JSON vs XML vs YAML: Differences and When to Use Each

What each format is

JSON (JavaScript Object Notation) stores data as objects (key and value pairs), arrays, strings, numbers, booleans and null. It is the default format for web APIs and many data files.

XML (Extensible Markup Language) describes data with nested, named tags that can also carry attributes. It is common in document formats, feeds, enterprise systems and older web services.

YAML uses indentation instead of brackets or tags. It reads closely to plain notes and is widely used for configuration files, such as those for build and deployment tools.

The same data in three formats

Here is one small record written three ways. All three describe the same person.

JSON

{
  "name": "Amina",
  "age": 30,
  "languages": ["English", "Urdu"],
  "active": true
}

XML

<person>
  <name>Amina</name>
  <age>30</age>
  <languages>
    <language>English</language>
    <language>Urdu</language>
  </languages>
  <active>true</active>
</person>

YAML

name: Amina
age: 30
languages:
  - English
  - Urdu
active: true

Notice a difference that matters: JSON and YAML know that 30 is a number and true is a boolean. In plain XML every value is text, and the meaning of 30 comes from a schema or from the program reading it.

Comparison table

Strengths and weaknesses

JSON is simple, strict and supported almost everywhere. Its weaknesses are no comments, no trailing commas and no native date type, which is usually stored as a string.

XML handles documents, mixed content and metadata through attributes, and it has mature validation and transformation tooling. It is verbose, and namespaces add complexity.

YAML is pleasant to write and supports comments, but its flexibility brings surprises. Indentation errors change meaning, and parsers may guess types.

Common pitfalls

• YAML indentation. Use spaces, not tabs, and keep nesting consistent. One misplaced space can change the structure.
• YAML implicit typing. Unquoted values can be read as something else. Depending on the parser version, no, yes or on may become booleans, and 1.0 may become a number. Quote values when the text must stay text.
• XML verbosity and namespaces. Repeating tag names inflate files, and namespace prefixes confuse newcomers.
• JSON strictness. A trailing comma or single-quoted string makes the file invalid.
• Assuming equivalent parsers. Different libraries handle edge cases differently, especially with YAML.

How to choose

1. Building or consuming an API: JSON.
2. A person will edit the file often and wants comments: YAML.
3. Document-like data, mixed text and markup, or a partner requiring XML: XML.
4. You need strong, standardised validation of structure: XML with a schema, or JSON with JSON Schema.
5. Tabular rows for a spreadsheet: CSV rather than any of these.

Converting between formats

Converting is easy mechanically but not always lossless. Before you convert, consider what the target format cannot represent:

• JSON to YAML: comments are not an issue because JSON has none, and the data maps closely. Strings that look like numbers or booleans may need quotes in the output.
• JSON to XML: objects become elements, but XML needs a single root and valid tag names. Attributes need a convention.
• Anything to JSON: comments and XML attributes have no place to go and are dropped or encoded in a custom way.
• CSV and JSON: CSV is flat, so nested JSON has to be flattened and may not return to the same shape.

The converters on this site run in your browser. Start with the JSON formatter to check that your JSON is valid, then use JSON to XML or JSON to YAML. For spreadsheet data, try JSON to CSV and CSV to JSON.

Common mistakes when converting

• Converting without checking the source is valid first.
• Expecting comments to survive a trip through JSON.
• Forgetting that XML values are text unless a schema says otherwise.
• Using deeply nested JSON and expecting a neat flat CSV.
• Not reviewing the result before it goes into production.

For a related topic, see how Base64 lets binary data travel inside any of these text formats in the Base64 guide.