Config & Schema

When to use

• Validating request bodies, params, or external inputs

• Loading environment configuration with types

Config (example)

import { Config } from "effect"

const Server = Config.nested("SERVER")(Config.all({ host: Config.string("HOST"), port: Config.number("PORT") }))

Schema Validate

import { Schema as S } from "effect"

const User = S.Struct({ id: S.Number, name: S.String }) const decodeUser = (u: unknown) => S.decodeUnknown(User)(u)

Transform

const IsoDate = S.String // then transform to Date in pipeline where needed

Real-world snippet: Layer selecting AWS credentials via Config options

class AwsCredentials extends Effect.Service<AwsCredentials>()("AwsCredentials", { effect: Effect.gen(function* () { const accessKeys = yield* Config.option( Config.all([Config.string("CAP_AWS_ACCESS_KEY"), Config.string("CAP_AWS_SECRET_KEY")]) ) const vercelAwsRole = yield* Config.option(Config.string("VERCEL_AWS_ROLE_ARN"))

const credentials = yield* Effect.gen(function* () {
  if (Option.isSome(vercelAwsRole)) return awsCredentialsProvider({ roleArn: vercelAwsRole.value })
  if (Option.isSome(accessKeys)) {
    const [accessKeyId, secretAccessKey] = accessKeys.value
    return { accessKeyId, secretAccessKey }
  }
  return fromContainerMetadata()
})

return { credentials }

}) })

Guidance

• Prefer schemas close to boundaries; keep core logic typed

• For branded types (Email, PositiveInt), use transform/brand helpers

• Validate early, map to domain errors in one place

Pitfalls

• Accepting unknown into core → always decode first

• Large ad-hoc validation code → centralize in Schema

Cross-links

• HTTP & Routing for endpoint validation

• Foundations for operator style

Local Source Reference

CRITICAL: Search local Effect source before implementing

The full Effect source code is available at docs/effect-source/ . Always search the actual implementation before writing Effect code.

Key Source Files

• Config: docs/effect-source/effect/src/Config.ts

• Schema: docs/effect-source/schema/src/Schema.ts

Example Searches

Find Config patterns and options

grep -F "Config.string" docs/effect-source/effect/src/Config.ts grep -F "Config.number" docs/effect-source/effect/src/Config.ts grep -F "Config.option" docs/effect-source/effect/src/Config.ts

Study Schema validation

grep -F "Struct" docs/effect-source/schema/src/Schema.ts grep -F "decodeUnknown" docs/effect-source/schema/src/Schema.ts

Find Schema transforms

grep -rF "transform" docs/effect-source/schema/src/ grep -rF "brand" docs/effect-source/schema/src/

Look at Config test examples

grep -F "Config." docs/effect-source/effect/test/Config.test.ts

Workflow

• Identify the Config or Schema API you need

• Search docs/effect-source/effect/src/Config.ts or docs/effect-source/schema/src/Schema.ts

• Study the types and validation patterns

• Look at test files for usage examples

• Write your code based on real implementations

Real source code > documentation > assumptions

References

• Agent Skills overview: https://www.anthropic.com/news/skills

• Skills guide: https://docs.claude.com/en/docs/claude-code/skills