Module thiserror

Tools for defining custom error types.

• Crate ::thiserror.
• docs.rs
• crates.io
• GitHub

thiserror provides derive macros for creating custom error types that implement std::error::Error with minimal boilerplate.

While anyhow is ideal for applications that need flexible error handling, thiserror is designed for libraries that want to provide specific, well-typed errors that callers can match on and handle precisely.

The Error derive macro automatically implements std::error::Error, Display, and optionally From conversions. It supports error source chaining, custom display messages, and transparent delegation to underlying errors.

Key features include #[error("...")] for custom display messages, #[source] for error source chaining, #[from] for automatic From implementations.

Examples

Define a custom error type with automatic std::error::Error implementation:

#[derive(thiserror::Error, Debug)]
pub enum MyError {
    #[error("failed to parse JSON")]
    Parse(#[from] serde_json::Error),
    #[error("data store disconnected")]
    Disconnect(#[source] std::io::Error),
    #[error("the data for key `{0}` is not available")]
    Redaction(String),
    #[error("invalid header (expected {expected:?}, found {found:?})")]
    InvalidHeader {
        expected: String,
        found: String,
    },
}

fn example() -> Result<(), MyError> {
    Err(MyError::Redaction("secret_key".to_string()))
}