# Refactor Legacy Code Safely

## Modernize your codebase  without breaking production

Record live traffic, refactor with confidence, verify identical behavior. Turn months of manual test writing into days of safe modernization.

## Refactor legacy code faster with peace of mind

### Before
Traditional Approach

• Write tests manually: 3-6 months

• Put off refactoring until code freezes

• Coverage based on developers' gut

• Miss edge cases that happen in prod

• Hope nothing breaks

### After
With Tusk Drift

• Record live traffic: 1 week

• Refactor whenever convenient

• Coverage from actual user behavior

• Capture real edge cases automatically

• Know nothing broke

## Record real-world traffic before refactoring

Run Tusk Drift in staging or production at 1-10% sampling rate for a week to capture actual API behavior: HTTP requests, database queries, cache hits, and more

## Code fearlessly with a safety net in place

Migrate from Express to Fastify, break up monoliths, and re-organize code with the security that your changes are checked for backwards compatibility

## Verify that nothing breaks in your PR

Replay recorded traces against refactored code to ensure API behavior remains the same –– all tests green means you're good to merge

## Stop being paralyzed by legacy code

[Try free today ](https://app.usetusk.ai/app)

### Helpful resources on AI automated testing

[Does Real API Traffic Make AI-Generated Tests Better? An A/B Evaluation of Tusk Drift](/content/resources/real-api-traffic-ai-generated-tests-evaluation/index.html)

March 9, 2026

[Scaling Parallel Agents with the Context-Verification-Harness Framework](/content/resources/scaling-parallel-coding-agents-cvh-framework/index.html)

March 8, 2026

[What if Your Production Traffic Was Your Test Suite?](/content/resources/what-if-your-production-traffic-was-your-test-suite/index.html)

February 11, 2026

[How Promptfoo Scaled Test Coverage Without Slowing Development](/content/resources/how-promptfoo-scaled-test-coverage-with-tusk/index.html)

February 2, 2026