JSON Formatter and Beautifier

What formatting changes, and what it doesn't

The formatter parses your text into a value and prints it again with consistent whitespace. Strings, numbers, booleans and nulls come out exactly as they went in, and keys keep the order you wrote them in. Two things can look different afterwards, and both come from how JSON is read rather than from the formatter.

First, keys that look like whole numbers, such as "2" or "10", move to the front of their object in numeric order, because that is how JavaScript stores object keys. Second, JSON numbers are read as 64-bit floating point, which is exact only up to 9,007,199,254,740,991. A 20-digit ID such as 12345678901234567890 comes back as 12345678901234567000. If your data has 64-bit IDs, keep them as strings. Escape sequences are also printed in their plain form, so "café" becomes "café", which is the same string.

Choosing an indent

Two spaces is the most common style and what JSON.stringify(value, null, 2) produces. Four spaces is common in Python projects, and tabs let each reader pick their own width. Tick Sort keys to order every object's keys alphabetically at every level. Sorted output is handy before committing fixtures or comparing two API responses, because the same data always prints the same way.

Reading error messages

When the JSON is invalid, the output panel names the problem in plain words and gives its line and column. The line is also highlighted in the input's line-number gutter, and Show in input puts your cursor on the exact character. The messages are the same in every browser because SyntaxSnap uses its own checker to locate the error instead of relying on each browser's wording. A missing comma is usually reported where the next key starts, so look at the end of the line before. For a full list of every problem at once, use the JSON validator.

Fixing almost-JSON

Output from ChatGPT, Claude and other LLMs often arrives inside a markdown code fence with a sentence before it. JavaScript configs use comments, single quotes and unquoted keys, and Python prints True, False and None. Fix common errors handles all of these, adds missing commas, removes trailing ones, closes brackets left open by truncated output, and wraps several concatenated objects in an array. The button only appears when the repaired text is valid JSON. If you just need to read a tsconfig.json or VS Code settings file, tick Allow comments (JSONC) instead and the input is accepted as it is.

Large files

You can open files up to 50 MB. Anything over 1 MB is parsed in a Web Worker, a background thread in the same tab, so the editor keeps responding while it works. The output pane shows the first 400 KB of very large results to keep scrolling smooth; Copy and Download always give you the full text.

Why format JSON locally

API responses often contain access tokens, email addresses and customer records. Many online formatters send what you paste to their server. Here the work happens in your browser tab, and you can check it yourself: open the network tab in your browser's developer tools, then format something. No request is made.