effect-best-practices

Use Effect.Service with accessors set to true and declare dependencies in the dependencies array. This gives you automatic accessors, a built-in Default layer, and proper dependency wiring without manual Layer.provide at usage sites.

Define errors with Schema.TaggedError including a message field and relevant context like entity IDs. Handle them with Effect.catchTag or catchTags to preserve type information, and prefer explicit errors like UserNotFoundError over generic NotFoundError.

The Effect Language Server is a TypeScript plugin (@effect/language-service) that detects Effect-specific issues like floating Effects and missing requirements at edit time. Install it as a devDependency and register it in tsconfig.json compilerOptions plugins.

Use Layer.mergeAll for flat composition of same-level layers and Layer.provideMerge for incremental chaining. Deeply nested Layer.provide chains create complex recursive types that slow the TypeScript language server.

Define atoms outside components with Atom.make, add Atom.keepAlive for persistent global state, and render async results with Result.builder using onErrorTag for typed error handling. Use result.waiting for mutation loading state instead of useState.

Running effects synchronously inside services breaks Effect's composition model, loses error handling and tracing, and makes code untestable. Instead, return Effect values from methods using Effect.fn and let the caller compose and run them.