JSON Tools

JSON Formatter & Validator

Format, beautify, and validate JSON instantly in a professional VS Code-style editor — free, fast, and 100% private.

In short

A JSON formatter re-indents a JSON document so its nesting is readable and, because it must fully parse the text first, reports the exact line and column of the first syntax error. This one runs entirely in your browser, formats as you type, offers 2-, 3-, 4-space, tab or minified output, sorts keys, repairs common mistakes and filters with JMESPath.

By NaveenKumar T · Updated 18 Sep 2026

Learn: What is JSON? A Practical Introduction

Formats as you type
Exact error line & column
2 / 3 / 4-space, tab, or minified

Runs entirely in your browser — nothing you paste or open here is uploaded, logged, or stored.How we handle data →

Example

JSON Formatter: input and output

A minified support ticket from a helpdesk API — the kind of single-line payload you'd copy straight out of browser dev tools.

Input · json

{"ticket_id":"TCK-48213","subject":"Login fails on iOS app after update","status":"open","priority":"high","assignee":"grace.hopper@nv-toolkit.dev","tags":["auth","mobile","regression"],"created_at":"2026-08-14T09:12:00Z","comments":3,"customer":{"name":"Priya Nair","plan":"pro"}}

Output · json

{
  "ticket_id": "TCK-48213",
  "subject": "Login fails on iOS app after update",
  "status": "open",
  "priority": "high",
  "assignee": "grace.hopper@nv-toolkit.dev",
  "tags": [
    "auth",
    "mobile",
    "regression"
  ],
  "created_at": "2026-08-14T09:12:00Z",
  "comments": 3,
  "customer": {
    "name": "Priya Nair",
    "plan": "pro"
  }
}

The formatter re-indents every nested level — including the tags array and the nested customer object — at 2 spaces without changing a single value.

Why this tool

Built for developers who live in JSON

A fast, private and beautifully simple workspace. No sign-up, no server round-trips — your data never leaves the browser.

Instant beautify

Format messy JSON with 2, 3, 4-space or tab indentation, with line numbers and full syntax highlighting.

Pinpoint validation

Strict RFC 8259 validation that highlights the exact line where your JSON breaks — no guessing.

Collapsible tree

Explore deeply nested structures in an interactive tree view — fold branches and read keys at a glance.

One-click convert

Transform JSON into XML, CSV or YAML, or escape it as a string — copy or download the result in a tap.

Private by design

Everything runs client-side. We never upload, store or transmit your data to any server.

Live stats

See line count, byte size, node count and nesting depth update in real time as you work.

Learn more

What is a JSON formatter?

A JSON formatter takes raw JSON — often a dense, single-line API response — and rewrites it with consistent indentation and line breaks so its structure becomes readable. JSON (JavaScript Object Notation) is the default data format of the modern web, but it is designed for machines first: a server has no reason to add whitespace, so the payloads developers actually work with are frequently impossible to scan by eye.

This formatter performs a complete parse of your document before printing it, which means it is also a strict validator. Anything that violates the JSON specification — a trailing comma, a single-quoted string, an unquoted key — is caught and reported with the exact line and column, instead of being silently mangled.

How to format JSON online

Paste your JSON into the input pane on the left. The tool formats it instantly and continuously — there is no submit step, although the Format button is there when you want it. Choose your indentation (2 spaces, 4 spaces, tabs, or minified) and optionally enable 'Sort keys' to order every object's properties alphabetically, which makes large documents easier to diff and review.

When the output looks right, use Copy to put it on your clipboard or Download to save it as a .json file. Clear resets the workspace, and Sample loads a realistic example document if you just want to explore how the tool behaves.

Common JSON syntax errors and how to fix them

The most frequent JSON mistakes come from writing JSON like JavaScript. JSON does not allow trailing commas after the last item of an object or array; it requires double quotes around both keys and string values (single quotes are invalid); and it has no support for comments, undefined, NaN, or Infinity.

Other classics include unescaped control characters inside strings, missing commas between properties, and mismatched brackets in deeply nested structures. Because this formatter reports the precise position of the first violation — and Monaco underlines it in the editor — fixing even a large broken document becomes a sequence of quick, guided corrections rather than guesswork. For a verdict and nothing else, the JSON validator reports the same line and column without reformatting; for a payload that is too broken to parse at all, JSON Repair rewrites the mechanical mistakes first.

Format large JSON files offline, with no size limit

Server-backed formatters have to defend themselves: they cap request bodies, reject anything past a couple of megabytes, and sometimes queue your document behind other people's. This page has nothing to defend, because there is no server in the loop. The formatter is a static page whose parsing and printing happen in your tab, so the only ceiling is the memory your own browser is willing to hand the document. Multi-megabyte API dumps, database exports and bundled fixtures paste in and format; the ~5 MB figure on the upload dialog is friendly guidance, not an enforced cap, and dragging a bigger file in works the same way.

Being local also means being offline-capable: after the page and its editor have loaded once, formatting, validating, minifying, sorting keys and the tree view all keep working with the network switched off — useful on a plane, and useful in environments where pasting a payload into a website that phones home is not an option. The honest limit is memory rather than policy. A document is held in the editor, again as the formatted output, and again as the parsed object while node count and depth are measured, so peak usage runs to several times the file size; somewhere in the tens of megabytes a tab starts to feel slow and eventually gives up. Two practical habits: use the collapse control before exploring a very large tree instead of leaving every branch expanded, and reach for a streaming tool such as jq when a file is large enough that you would rather not hold it in a browser at all. For a quick size check, the stats bar reports the byte count, line count, node count and nesting depth of whatever is loaded.

