effect

name	effect
description	Work with Effect v4 / effect-smol TypeScript code. Use when writing, reviewing, or refactoring TypeScript code using the Effect library (Effect.gen, Context.Tag, Layer, Schema, Effect.fn).

Effect

This codebase uses Effect for typed, composable TypeScript services, schemas, and workflows.

Source Of Truth

Use the current Effect v4 / effect-smol source, not memory or older Effect v2/v3 examples.

1. If .opencode/references/effect-smol is missing, clone https://github.com/Effect-TS/effect-smol there. Do this in the project, not in the skill folder.
2. Search .opencode/references/effect-smol for exact APIs, examples, tests, and naming patterns before answering or implementing Effect-specific code.
3. Also inspect existing repo code for local house style before introducing new patterns.
4. Prefer answers and implementations backed by specific source files or nearby repo examples.

Guidelines

• Prefer current Effect v4 APIs and project-local patterns over old blog posts, examples, or package-memory guesses.
• Use Effect.gen(function* () { ... }) for multi-step workflows.
• Use Effect.fn("Name") or Effect.fnUntraced(...) for named effects when adding reusable service methods or important workflows.
• Prefer Effect Schema for API and domain data shapes. Use branded schemas for IDs and Schema.TaggedErrorClass for typed domain errors when modeling new error surfaces.
• Keep HTTP handlers thin: decode input, read request context, call services, and map transport errors. Put business rules in services.
• In Effect service code, prefer Effect-aware platform abstractions and dependencies over ad hoc promises where the surrounding code already does so.
• Keep layer composition explicit. Avoid broad hidden provisioning that makes missing dependencies hard to see.
• In tests, prefer the repo's existing Effect test helpers and live tests for filesystem, git, child process, locks, or timing behavior.
• Do not introduce any, non-null assertions, unchecked casts, or older Effect APIs just to satisfy types.
• Do not answer from memory. Verify against .opencode/references/effect-smol or nearby code first.

Testing Patterns

• Use testEffect(...) from packages/opencode/test/lib/effect.ts for tests that exercise Effect services, layers, runtime context, scoped resources, or platform integrations.
• Use it.live(...) for filesystem, git repositories, HTTP servers, sockets, child processes, locks, real time, and other live platform behavior.
• Run tests from package directories such as packages/opencode; never run package tests from the repo root.
• Prefer explicit test layers over ad hoc managed runtimes. Keep dependency provisioning visible in the test file.
• Use scoped fixtures and finalizers for resources that must be cleaned up, including temporary directories, flags, databases, fibers, servers, and global state.