# Migrating a Large Flow Monorepo to TypeScript

DevFeed: [Migrating a Large Flow Monorepo to TypeScript](<https://devfeed.tech/articles/migrating-a-large-flow-monorepo-to-typescript-27431.md>)

Original publisher: [Read original article](<https://engineeringblog.yelp.com/2026/08/migrating-a-large-flow-monorepo-to-typescript.html>)

Author: Shawn Walton, Software Engineer

Published: 2026-08-04T00:00:00Z

Content type: article

Language: en

Sources: [Yelp](<https://devfeed.tech/sources/yelp.md>)

Topics: [monorepo](<https://devfeed.tech/topics/monorepo.md>), [TypeScript](<https://devfeed.tech/topics/typescript.md>), [migration](<https://devfeed.tech/topics/migration.md>), [repo](<https://devfeed.tech/topics/repo.md>), [Code](<https://devfeed.tech/topics/code.md>)

Tags: [coverage](<https://devfeed.tech/tags/coverage.md>), [integrity](<https://devfeed.tech/tags/integrity.md>), [migration](<https://devfeed.tech/tags/migration.md>), [monorepo](<https://devfeed.tech/tags/monorepo.md>), [open-source](<https://devfeed.tech/tags/open-source.md>), [rewrite](<https://devfeed.tech/tags/rewrite.md>), [typescript](<https://devfeed.tech/tags/typescript.md>)

## AI overview

Yelp describes its gradual migration of a large Flow monorepo to TypeScript. The team chose a package-by-package approach to preserve type-checking trust and type safety while Flow and TypeScript coexisted in production, using open-source conversion tooling, custom codemods, and manual fixes.

## Source excerpt

In early 2017, Webcore selected Flow as Yelp's next-generation typechecker over TypeScript. At the time there was no clear frontrunner. Flow had better support for React, better performance, and a respectable repository of types for NPM packages in flow-typed. However, a few years later the landscape had shifted, and it became clear that TypeScript was emerging as the stronger choice. TypeScript's DefinitelyTyped repo had thousands more packages than flow-typed, and many more packages shipped with built-in TypeScript headers. TypeScript also proved to be more stable over time, and limited uptake in the wider JS community made finding tools and documentation...