Effect-TS

Effect is a TypeScript library for building production-grade software with typed errors, structured concurrency, dependency injection, and built-in observability.

Version Detection

Before writing Effect code, detect which version the user is on:

# Check installed version
cat package.json | grep '"effect"'

• v3.x (stable, most production codebases): Context.Tag, Effect.catchAll, Effect.fork, Data.TaggedError
• v4.x (beta, Feb 2026+): ServiceMap.Service, Effect.catch, Effect.forkChild, Schema.TaggedErrorClass

If the version is unclear, ask the user. Default to v3 patterns for existing codebases, v4 for new projects.

Primary Documentation Sources