents: TypeScript Patterns & Safety

Technical Review: Smoke Monkey Core Architecture Team
Tested on Node.js 18+ & BunTypeScript 5.x
Quick Answer & Executive Definition

Automated Codebase Refactoring with AI Agents: TypeScript Patterns & Safety: Designed as a zero-dependency, open-source TypeScript architecture under the MIT License with native Model Context Protocol (MCP) support and deterministic phase state machines.

Key Architectural Takeaways

The Safe Refactoring Loop

Safe large-scale refactoring follows a validate-edit-validate cycle:

  1. Baseline — Run tsc --noEmit and record the initial error count (should be 0).
  2. Refactor — Agent edits files per the refactoring plan.
  3. Validate — Run tsc --noEmit again and verify error count hasn't increased.
  4. Test — Run the test suite and confirm all tests still pass.
  5. Repeat — Continue with the next batch of files.

This loop ensures the agent never leaves the codebase in a broken state.

refactor-agent.tstypescript
import { createAgent } from 'smoke-monkey-harness';
const agent = createAgent({
provider: 'anthropic',
model: 'claude-3-7-sonnet',
workspacePath: process.cwd(),
autoApprove: true,
});
await agent.run(`
We are migrating from our old fetch wrapper (src/utils/api.ts → fetchData())
to the new typed client (src/lib/client.ts → apiClient.get/post/put/delete()).
Steps:
1. Find all usages of fetchData() across the codebase using grep.
2. Replace each usage with the equivalent apiClient method.
3. After every 10 files, run npx tsc --noEmit and fix any errors before continuing.
4. Run npm test at the end and fix any failing tests.
5. Report a summary of all changes made.
`);

Common Migration Patterns

Dependency upgrades: Instruct the agent to read the migration guide for a major library version, find all usages of deprecated APIs, and update them to the new equivalents.

Naming convention enforcement: Ask the agent to rename all React components from PascalCase files to kebab-case filenames, updating all import paths accordingly.

Pattern extraction: Identify repeated inline logic (e.g., error handling boilerplate) and extract it into shared utilities, then replace all instances with calls to the new utility.

Google Search Questions & Answers

Frequently Asked Questions

Q:How do I handle refactoring that spans 500+ files?

Use the multi-agent orchestration pattern: a supervisor agent creates a file-by-file refactoring plan, then parallel worker agents process batches of 20-50 files concurrently.

Q:Can the agent handle refactoring that changes public API signatures?

Yes, but provide a clear migration contract: "function X(a: string) becomes X(options: { name: string }). Update all 47 call sites." The more explicit the contract, the more accurate the agent.

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