JSON formatter and validator

Pretty-printed, minified, sorted: what changes and what does not

Outside of strings, JSON ignores spaces, tabs and line breaks. A formatter only adds or removes that whitespace, so the data you get back is the same data: the same keys, the same values, the same order of items in every array. What changes is who it is easy to read for.

• 2 or 4 spaces for reading, code reviews and config files. Two spaces keep deep nesting from drifting off the right edge; four make each level easier to tell apart.
• Tabs when your project indents with tabs, or when you want each reader's editor to choose the width.
• Minify for sending: one line, no spaces between tokens. Indentation costs bytes on every line, so minified JSON is what belongs in request bodies, environment variables and single-line fields.

Sort keys reorders the keys inside every object, at every depth, including objects inside arrays. The JSON standard treats an object's keys as unordered, so nothing a program reads changes. It pays off before comparing two versions of a response: once both are sorted and indented the same way, Compare text in Text Studio shows only the real differences, line by line.

Why JSON fails to validate

The formatter parses your text before it prints it, so it is a validator too. It follows the JSON standard strictly, exactly as a browser's JSON.parse does. These are the mistakes that trip it most often:

• A comma after the last item, as in [1, 2, 3,]. JavaScript code allows it; JSON does not.
• Single quotes around keys or strings. JSON wants double quotes, and every key must be quoted.
• Comments. // and /* */ are not JSON. Files such as VS Code's settings.json and tsconfig.json use a looser dialect, often called JSONC, that allows them.
• Curly quotes like “ and ” that crept in through a word processor or a chat app. They look right and are not.
• Values JSON cannot express: undefined, NaN, Infinity, or a date written as new Date(...).
• A raw line break or tab inside a string. It has to be written as \n or \t.

The note under the panes starts with "Not valid JSON:" and goes on with the parser's own explanation, which usually names the character it did not expect and where it is. Fix that spot and the result appears at once.

What can change when JSON is reformatted

Formatting is safe for almost everything, but a parser turns the text into values and then writes those values back out. Four details do not survive that round trip exactly as typed:

• Very long integers. 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. Data with IDs like that should keep them as strings.
• How numbers are spelled. 1.0 comes out as 1, and 1e3 as 1000. The values are equal; the text is not.
• Repeated keys. If an object has the same key twice, the last one wins and the first disappears without a warning.
• Escapes. \u00e9 is written back as é, and \/ as /. Both mean the same thing to any JSON reader.

None of this matters for configs and ordinary API responses. It matters when you paste in a database export full of 64-bit IDs and paste the result straight back.

Formatting JSON that should stay private

JSON is what APIs answer with, so the JSON people paste into formatters is often a live response: a user record with an email and a home address, an order with a payment reference, a config file with an API key or a database password in it. Plenty of web formatters do their work in the browser. Others offer to save your JSON or make a link to share it, which means keeping it on a server. From the page alone, it is hard to tell which kind you are on.

The Dev Toolbox has no server to send anything to. The formatter runs inside the Octoolo app on your computer, works with the network unplugged, and forgets the text when you move to another tool. Its neighbors work the same way: JSON to CSV for turning an array into a table, the JWT decoder for tokens found in a response, and Base64 for the encoded fields inside it.