---
title: "Write a struct to a YAML file in Rust"
url: https://recursiveai.org/oneyaml/rust/cookbook/write-yaml/
description: "Write a Rust struct to a YAML file with serde and oneyaml::to_string: derive Serialize, skip empty fields, and read the file back. A complete program with its real output."
version: "1.2.0"
---

# Write a struct to a YAML file in Rust

Derive serde’s `Serialize` and call `oneyaml::to_string`. Fields come out in declaration order, in block style.

```shell
cargo new write-yaml && cd write-yaml
cargo add oneyaml@1.2.0 serde -F serde/derive
```

Put this in `src/main.rs` and run `cargo run`:

```rust
use serde::{Deserialize, Serialize};
use std::collections::BTreeMap;

#[derive(Debug, Serialize, Deserialize, PartialEq)]
#[serde(rename_all = "camelCase")]
struct Service {
    name: String,
    image: String,
    replica_count: u32,
    ports: Vec<u16>,
    env: BTreeMap<String, String>,
    #[serde(skip_serializing_if = "Option::is_none")]
    healthcheck: Option<String>,
    note: String,
}

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let svc = Service {
        name: "web".into(),
        image: "nginx:1.27".into(),
        replica_count: 2,
        ports: vec![80, 443],
        env: BTreeMap::from([("LOG_LEVEL".into(), "info".into())]),
        healthcheck: None,
        note: "no".into(),
    };

    let yaml = oneyaml::to_string(&svc)?;
    std::fs::write("service.yaml", &yaml)?;
    print!("{yaml}");

    // Read it back: the same value.
    let back: Service = oneyaml::from_str(&std::fs::read_to_string("service.yaml")?)?;
    println!("round trip equal: {}", back == svc);
    Ok(())
}
```

```text
name: web
image: nginx:1.27
replicaCount: 2
ports:
  - 80
  - 443
env:
  LOG_LEVEL: info
note: 'no'
round trip equal: true
```

`healthcheck` is `None` and `skip_serializing_if` leaves it out; without it, it’s written as `null`. `to_writer` writes to any `io::Write`, and `to_string_with` takes `SerializeSettings`.

## Limits

- **No comments.** A struct has nowhere to keep them, so the output has none. To change a file people maintain by hand and keep its comments, edit it as a `Document`: [edit YAML and keep its comments](https://recursiveai.org/oneyaml/rust/cookbook/edit-yaml-keep-comments/).
- **Strings stay strings for every reader.** A string that another reader could take for a different type is quoted: `note` is written `'no'`, so YAML 1.1 tools don’t read it as `false` ([the Norway problem](https://recursiveai.org/oneyaml/articles/yaml-norway-problem/)).

To read the file into the struct: [parse YAML into a struct](https://recursiveai.org/oneyaml/rust/cookbook/parse-yaml-into-structs/).