YAML to JSON converter

YAML and JSON describe the same kinds of data: maps, lists, strings, numbers, booleans and null. YAML adds features that JSON lacks, and the converter has to turn each one into plain data:

Integers larger than 2⁵³ stay exact. Many converters pass them through JavaScript numbers and silently change the last digits of IDs like 12345678901234567890.

YAML 1.2 (2009) cut down the list of values that turn into booleans and numbers. Many tools still follow YAML 1.1, PyYAML among them. Use the version switch above to see what your parser will produce:

The fix is the same in both versions: quote the value ("22:22", "1.10") when you mean text. The YAML validator flags these values in your file.

Command line with yq (v4). Add -I=0 for one compact line per document:

yq -o=json '.' config.yaml > config.json
yq -o=json -I=0 '.' multi-doc.yaml   # one JSON value per line

Python with PyYAML (a YAML 1.1 parser). Use safe_load_all for files with several documents:

import json, yaml

with open("config.yaml", encoding="utf-8") as f:
    data = yaml.safe_load(f)            # or list(yaml.safe_load_all(f))
print(json.dumps(data, indent=2, default=str))  # default=str handles dates

JavaScript / Node.js with the yaml package (YAML 1.2 by default):

import { readFileSync } from 'node:fs';
import { parse, parseAllDocuments } from 'yaml';

const data = parse(readFileSync('config.yaml', 'utf8'));
console.log(JSON.stringify(data, null, 2));

// several documents
const docs = parseAllDocuments(src).map(d => d.toJS());

Go with sigs.k8s.io/yaml, the package Kubernetes tooling uses:

import "sigs.k8s.io/yaml"

j, err := yaml.YAMLToJSON(yamlBytes)

• Duplicate keys. The YAML spec requires unique keys. PyYAML keeps the last value without a word; this tool reports the duplicate so you know which one you lose.
• Custom tags. CloudFormation !Ref, !Sub and !GetAtt are not standard YAML. They are converted as plain values and the tag is dropped, with a warning.
• Tabs. YAML forbids tabs for indentation. If a file came from an editor that inserts tabs, the validator can replace them in one click.
• Going back. To turn the JSON into YAML again, use the JSON to YAML converter. To check or pretty-print the result, use the JSON formatter.

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