JSON vs XML: How the Two Formats Compare

Why does the same book record take 156 characters in XML but only 114 in JSON? Both formats carry the same facts, yet they wrap them in very different ways. XML names every piece twice, with an opening and a closing tag. JSON uses braces, brackets and quoted keys, and that choice changes far more than file size.

What Sets JSON and XML Apart?

JSON is a small data format built from objects and arrays. XML is a markup language built from tagged elements. Both are plain text, both nest data, and both can describe the same record.

JSON is defined twice, by IETF RFC 8259 and by the Ecma standard ECMA-404. Both editions date from December 2017. The Ecma page calls JSON a lightweight, text-based and language-independent syntax, derived from the ECMAScript programming language.

XML comes from the W3C, and its core rules sit in XML 1.0, now in its Fifth Edition. XML was built for documents as well as data. That is why it keeps features JSON lacks, such as attributes, comments and text mixed with tags.

XML is also strict about structure. Every start tag needs a matching end tag, and attribute names cannot repeat inside one tag. Our guide to HTML to XML converters and well-formed markup shows how those rules catch loose HTML.

Reading the Two Syntaxes

JSON has six kinds of values. RFC 8259 lists four simple types, strings, numbers, booleans and null, plus two structured types, objects and arrays. An object is an unordered set of name and value pairs, and an array is an ordered list.

XML has one main building block, the element. An element is a start tag, some content and an end tag, like <year>2024</year>. Extra facts can ride inside the start tag as attributes, like id="42".

Notice the types row. In JSON, 2024 and "2024" are different values. In plain XML, both are just the text 2024.

One Book Record, Written Both Ways

Take a small book record with an ID, a title, a year, a price, a stock flag and two authors. Here it is in both formats, side by side.

With the extra spaces removed, the XML is 156 characters and the JSON is 114. The JSON is about 27 percent shorter, mostly because it skips closing tags. The JSON also carries real types: 42 and 2024 are numbers, and true is a boolean.

What the Converter Returns

Paste the XML version into our converter, and it returns this JSON:

{"book": {"@id": "42", "title": "Clean Data", "year": "2024", "price": "19.99", "inStock": "true", "author": ["Ana Ruiz", "Ben Cole"]}}

Three details stand out. The attribute became a key with an @ sign, the two authors became an array, and every value stayed a quoted string. That is correct behavior, since the XML itself never said 2024 was a number.

How Do Attributes, Arrays, Comments and Schemas Differ?

XML has two places for data, attributes and child elements, while JSON has only keys. XML shows lists by repeating an element, JSON uses arrays, and only XML allows comments.

Attributes vs Keys

An XML attribute sits inside the start tag and holds one text value. The W3C rules say attribute order inside a tag does not matter, and a name cannot appear twice. JSON has no such split, so converters mark attributes with a prefix such as @.

Arrays vs Repeated Elements

XML has no list marker at all. Two author elements in a row simply mean two authors. JSON makes the list explicit with square brackets, and RFC 8259 defines an array as an ordered sequence.

Comments

XML allows comments almost anywhere outside other markup, written as <!-- note -->. The JSON grammar in RFC 8259 has no comment syntax at all. Teams that need notes in JSON often add a plain key, such as “note”, instead.

Schemas: XSD vs JSON Schema

A schema is a rulebook that says which fields exist and what type each holds. XML uses XSD, a W3C Recommendation whose version 1.1 dates from April 2012. JSON uses JSON Schema, whose current version is 2020-12, split into Core and Validation documents.

Where XML to JSON Conversion Slips

Most conversion trouble comes from features one format has and the other lacks. These six cases show up in our converter and in most other XML to JSON tools.

• Numbers arrive as strings. XML has no number type, so “2024” and “true” stay text. Change them to real numbers and booleans before math or sorting.
• Leading zeros matter. A ZIP code such as 02134 is safest as a string. Turned into a number, it becomes 2134.
• One item is not an array. A single author comes out as a plain string, while two come out as an array. Code that expects a list breaks on the one-author record.
• Attributes on text-only elements vanish. In our converter, an element that holds only text keeps the text and drops its attributes. The currency in the price row above is lost this way.
• Comments and mixed text disappear. JSON has no place for comments. Loose text beside child tags, such as “Hello” in <p>Hello <b>world</b></p>, is also dropped.
• Very large IDs lose precision. RFC 8259 notes that software agrees exactly on integers up to 9,007,199,254,740,991, which is 2 to the 53rd power minus 1. Keep longer IDs as strings.

Which Format Fits Your Project?

Pick JSON for web APIs, settings files and simple records with typed values. Pick XML when you need attributes, comments, mixed text in documents, or an existing XSD rulebook.

Many systems use both. An older service might send XML while a newer web app expects JSON. In that case, convert at the edge and then check the six trouble spots above once.

Moving the other way needs care too, since JSON arrays and null values have no single XML form. For that direction, use the JSON to XML converter. To try your own records, paste them into the free XML to JSON converter and read the output line by line.

Common Questions About JSON and XML

References

This article is general education on data formats. Converter examples reflect how the XML to JSON Converter behaves as of this update. Reviewed for accuracy by Prof. Dr. Khalil Mudassar, PhD. Last updated September 27, 2026.