JSON Validator and Formatter: Client-Side, No Data Sent
Validate and format JSON. Nothing leaves your browser.
This JSON validator and formatter runs entirely in your browser. Your JSON never leaves your device, which matters when your payload contains API keys, tokens, or private data. Paste any JSON to instantly validate syntax, pinpoint errors with line and column numbers, and format with your preferred indent size. No account needed. No data sent.
1| {
2| "user": {
3| "id": 12,
4| "name": "Sam"
5| },
6| "active": true
7| }All parsing and formatting runs in your browser. No payload is sent to a server.
How this tool works
The tool passes your input to the browser's built-in JSON.parse() engine. If parsing succeeds, it runs JSON.stringify() with your chosen indentation width (2 spaces, 4 spaces, or tab) to produce formatted output. If parsing fails, it captures the native error message and extracts the reported character offset, then converts that offset to a line-and-column reference so you can find the problem immediately. The validator checks for strict JSON compliance per RFC 8259: quoted keys, no trailing commas, no comments, no undefined or NaN values, and properly escaped strings. It does not attempt to repair or auto-correct your input. The formatter preserves the original key order of your objects and does not alter string values or numbers in any way.
Worked example
A raw API log contains: {"user_id":1042,"roles":["admin","viewer"],"active":true,}. The trailing comma after true makes this invalid JSON. The tool reports: Parse error at line 1 - Unexpected token } - trailing commas are not allowed in JSON. After removing the comma, the tool returns a cleanly indented JSON block. The payload is never sent anywhere; it exists only in your browser's memory.
Frequently asked questions
Is my JSON sent to a server?
No. The tool runs entirely in your browser using the JavaScript engine built into the page. When you paste JSON and click Format, there is no network request. You can verify this by opening your browser's DevTools Network tab while using the tool: you will see no outbound requests carrying your payload.
Why is the reported line or column number sometimes off by one?
The line-and-column reference is derived from the character offset reported by JSON.parse(). If your text uses Windows-style CRLF line endings instead of Unix-style LF, each line ending counts as two characters in the offset but one visible line break. Look one character before or after the reported position if you cannot find the error at the exact spot.
Does it validate against a JSON Schema?
No. This tool checks structural validity only: is this valid JSON per RFC 8259? It does not check whether values conform to a schema (required fields, correct types, value ranges). Use this tool to confirm the JSON is parseable, then run schema validation separately in your application code.
Why use this over the browser's built-in DevTools console?
This tool gives you a dedicated input area, instant formatting on paste, a copy-to-clipboard button, and plain-English error messages with line numbers. The browser console requires opening DevTools, typing JSON.parse() with your payload escaped inside a string literal, and reading collapsed output. This tool is faster for one-off debugging.
What is the maximum input size?
There is no hard limit imposed by the tool. In testing, payloads up to 5 MB format without issue in modern browsers. Very large payloads (50 MB or more) may cause the tab to freeze briefly. If you routinely work with payloads that large, a local command-line tool like jq will be faster.
Does it handle Unicode, emoji, and non-ASCII characters?
Yes. JSON natively supports Unicode. The tool preserves all Unicode characters in string values as-is, including emoji, CJK characters, Arabic, and any other codepoint. Characters can also appear as JSON Unicode escape sequences and the tool displays them in their escaped form without converting.