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A StrictYAML implementation for Rust
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A StrictYAML implementation for Rust obtained by savagely chopping off code from yaml-rust.

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This crate was originally started as feature-gated (#[cfg(feature)]) fork of the original.

Making it standalone allows to use both implementations (full and strict) from the same app, with confidence that the documents expected to be StrictYAML compliant will not be parsed as full YAML by mistake.

Mad props going to the original crate author, Chen Yuheng.

What is StrictYAML?

StrictYAML is a subset of the YAML format, removing troublesome parts of the specification:

  • No typing. StrictYAML only knows Strings, Arrays and Dicts (Maps)
  • No duplicate keys
  • No tags
  • No anchors or refs
  • No "flow" style (embedded JSON)

In short, keeping only the parts of YAML that we all know and love.

For more details, see the original documentation and implementation:


Missing from this implementation is a programmatic schema, which would enable document validation and typed value parsing. Seems that you'll still have to parse integers and dates from strings, or send a PR!

Quick Start

Add the following to the Cargo.toml of your project:

strict-yaml-rust = "0.1"


git = ""

and import:

extern crate strict_yaml_rust;

Use yaml::StrictYamlLoader to load the YAML documents and access it as Vec/HashMap:

extern crate strict_yaml_rust;
use strict_yaml_rust::{StrictYamlLoader, StrictYamlEmitter};

fn main() {
    let s =
    - list1
    - list2
    - 1
    - 2.0
    let docs = StrictYamlLoader::load_from_str(s).unwrap();

    // Multi document support, doc is a yaml::Yaml
    let doc = &docs[0];

    // Debug support
    println!("{:?}", doc);

    // Index access for map & array
    assert_eq!(doc["foo"][0].as_str().unwrap(), "list1");
    assert_eq!(doc["bar"][1].as_str().unwrap(), "2.0");

    // Chained key/array access is checked and won't panic,
    // return BadValue if they are not exist.

    // Dump the YAML object
    let mut out_str = String::new();
        let mut emitter = StrictYamlEmitter::new(&mut out_str);
        emitter.dump(doc).unwrap(); // dump the YAML object to a String
    println!("{}", out_str);

Note that strict_yaml_rust::StrictYaml implements Index<&'a str> AND Index<usize>:

  • Index<usize> assumes the container is an Array
  • Index<&'a str> assumes the container is a string to value Map
  • otherwise, Yaml::BadValue is returned


  • Pure Rust
  • Ruby-like Array/Hash access API
  • Low-level StrictYAML events emission

Specification Compliance

This implementation aims to provide StrictYAML parser fully compatible with the StrictYAML specification.


Licensed under either of

at your option.


Fork & PR on Github.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

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