Format API payloads and log lines

The most common reason to open this page is a payload someone just handed you: an HTTP response body copied out of the browser's network tab, the output of a curl call, a webhook body pasted into a ticket, a request that a client insists it sent correctly. Paste it in and it is re-indented immediately, with the exact position of the first syntax error if the copy went wrong — which it often does, because copied payloads arrive truncated, wrapped in a JSONP callback, or with the single quotes and trailing commas a colleague added by hand. The repair button handles that class of damage: it converts single quotes, drops trailing commas and comments, quotes bare keys, unwraps JSONP and completes a document that was cut off mid-copy, so a mangled payload usually becomes readable in two clicks.

Structured logs are the other everyday case. Loggers such as pino, bunyan, zap and Serilog — and anything that reaches CloudWatch or a Kubernetes log stream — emit one dense JSON object per line, which is unreadable in a terminal and perfectly readable here: paste a single line and the whole event, nested context and all, expands into an indented block. Do note that a log file is not one JSON document. Several objects stacked line by line is NDJSON, and a strict parser stops at the start of the second one, so format a line at a time or wrap the lines into an array first. To get a payload into the page there is an Upload button (drag and drop works too, for .json and .txt), and a URL loader that fetches an endpoint directly from your browser, which means the endpoint has to allow cross-origin requests since there is no server-side proxy to hide behind. Share does the reverse: it packs the document, compressed, into the link itself rather than storing it anywhere. Once the payload reads cleanly, the same document converts in one click to XML with repeated elements for arrays, to a flat CSV for a spreadsheet, or to YAML for a Kubernetes manifest.

Is it safe to format sensitive JSON here?

Yes. Unlike tools that send your input to a backend for processing, everything on this page happens locally in your browser. The parsing, validation, and formatting are pure client-side JavaScript; no request containing your data ever leaves your machine. That makes it appropriate for configuration files, API responses, and other payloads you wouldn't paste into an arbitrary website.

For regulated environments, the page also works offline once loaded, and the open, static architecture of the site means there is no hidden server-side processing to audit.

Help

Frequently asked questions

Everything you need to know about the JSON Formatter.

01How do I format JSON online?

Paste your JSON into the input editor (or click Sample to try it with example data). The formatter parses and re-indents it automatically as you type. Pick 2-space, 4-space, or tab indentation, then copy the result or download it as a .json file.

02Is my JSON uploaded to a server?

No. This formatter runs entirely in your browser using JavaScript — your data is never transmitted, logged, or stored anywhere. You can verify this by loading the page and switching off your network connection: the tool keeps working.

03Does this tool also validate JSON?

Yes. Every format operation is a full RFC 8259 parse. If your JSON is invalid, you get the exact line and column of the first error, both in the status bar and as a marker inside the editor, so you can fix it immediately.

04What indentation options are supported?

You can format with 2 spaces (the most common convention), 4 spaces, tab characters, or minify the document to a single line with all insignificant whitespace removed.

05How large a JSON file can I format?

The editor is built on Monaco — the same engine as VS Code — and comfortably handles multi-megabyte documents. The practical limit depends on your device's memory; documents in the tens of megabytes generally work fine on a modern machine.

06Does the formatter work offline?

Yes, once the page has loaded. The site is a static export and the formatting, validation, minifying, sorting and tree view all run as JavaScript inside your tab, so nothing needs the network after the initial load — switch off your connection and keep working, or leave the tab open on a flight. The one thing that needs a first-time download is the Monaco editor itself, which is fetched from a CDN and then served from your browser cache; loading JSON from a remote URL obviously needs a connection too. Uploading a local file, pasting, formatting and downloading do not.

07Can this tool fix invalid JSON automatically?

Yes — click the wrench icon to repair the input. It converts single quotes to double quotes, removes trailing commas and comments, adds quotes around bare keys, completes truncated documents, and strips JSONP wrappers. Always review the repaired result: the fixer makes the most reasonable interpretation of malformed input, but it can't read your mind.

08How do I filter or extract part of a JSON document?

Click the funnel icon to open the query bar and enter a JMESPath expression — for example items[*].name to pluck a field from every array element, or items[?price > `100`] to filter by value. The query runs against your input and writes the result to the output pane, entirely in your browser.

09Can I load JSON from a file or a URL?

Yes. Use the Upload button (or simply drag and drop a file onto the input editor) to load a local file, or click the URL icon to fetch JSON from any public endpoint. URL loading happens directly from your browser, so the remote server must allow cross-origin (CORS) requests.

10How do I share formatted JSON with someone?

Click Share to copy a link with your document compressed into the link itself — nothing is uploaded or stored on any server. Anyone opening the link sees the same JSON loaded in the formatter. Very large documents exceed what fits in a URL; download and send the file instead.

11What is the difference between formatting and minifying JSON?

Formatting (also called beautifying or pretty-printing) adds line breaks and indentation so humans can read the structure. Minifying does the opposite: it strips every unnecessary character to produce the smallest valid payload, which is what you want for production APIs and storage. This tool does both — choose 'Min' in the indent control or use the dedicated JSON Minifier.

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