JSON to YAML Converter

How the two formats relate

YAML 1.2 is a strict superset of JSON: every valid JSON document is already valid YAML, which is why you can paste JSON into the YAML side of this tool and it works. The reverse is not true.

So: JSON → YAML is always safe. YAML → JSON is safe only if the YAML avoids the features in that list. This tool flags each one it finds.

The YAML traps worth knowing

The Norway problem

Under YAML 1.1 — which PyYAML and several other widely-used parsers still implement — these bare words are booleans:

countries:
  - NO      # false under YAML 1.1
  - SE      # the string "SE"
enabled: on   # true under YAML 1.1, the string "on" under 1.2

YAML 1.2 core, used by this tool, treats them all as strings. Since you often cannot control which parser reads your file, quote anything that could be misread: "NO", "on".

Version numbers become numbers

version: 1.10    # the number 1.1, not the string "1.10"
version: "1.10"  # correct

The trailing zero is lost because 1.10 parses as a float. Always quote version numbers.

Colons inside values

title: Release: v2      # error — YAML sees a nested key
title: "Release: v2"   # correct

Tabs are illegal

YAML forbids tabs for indentation outright. Since editors often insert them invisibly, this is a common cause of a file that looks correct and will not parse.

Converting on the command line

# yq — the usual choice
yq -P '.' file.json          # JSON to YAML
yq -o=json '.' file.yaml     # YAML to JSON

# Python, with PyYAML installed
python -c 'import json,sys,yaml; print(yaml.safe_dump(json.load(sys.stdin), sort_keys=False))' < file.json
python -c 'import json,sys,yaml; print(json.dumps(yaml.safe_load(sys.stdin), indent=2))' < file.yaml

Note sort_keys=False — PyYAML sorts keys alphabetically by default, which makes the diff on a config file useless. This tool preserves key order for the same reason.