Free JSON Validator

What Is a JSON Validator?

Quick answer: A JSON validator checks that text follows the JSON grammar so a program can read it. Paste your data above, press Validate JSON, and the page says JSON is valid or JSON is invalid. Validate your JSON now.

The check runs in your browser, so nothing you paste is sent anywhere, and there is no account to make. Use this JSON validator when an API response, webhook payload or config file stops loading and the log gives no hint where. It checks syntax, not meaning, so no JSON Schema is applied.

How to Validate JSON Online

1. Add your JSON. Type or paste it under Enter or paste JSON, use Load from URL with a public address, or pick a .json file. Files may be UTF-8, UTF-16 or Windows-1252.
2. Press Validate JSON. The browser's own JSON.parse gives the verdict, so there is no waiting on a server.
3. Read the panel. JSON is valid unlocks Save as TXT and Copy to Clipboard. JSON is invalid shows the parser message instead.
4. Fix and repeat. Correct the named line and check again.

Load from URL goes through our server and accepts public addresses only, so http://127.0.0.1/ gets That address is not allowed. The fetch stops at 3 MB and each visitor gets 20 loads a minute. Point it at an HTML page and the page source lands in the editor and reads as invalid, so check the address returns JSON. An empty box answers JSON is invalid with Paste or type some JSON first.

How to Read a JSON Parse Error

Take the usual culprit, a trailing comma in {"a":1,"b":2,}. The JSON error checker prints Parse error on line 1:, the offending line, a row of dashes with a caret under the problem, then Expecting 'STRING', got '}'. You get a line and a pointer, not a column.

Expecting lists what the grammar allowed, and got is what the parser found. In an array the same mistake lists every value the grammar would have accepted before got ']'. The echoed row may lose its line breaks, so trust the line number.

The quirk: for single quotes, unquoted keys, comments, NaN, undefined, +1, 0x1F, 01 and raw tabs the message ends in got 'undefined'. The caret points at or just before the problem; for 01 and 0x1F it marks the start of the number.

On multi-line input the reported line is the line of the last good token. A missing comma at the end of line 3 is reported on line 3, though the bad token starts on line 4. On a long response, paste a smaller slice into the box and halve it until the error shows up.

The Rules JSON Actually Enforces

Results from our own runs. The grammar is drawn out in the JSON grammar diagrams.

Rule of thumb: double quotes only, string keys, no comments, no trailing commas, and escaped control characters, so write \t instead of a real tab. Any top-level value is valid, because RFC 8259 dropped the old object-or-array requirement.

A byte order mark pasted as text gives an Unexpected token error on an invisible character, while a BOM file loaded with the file button is read correctly. JSON5 and JSONC are different formats, so a tsconfig with comments fails here.

Valid JSON That Can Still Bite You

Two cases pass the grammar and still get a warning under the green result.

Duplicate keys: {"a":1,"a":2} is accepted and the warning names the key. Many parsers keep the last value, though the spec leaves it open, so two systems can disagree.

Big numbers: 12345678901234567890 is valid, but JavaScript reads every number as a double precision floating point value, which keeps about 15 to 17 significant digits, so the tail of a long ID changes. Send IDs that large as strings.

What This Validator Does Not Check

This json validator checks syntax only, with no required fields or type rules. For JSON-LD, validate the syntax here, then run the markup through our Schema Markup Validator.

Pasted text and files stay in your browser; only Load from URL sends the address, not your text, to our server. We do not cut off pasted text, but a 3.8 MB array of 60,000 objects took about 8.6 seconds on one run and 5.2 on another in headless tests. The valid or invalid verdict comes from the same parser your own code calls, JSON.parse; the line and Expecting hints come from the editor's own parser.

Next Steps After Your JSON Validates

Our guide on how to format JSON online covers layout. Once the page says valid, these are the usual next stops.

• JSON Formatter: add indentation.
• JSON Viewer: open it as a tree.
• JSON Editor: change values, then validate again.
• JSON to XML converter: convert to XML.
• XML to JSON converter: convert back.
• XML Formatter: tidy the XML.
• All development tools: the full set.