Converting YAML to JSON (and Back)

YAML is a superset of JSON

Since YAML 1.2, every valid JSON document is also valid YAML — a YAML parser will read JSON unchanged. That's because both share the same core data model: mappings (objects), sequences (arrays), and scalars (strings, numbers, booleans, null). Converting YAML data to JSON is therefore just a matter of parsing the YAML into that shared model and re-serializing it as JSON.

# YAML                          // JSON
server:                         {
  host: localhost                 "server": {
  port: 8080                        "host": "localhost",
roles:                              "port": 8080
  - admin                         },
  - editor                        "roles": ["admin", "editor"]
                                }

What doesn't survive the conversion

The conversion is lossless for data but lossy for everything YAML offers beyond data. When you convert YAML to JSON, you lose:

• Comments. JSON has no comment syntax, so every # line is dropped. This is the most common surprise when converting config files.
• Anchors and aliases. &defaults / *defaults let YAML reuse a block; JSON has no references, so the converter inlines a full copy wherever the alias appeared. Data is preserved, the sharing is not.
• Multiple documents. A YAML file can hold several documents separated by --- (common in Kubernetes manifests). JSON has no multi-document concept, so these are typically emitted as a JSON array, one element per document.
• Custom tags and non-string keys. YAML allows tags like !!python/object and complex (non-string) mapping keys; JSON keys must be strings, so these don't translate.

The type-inference gotcha carries over

Because YAML infers types before JSON ever enters the picture, a value already became a boolean or number during the YAML parse. So code: NO in YAML converts to "code": false in JSON, and zip: 01234 may become "zip": 668 (octal) or 1234. If the JSON output looks wrong, the cause is almost always an unquoted YAML value — quote it at the source.

Converting in code

In Python:

import yaml, json
data = yaml.safe_load(open("config.yaml"))
print(json.dumps(data, indent=2))

In JavaScript with js-yaml:

import yaml from "js-yaml";
const data = yaml.load(yamlString);
const json = JSON.stringify(data, null, 2);

Going the other way — JSON to YAML — is yaml.dump(json.load(...)) in Python or yaml.dump(JSON.parse(...)) in JS. Since JSON has no comments or anchors to begin with, JSON→YAML is fully lossless.

Convert YAML to JSON now

Paste YAML and get clean, formatted JSON instantly — or convert to XML. Runs in your browser, nothing uploaded.

Frequently Asked Questions