Convert YAML to JSON: Command Line, Python, and JavaScript

YAML and JSON represent the same data structures — objects, arrays, strings, numbers, booleans, null — just with different syntax. YAML is meant for humans to write; JSON is meant for machines to parse. Converting between them is straightforward once you understand the mapping.

YAML vs JSON: same structure, different syntax

# YAML
name: John Doe
age: 30
active: true
tags:
  - developer
  - writer
address:
  city: New York
  zip: "10001"

{
  "name": "John Doe",
  "age": 30,
  "active": true,
  "tags": ["developer", "writer"],
  "address": {
    "city": "New York",
    "zip": "10001"
  }
}

Same data. YAML uses indentation and colons; JSON uses braces, brackets, and commas.

Python: PyYAML + json

pip install pyyaml

import yaml
import json

# YAML string → JSON string
yaml_text = """
name: John Doe
age: 30
active: true
tags:
  - developer
  - writer
"""

data = yaml.safe_load(yaml_text)
json_text = json.dumps(data, indent=2)
print(json_text)

From a file:

import yaml, json

with open("config.yaml", "r") as f:
    data = yaml.safe_load(f)

with open("config.json", "w") as f:
    json.dump(data, f, indent=2)

Always use yaml.safe_load() instead of yaml.load(). The load() function can execute arbitrary Python code embedded in YAML — a serious security risk if the YAML comes from an untrusted source.

Python: JSON to YAML

import yaml, json

with open("config.json", "r") as f:
    data = json.load(f)

with open("config.yaml", "w") as f:
    yaml.dump(data, f, default_flow_style=False, allow_unicode=True)

default_flow_style=False forces block style (indented) rather than inline {key: value} style.

JavaScript / Node.js: js-yaml

npm install js-yaml

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

// YAML file → JSON string
const yamlText = fs.readFileSync('config.yaml', 'utf8');
const data = yaml.load(yamlText);
const jsonText = JSON.stringify(data, null, 2);
fs.writeFileSync('config.json', jsonText);

JSON to YAML:

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

const data = JSON.parse(fs.readFileSync('config.json', 'utf8'));
const yamlText = yaml.dump(data);
fs.writeFileSync('config.yaml', yamlText);

Command line (no code)

yq is a YAML/JSON command-line processor (like jq but for YAML):

# Install
brew install yq          # macOS
snap install yq          # Linux

# YAML → JSON
yq -o=json config.yaml

# JSON → YAML
yq -o=yaml config.json

# Write to file
yq -o=json config.yaml > config.json

Python one-liner (no install needed beyond Python itself):

python3 -c "import sys, yaml, json; print(json.dumps(yaml.safe_load(sys.stdin), indent=2))" < config.yaml

Things that don't convert cleanly

A few YAML features have no direct JSON equivalent:

• Comments — # this is a comment — dropped entirely in the conversion.
• Multi-document YAML — a file with multiple --- separators — you'd need to handle each document separately.
• Custom types (!!python/object) — safe_load rejects these; they have no JSON mapping.
• Anchors and aliases (&anchor / *alias) — these are expanded by the YAML parser before JSON serialization, so you lose the deduplication but the data is preserved.
• Non-string keys — YAML allows keys like 123 or true; JSON requires string keys. Most parsers stringify them, but it's worth knowing.