How to Handle Unknown Fields in Serde

Add the #[serde(default)] attribute to your struct to ignore unknown fields during deserialization, or use #[serde(deny_unknown_fields)] to explicitly reject them. By default, Serde ignores unknown fields unless deny_unknown_fields is set.

use serde::Deserialize;

#[derive(Deserialize)]
#[serde(default)]
struct Config {
    name: String,
    // Unknown fields in JSON will be ignored
}

Alternatively, to fail on unknown fields:

use serde::Deserialize;

#[derive(Deserialize)]
#[serde(deny_unknown_fields)]
struct Config {
    name: String,
}

Serde decides what to do with extra data in your JSON by default. If you don't tell it otherwise, it simply ignores any fields it doesn't recognize, letting your program run smoothly. If you want strict validation, you can flip a switch to make it crash if it sees anything unexpected.