env-required

Ultra-lightweight required environment variable validation for Rust.

Zero dependencies (std-only)
One macro: required!
Helpful panic messages (designed for backend/CLI/server startup)
Optional FromStr parsing

If you want your program to fail fast with a clear message when configuration is missing, this crate is for you.

Installation

[dependencies]
env-required = "0.1"

Quick Start (single env)

use env_required::required;

fn main() {
    let database_url = required!("DATABASE_URL");
    println!("db={database_url}");
}

Validate Many (startup check)

use env_required::required;

fn main() {
    required!(["DATABASE_URL", "PORT", "RUST_LOG"]);

    // ...start your app
}

Type Conversion (`FromStr`)

use env_required::required;

fn main() {
    let port: u16 = required!("PORT" => u16);
    let workers: usize = required!("WORKERS" => _); // `_` lets the compiler infer the type.

    println!("port={port} workers={workers}");
}

Custom Message

use env_required::required;

fn main() {
    let token = required!("API_TOKEN", "API_TOKEN is required to call Example API");
    required!(["DATABASE_URL", "PORT"], "missing configuration for my-service");
    println!("token_len={}", token.len());
}

Why a macro?

required! is a macro because:

It gives a single, memorable entry point without importing multiple helpers.
We can provide syntax-level guidance (and compile_error! for misuses).
It keeps call sites short and consistent in binaries and libraries.

Internally, the macro expands to small std::env helpers. There is no hidden magic.

FAQ

Why panic instead of returning `Result`?

This crate targets startup configuration validation.

If required configuration is missing, continuing is usually incorrect and leads to harder-to-debug failures later. Fail-fast panics produce a single, clear error early.

If you need a Result-based API (e.g. for a long-running library), consider implementing a thin wrapper around this macro, or see the "Alternative API" idea in the crate documentation.

Does it load `.env` files?

No.

This crate intentionally does not include a .env loader to stay dependency-free. If you want .env support, use a loader in your binary (e.g. dotenvy) and then call required!.

Is an empty string considered missing?

By default, yes (KEY="" is treated as missing).

Enable feature allow-empty to treat empty strings as present:

[dependencies]
env-required = { version = "0.1", features = ["allow-empty"] }

MSRV

Rust 1.56 (Edition 2021).

License

MIT OR Apache-2.0

env-required 0.1.0