JSON vs XML vs YAML: Which Data Format Should You Use?

What does the same data look like in each format?

Here is one small record, a user with a name, two tags and an active flag, in each format. In JSON it is {"name": "Ali", "tags": ["a", "b"], "active": true}. The JSON Formatter prints it with two-space indentation, one key per line.

In YAML the same record is three lines: name: Ali, then tags: followed by two list items written as - a and - b, then active: true. In XML it might be <user active="true"><name>Ali</name><tags><tag>a</tag><tag>b</tag></tags></user>. XML has no built-in list or boolean type, so the author decides whether active is an attribute or an element and how tags are wrapped.

How do JSON, XML and YAML compare?

The table summarises the main differences. JSON is defined in RFC 8259, YAML in the YAML 1.2.2 specification and XML in the W3C XML 1.0 recommendation.

When is JSON the best choice?

JSON suits data sent between programs. Its grammar is small: objects, arrays, strings in double quotes, numbers, true, false and null. RFC 8259 also says JSON exchanged between systems that are not part of a closed ecosystem must be encoded in UTF-8, which removes a whole class of character-set problems.

The strictness is a feature. There are no comments, no trailing commas and no single-quoted strings, so any two parsers should read the same text the same way. JavaScript can turn JSON into objects with JSON.parse, and most languages ship a JSON library.

When is YAML the better choice?

YAML is popular for configuration because people can read and edit it with little punctuation and leave comments that explain each setting. Lists, nested maps and long strings are easy to write.

The cost is that whitespace matters. A wrong indent changes the structure or makes the file invalid, and tabs are not allowed for indentation. Unquoted values can also be interpreted in ways you did not intend, so quote strings that look like numbers, dates or booleans, such as version numbers or country codes.

When should I still use XML?

XML remains the right choice when a standard requires it, for example many document formats, RSS feeds, SOAP services and industry data exchanges. It supports attributes, namespaces and mixed content, where text and tags are interleaved, which JSON and YAML handle awkwardly.

XML also has mature schema languages and transformation tools. If you need strict validation of a document's shape and the systems you talk to already speak XML, switching to JSON may add more work than it saves.

Can I convert between the formats?

JSON to YAML is the easiest conversion, because YAML 1.2 aims to be a superset of JSON. JSON to XML and back needs decisions about attributes, repeated elements and types, so automated converters can produce different results.

Whichever direction you go, validate the result. For JSON, paste it into the JSON Formatter and click Validate. For tabular data, the CSV to JSON and JSON to CSV tools convert between rows and objects.

What mistakes are common in each format?

In JSON, the usual problems are trailing commas, single quotes, unquoted keys and comments left in from JavaScript or a config template. Each one makes the whole document fail to parse, so a validator catches them immediately.

In YAML, the usual problems are inconsistent indentation, a tab character where spaces were expected, and unquoted values that a parser reads as a different type, such as a version number like 1.10 being treated as a number. Quoting values that must stay strings avoids most surprises.

In XML, the usual problems are a missing closing tag, tags closed in the wrong order, an unescaped ampersand or less-than sign in text, and attribute values without quotes. XML parsers stop at the first well-formedness error, much as JSON parsers do.

Are there safety differences between the formats?

Any format can be risky if a program trusts input blindly. With JSON, the main rule is to parse with a real JSON parser such as JSON.parse rather than evaluating the text as code. With YAML and XML, some libraries support features that load custom objects or external entities, so use safe-loading options and keep libraries up to date.

Whatever the format, validate the structure and values your application expects after parsing. A syntactically valid file can still contain a wrong type, a missing field or an unexpectedly large value.

What tools help with each format?

For JSON, a formatter and validator is the first stop: paste the text, check it, then pretty-print it for reading or minify it for sending. Code editors also highlight JSON errors as you type.

For YAML, many editors and CI systems offer linting that flags indentation and duplicate keys. For XML, schema validators check a document against an XSD or similar definition. Using the checker that matches the format, before the file reaches production, prevents most failures.

How do I choose a format for a project?

1. Check what the other side expects. If an API, platform or standard specifies a format, use it.
2. Consider who edits the file. Hand-edited configuration favours YAML; machine-generated data favours JSON.
3. Think about validation. Need schemas and namespaces? XML has the most mature tools. JSON Schema covers many JSON cases.
4. Validate before shipping. Run JSON through the JSON Formatter so syntax errors are caught early.

Example

What should I keep in mind?

FAQ

Is YAML a superset of JSON?

YAML 1.2 was designed so that JSON documents are valid YAML, which is why many YAML parsers can read JSON files.

Is JSON faster to parse than XML?

Usually, because its grammar is simpler and many runtimes have built-in parsers, but speed depends on the library and the data.

Can JSON have comments?

No. RFC 8259 does not allow comments, so a parser such as JSON.parse rejects them.

Why do so many config files use YAML?

Because it is easy to read, allows comments and needs fewer brackets and quotes than JSON or XML.

Does XML have data types?

Not by itself. Everything is text unless a schema defines types for elements and attributes.

Which format is smallest?

For the same data, minified JSON and YAML are usually much smaller than XML because XML repeats each tag name when closing it.

Can YAML use tabs for indentation?

No. YAML indentation must use spaces.

Is JSON5 the same as JSON?

No. JSON5 adds features such as comments and trailing commas; standard JSON parsers reject those.

Should I store dates as strings in JSON?

Yes. JSON has no date type, so ISO 8601 strings such as 2026-11-04 are the common choice.

How do I check JSON before converting it to YAML?

Paste it into the JSON Formatter and click Validate. Fix any error it reports, then convert.

When is XML still the better choice?

Choose XML for document-centric data, mixed content, or ecosystems that already standardize on schemas and namespaces.

Why do APIs prefer JSON over YAML?

JSON parses unambiguously in browsers and has broad first-class support; YAML’s indentation is better for humans editing configs.

Can XML attributes replace nested elements?

Attributes suit simple scalars; nested elements fit repeated or complex structures—style guides differ by schema.

How do I migrate a YAML config to JSON?

Parse YAML with a trusted library, then serialize JSON—watch duplicate keys and unquoted special values.

Is binary JSON (BSON) interchangeable with JSON?

No—BSON adds types and is not plain text JSON; convert explicitly when crossing systems.

Do XML namespaces work in JSON?

JSON has no native namespaces; encode them as property naming conventions if you must map across.

Why is YAML sensitive to whitespace errors?

Indentation defines structure; a one-space slip can nest keys incorrectly without a loud syntax error.

Can I validate YAML with a JSON Schema?

Some toolchains allow it after conversion; native YAML schema efforts exist but JSON Schema is more common.

Which format supports streaming large payloads best?

JSON and XML both have streaming parsers; YAML is usually loaded as a whole document.

Should I pretty-print JSON in git repos?

Pretty-printed JSON improves diffs; minify only for wire transfer if size matters.

Sources and further reading

• RFC 8259 – The JSON Data Interchange Format
• YAML Ain't Markup Language version 1.2.2