JSON to YAML Converter

How JSON maps to YAML

Every JSON type has a direct YAML form:

• An object becomes a mapping: one key: value per line, with nested objects indented under their key.
• An array becomes a list with one - item per line. An array of objects puts the first key on the dash line, like - name: web.
• Strings lose their quotes unless YAML would read them as something else. Values that start with a character YAML treats specially (#, &, *, !, @, ? or - ), contain : , end in :, or are empty get single quotes.
• Numbers, true, false and null keep their type. Numbers are printed the way JavaScript prints them, so 59.90 becomes 59.9 and 1e3 becomes 1000. Empty arrays and objects stay inline as [] and {}.
• A string with line breaks becomes a literal block (| or |-), which keeps every line break. A string with a tab or a carriage return gets double quotes with \t or \r escapes instead.

Why some values get quotes

Many YAML parsers still follow YAML 1.1, which turns more plain words into booleans, numbers and dates than YAML 1.2 does. PyYAML and the Go library behind kubectl are two of them. Here's what PyYAML 6 reads when these values aren't quoted:

• yes, no, on and off, in their usual capitalizations, become booleans. This is the "Norway problem": the list [GB, NO, SE] loads as ['GB', False, 'SE']. The YAML 1.1 spec also lists y and n, so the converter quotes those as well.
• 01234 becomes 668, because YAML 1.1 reads a leading zero as octal. A YAML 1.2 parser reads 1234. Either way, a postal code loses its zero.
• 1.10 becomes the float 1.1, which breaks version numbers.
• 22:22 becomes 1342, because YAML 1.1 reads base-60 numbers. That's why Docker's Compose docs ask for port mappings as quoted strings.
• 2024-01-15 becomes a date object, not a string.
• A value that starts with * is read as an alias, so an unquoted cron schedule like */15 * * * * is a parse error. The Cron Expression Generator explains what such a schedule means.

When to keep JSON and when to switch

Keep JSON for data that programs send to each other. It's strict, every language reads it the same way, and there's no indentation to get wrong. Switch to YAML for files that people write and review, where comments and fewer quotes matter more than strictness.

You don't always have to convert. YAML 1.2 treats JSON as valid YAML, and kubectl apply -f accepts a .json manifest directly. Convert when a team will edit the file, when you want to add comments, or when a tool only documents YAML examples.

Convert JSON to YAML in code

PyYAML sorts keys unless you pass sort_keys=False, and it doesn't indent list items under their key. Both styles are valid YAML.

import json, yaml

with open("config.json") as f:
    print(yaml.safe_dump(json.load(f), sort_keys=False))

const fs = require("fs");
const yaml = require("js-yaml");

const data = JSON.parse(fs.readFileSync("config.json", "utf8"));
console.log(yaml.dump(data, { lineWidth: -1 }));

yq -p json -o yaml config.json > config.yaml

import "sigs.k8s.io/yaml"

y, err := yaml.JSONToYAML(jsonBytes)

require "json"
require "yaml"

puts JSON.parse(File.read("config.json")).to_yaml