go.yaml.in/yaml

YAML Support for the Go Language

Introduction

The yaml package enables Go programs to comfortably encode and decode YAML values.

It was originally developed within Canonical as part of the juju project, and is based on a pure Go port of the well-known libyaml C library to parse and generate YAML data quickly and reliably.

Project Status

This project started as a fork of the extremely popular go-yaml project, and is being maintained by the official YAML organization.

The YAML team took over ongoing maintenance and development of the project after discussion with go-yaml's author, @niemeyer, following his decision to label the project repository as "unmaintained" in April 2025.

We have put together a team of dedicated maintainers including representatives of go-yaml's most important downstream projects.

We will strive to earn the trust of the various go-yaml forks to switch back to this repository as their upstream.

Please contact us if you would like to contribute or be involved.

Version Intentions

Versions v1, v2, and v3 will remain as frozen legacy. They will receive security-fixes only so that existing consumers keep working without breaking changes.

All ongoing work, including new features and routine bug-fixes, will happen in v4. If you’re starting a new project or upgrading an existing one, please use the go.yaml.in/yaml/v4 import path.

Compatibility

The yaml package supports most of YAML 1.2, but preserves some behavior from 1.1 for backwards compatibility.

Specifically, v3 of the yaml package:

• Supports YAML 1.1 bools (yes/no, on/off) as long as they are being decoded into a typed bool value. Otherwise they behave as a string. Booleans in YAML 1.2 are true/false only.
• Supports octals encoded and decoded as 0777 per YAML 1.1, rather than 0o777 as specified in YAML 1.2, because most parsers still use the old format. Octals in the 0o777 format are supported though, so new files work.
• Does not support base-60 floats. These are gone from YAML 1.2, and were actually never supported by this package as it's clearly a poor choice.

Installation and Usage

The import path for the package is go.yaml.in/yaml/v4.

To install it, run:

go get go.yaml.in/yaml/v4

API Documentation

See: https://pkg.go.dev/go.yaml.in/yaml/v4

API Stability

The package API for yaml v3 will remain stable as described in gopkg.in.

Example

package main

import (
	"fmt"
	"log"

	"go.yaml.in/yaml/v4"
)

var data = `
a: Easy!
b:
  c: 2
  d: [3, 4]
`

// Note: struct fields must be public in order for unmarshal to
// correctly populate the data.
type T struct {
	A string
	B struct {
		RenamedC int   `yaml:"c"`
		D	[]int `yaml:",flow"`
	}
}

func main() {
	t := T{}

	err := yaml.Unmarshal([]byte(data), &t)
	if err != nil {
		log.Fatalf("error: %v", err)
	}
	fmt.Printf("--- t:\n%v\n\n", t)

	d, err := yaml.Marshal(&t)
	if err != nil {
		log.Fatalf("error: %v", err)
	}
	fmt.Printf("--- t dump:\n%s\n\n", string(d))

	m := make(map[any]any)

	err = yaml.Unmarshal([]byte(data), &m)
	if err != nil {
		log.Fatalf("error: %v", err)
	}
	fmt.Printf("--- m:\n%v\n\n", m)

	d, err = yaml.Marshal(&m)
	if err != nil {
		log.Fatalf("error: %v", err)
	}
	fmt.Printf("--- m dump:\n%s\n\n", string(d))
}

This example will generate the following output:

--- t:
{Easy! {2 [3 4]}}

--- t dump:
a: Easy!
b:
  c: 2
  d: [3, 4]


--- m:
map[a:Easy! b:map[c:2 d:[3 4]]]

--- m dump:
a: Easy!
b:
  c: 2
  d:
  - 3
  - 4

Testing with make

Running make test in this directory should just work. You don't need to have go installed and even if you do the GNUmakefile will ignore it and setup / cache its own version under .cache/.

The only things you need are:

• Linux or macOS
• git
• bash
• curl
• make

Some make commands are:

• make test
• make test GO-VERSION=1.2.34
• make shell Start a shell with the local go environment
• make shell GO-VERSION=1.2.34
• make distclean - Removes .cache/

The go-yaml CLI Tool

This repository includes a go-yaml CLI tool which can be used to understand the internal stages and final results of YAML processing with the go-yaml library.

make go-yaml
./go-yaml --help
./go-yaml -t <<< '
foo: &a1 bar
*a1: baz
'

You can also install it with:

go install go.yaml.in/yaml/v4/cmd/go-yaml@latest

License

The yaml package is licensed under the MIT and Apache License 2.0 licenses. Please see the LICENSE file for details.