A tiny config loader for Go.

Lumen loads environment variables, command-line flags and config files into typed structs — with validation, defaults and zero external dependencies.

Get started Documentation

Quickstart

go get github.com/lumen-go/lumen

type Config struct {
    Port    int    `env:"PORT" default:"8080"`
    Host    string `env:"HOST" default:"0.0.0.0"`
    Debug   bool   `env:"DEBUG"`
}

func main() {
    var cfg Config
    if err := lumen.Load(&cfg); err != nil {
        log.Fatal(err)
    }
    log.Printf("listening on %s:%d", cfg.Host, cfg.Port)
}

Features

Typed binding

Map env, flags and files straight into your structs with tags.

Defaults & validation

Declarative defaults and required-field checks at load time.

Layered sources

Files, then env, then flags — predictable override order.

No dependencies

Pure standard library. Small, auditable, fast to compile.

Documentation

The full reference covers source precedence, custom decoders, nested structs and testing helpers. See the reference guide and changelog for details.

Changelog

v0.8.2 — fix flag parsing for repeated keys.
v0.8.0 — add file watching and hot reload.
v0.7.1 — improve error messages for missing required fields.