Configuration

Cloud-native applications are configured from the outside: ports, hostnames, feature flags, and secrets all arrive through environment variables, .env files, or mounted config volumes. Effect models configuration declaratively. You describe what you need with a Config, and a ConfigProvider decides where the raw values come from. The result is configuration that is typed, validated, and trivially mockable in tests.

There are three pieces to understand:

Config<T> — a recipe for extracting and validating a value of type T. A Config is itself an Effect, so you yield* it inside Effect.gen.
ConfigProvider — the backing data source. The default reads from environment variables, but you can swap in JSON, a .env file, or an in-memory map.
Redacted — a wrapper for secrets that keeps sensitive values out of logs and error output.

import { Config, Effect } from "effect"

const program = Effect.gen(function* () {
  // Each Config reads and validates one value from the current ConfigProvider
  const host = yield* Config.string("HOST")
  const port = yield* Config.port("PORT") // validated integer in 1–65535
  yield* Effect.log(`Listening on ${host}:${port}`)
})

// With no provider specified, Config reads from process.env by default:
//   HOST=localhost PORT=8080 node app.js
Effect.runFork(program)

Because a Config resolves the current ConfigProvider from context, the same program runs unchanged against environment variables in production and a fixed map in tests — you only swap the provider.

In this section

Config

Build and combine Config values, supply defaults, and validate inputs. Read more

Config Providers

Control where configuration is read from — env vars, JSON, .env files, or your own source. Read more

Redacted Secrets

Handle API keys and passwords safely with Redacted. Read more