Pretty-Print

Pretty-print is the act of re-formatting a serialised document so a human can read it comfortably. For JSON, pretty-printing inserts newlines after commas and braces, indents nested structures with a consistent number of spaces or tabs, and puts each key-value pair on its own line.

A before-and-after

Before (compact):

{"user":{"id":42,"roles":["admin","editor"]},"active":true}

After (pretty-printed, 2-space indent):

{
  "user": {
    "id": 42,
    "roles": ["admin", "editor"]
  },
  "active": true
}

The data is the same; any parser produces the same in-memory structure from either form. Pretty-printing is a surface change only.

Why it exists

Serialised data is optimised for machines: compact, unambiguous, easy to transmit. Humans who need to read the data in a debugger, a log viewer, or an incident postmortem want visual structure. Pretty-printing adds that structure without touching the meaning.

Cost and benefit

Pretty-printing makes documents roughly 25-35% bigger in raw bytes. After HTTP compression (gzip, brotli), the penalty shrinks to under 10% for most payloads. For transmission-heavy workloads the compact form wins slightly; for debugging and development, pretty form wins overwhelmingly.

The usual compromise: pretty on disk, minified on the wire, pretty again when displayed. Conversion in either direction is cheap.

Pretty-print in different contexts

• JSON: indent each level; put each object member on its own line; arrays may fit on one line if short.
• XML: insert a newline before each child element; indent nested elements; preserve whitespace inside <pre>-like elements.
• HTML: similar to XML but tolerates inline elements (<em>, <strong>) staying on the same line as their parent’s text.
• CSS: one rule per line; one declaration per line; aligned property: value.
• SQL: one clause per line; keywords aligned; parameters indented.

Tooling

• JavaScript: JSON.stringify(obj, null, 2) for JSON. prettier handles JavaScript, JSON, CSS, HTML, and more.
• Python: json.dumps(obj, indent=2).
• Go: json.MarshalIndent.
• Command line: jq . is the canonical JSON pretty-printer.
• Online: the JSON tool on this site does it in your browser, with indent options and sort-keys.

For a deeper discussion of when to pretty vs. minify, see the guide Pretty-print vs. minify.