What is envconfig?

envconfig is a Go library that populates your application's configuration from environment variables. Instead of hand-writing code to read each variable and convert it to the right type, you define a struct and let envconfig do the heavy lifting. You write a Go struct listing every setting your app needs, things like a debug toggle, a port number, a timeout duration, or a list of user names. Then you call one function, passing your app's name as a prefix. The library reads the matching environment variables, converts them into the appropriate Go types, and fills in your struct. For example, a string like "3m" becomes a proper Go duration object, and "rob,ken,robert" becomes a slice of three strings. The library gives you control through struct tags. You can mark fields as required so the app fails fast when something is missing, set default values for optional settings, rename fields to match existing variable names, or ignore fields entirely. There's also a split_words option that translates CamelCase field names into snake_case variable names automatically. Beyond built-in types like integers, booleans, floats, strings, slices, and maps, envconfig lets you write custom decoders for complex or unusual data. If you need to parse a specialized format, say, a JSON-encoded list of SMS providers keyed by country, you implement a Decode method on your type and envconfig hands the raw string to your logic. It also respects Go's standard TextUnmarshaler and BinaryUnmarshaler interfaces, so types that already know how to parse themselves work out of the box. This library is aimed at Go developers building applications that run in environments where configuration comes through environment variables, a common pattern for cloud deployments and containerized apps. It saves you from writing repetitive parsing and error-handling code while keeping configuration declarative and easy to scan at the top of your source file.