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

Development and Testing with make

This project's makefile (GNUmakefile) is set up to support all of the project's testing, automation and development tasks in a completely deterministic way.

Some make commands are:

• make test
• make lint tidy
• make test-shell
• make test v=1
• make test o='-foo --bar=baz' # Add extra CLI options
• make test GO-VERSION=1.2.34
• make test GO_YAML_PATH=/usr/local/go/bin
• make shell # Start a shell with the local go environment
• make shell GO-VERSION=1.2.34
• make distclean # Remove all generated files including .cache/

Dependency Auto-install

By default, this makefile will not use your system's Go installation, or any other system tools that it needs.

The only things from your system that it relies on are:

• Linux or macOS
• GNU make (3.81+)
• git
• bash
• curl

Everything else, including Go and Go utils, are installed and cached as they are needed by the makefile (under .cache/).

Note: Use make shell to get a subshell with the same environment that the makefile set up for its commands.

Using your own Go

If you want to use your own Go installation and utils, export GO_YAML_PATH to the directory containing the go binary.

Use something like this:

export GO_YAML_PATH=$(dirname "$(command -v go)")
make <rule>
# or:
make <rule> GO_YAML_PATH=$(dirname "$(command -v go)")

Note: GO-VERSION and GO_YAML_PATH are mutually exclusive. When GO_YAML_PATH is set, the Makefile uses your own Go installation and ignores any GO-VERSION setting.

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.

We strongly encourage you to show pertinent output from this command when reporting and discussing issues.

make go-yaml
./go-yaml --help
./go-yaml <<< '
foo: &a1 bar
*a1: baz
' -n        # Show value on decoded Node structs (formatted in YAML)

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.