JSON vs YAML vs XML: which format should you use?

By Uxair Ijaz · 2026-10-22 · 2 min read

JSON, YAML and XML can all describe the same data. Here is one small record in each:

{ "name": "Ada", "languages": ["en", "fr"], "active": true }

name: Ada
languages:
  - en
  - fr
active: true

<person active="true">
  <name>Ada</name>
  <languages><language>en</language><language>fr</language></languages>
</person>

JSON: the default for APIs

Strengths: tiny grammar, native to JavaScript, supported by every language, fast to parse. Weaknesses: no comments, strict about commas and quotes, no dates (they travel as strings).

The errors people hit most often:

• A trailing comma after the last item: [1, 2, 3,].
• Single quotes instead of double quotes around strings or keys.
• Unquoted keys, which JavaScript allows but JSON does not.
• Comments, which JSON does not support at all.

The JSON validator points to the exact line and column of each of these, with a hint on how to fix it.

YAML: configuration humans edit

Strengths: readable, supports comments, great for config files (Kubernetes, GitHub Actions, Docker Compose). Weaknesses: whitespace matters, and some values change type by surprise:

• no, off and yes can become booleans in older YAML parsers (the "Norway problem": the country code NO turning into false).
• 1.10 becomes the number 1.1. Quote version numbers.
• Tabs are not allowed for indentation.

YAML is a superset of JSON, so any JSON file is also valid YAML. Convert with JSON to YAML, or tidy a file with the YAML formatter.

XML: documents and older systems

Strengths: attributes and mixed content, schemas (XSD) for strict validation, namespaces, mature tooling. It is still everywhere in banking, government, SOAP services, Office files and RSS. Weaknesses: verbose, and there is no single obvious way to map it to objects (attribute or element? one item or a list?).

To work with XML in a JSON world, use XML to JSON; to read it, the XML formatter.

Which should I choose?

• Data between programs, especially web APIs → JSON.
• Config files people edit by hand → YAML, or JSON with comments if your tools allow it.
• Documents, strict schemas, or a system that already speaks it → XML.

The data format converter moves data between all three, plus CSV.