What is anyhow?

anyhow is a Rust crate by David Tolnay(2019) that gives application code one error type — anyhow::Error. You return anyhow::Result<T> and use ? to bubble errors up to main without writing a custom error enum for every failure.

Why anyhow: Different steps can fail with different error types (reqwest::Error, std::io::Error, …). anyhow converts them all into one type. anyhow::Context::context(...) adds a short message so you know where it failed.

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    let response = anyhow::Context::context(
        reqwest::get("https://example.com").await,
        "HTTP request failed",
    )?;
    let body = anyhow::Context::context(
        response.text().await,
        "reading response body failed",
    )?;

    println!("{body}");
    Ok(())
}

If something fails, you see a chain like: reading response body failed → HTTP request failed → ...

If we don't use anyhow, what do we lag behind on?

Custom error enums everywhere — you must define enum AppError and add From for every library error type yourself.
No easy context chain — without .context(), errors only say “connection reset” with no hint that it happened during “fetch user config”.
Box<dyn Error> boilerplate — works for propagation, but no context, downcast, or backtrace helpers out of the box.
Mixed error types in main — hard to combine I/O, HTTP, JSON, and DB errors in one return type without anyhow or a large hand-written enum.
Slower debugging — more time tracing failures because messages don't stack up step by step.

Scopes for anyhow

Compare with other crates

docs.rs/anyhow