Effect Program Design

Build production Effect v4 programs with small domain-shaped interfaces, typed success and error channels, declared dependencies, observable operation boundaries, and tests that substitute layers at real seams. This skill combines broad Effect mechanics with deep-module, capture-before-narrow, and real-seam design standards.

Source rule

Check these before guessing:

1. the nearest CLAUDE.md / AGENTS.md and project-local conventions;
2. the installed effect, @effect/*, and related package versions and declarations;
3. the Effect v4 docs at https://effect-ts-effect-smol.mintlify.app/;
4. the pinned/upstream source (~/projects/effect-smol) when docs do not settle an API.

effect/unstable/* can change between beta/minor versions. Typecheck examples against the installed version. Local project conventions take precedence unless the task explicitly changes them.

References