How to Minify JSON (and When It Actually Helps)

{
  "id": 42,
  "name": "Asha",
  "tags": [
    "admin",
    "beta"
  ]
}

{"id":42,"name":"Asha","tags":["admin","beta"]}

Only whitespace between tokens is removed. Whitespace inside string values is part of the data, so a correct minifier leaves it alone. Keys, values and their order are unchanged.

In a browser tool

Paste your JSON into an editor and run its Minify command. A tool that validates first will tell you if the input is not valid JSON, instead of producing broken output.

In JavaScript

const minified = JSON.stringify(JSON.parse(text)); // no third argument means no extra whitespace

In Python

import json

data = json.loads(text)
minified = json.dumps(data, separators=(",", ":"), ensure_ascii=False)

On the command line

jq -c . data.json > data.min.json

It depends on how deeply the data is indented and how much of it is whitespace. As a test, we generated a list of 50 orders (each with a customer and two line items) and measured it in four forms:

The practical conclusion is to turn on HTTP compression first, because it benefits every response, and to minify as well when the text is not compressed, for example JSON embedded in an HTML page, written to a cache or stored in a size-limited field.

• API responses and request bodies, where bandwidth and latency matter. Most frameworks already write compact JSON by default.
• JSON embedded in web pages or sent to browsers inside scripts.
• Values stored in caches, queues or database fields with size limits or per-byte costs.
• Static data files shipped with an application.

• Configuration files in version control. Minified JSON is one long line, so every change shows as the whole file changing, and people cannot review it.
• Files people read or edit by hand, and log lines meant to be read by humans. Keep the formatted version and minify only in the build or on the wire.
• Data you plan to compare line by line. Format and sort it first so that diffs are meaningful.

A good habit is to keep the readable version as the source of truth and generate the minified one automatically as part of a build step.

• It is not encryption or obfuscation. Anyone can format minified JSON again with one click.
• It does not fix invalid JSON. A comment or trailing comma is still an error afterwards, and a good tool will refuse to minify it.
• It does not reduce what is inside the data. For larger savings, send fewer fields, paginate large lists, or consider a binary format such as MessagePack or Protocol Buffers when you control both ends.
• It does not preserve exactness of huge numbers if the tool parses them as floats. Check identifiers longer than 15 digits after any parse-and-rewrite step.