JSON Validator
The JSON Validator checks whether a document is valid JSON. Paste your text and it validates as you pause — no button required. Valid input shows a green pass state with the character count; invalid input highlights the exact line and column and reports the expected token, which is far more readable than the raw "position N" from the browser. Validation runs locally in a Web Worker, so API payloads and configs stay on your machine, and 10MB files validate just as well.
How to use it
- 1
Paste or upload JSON
Paste the JSON you want to check, or drag and drop / pick a local .json file. The file is read on your machine only.
- 2
Pause to validate
About 300ms after you stop typing it parses in a Web Worker; during rapid edits only the latest result wins, so there is no flicker or false alarm.
- 3
Read the location
On error the whole line is highlighted, the gutter shows a marker, and the status bar reports "line X, column Y" with the expected token.
- 4
Fix and re-check
When the indicator turns green the JSON is valid. Then you can Format it for readability or open it in the tree view.
Key features
Continuous, automatic checks
Validation is debounced and runs in the background, so you always see the current status of the document.
Human-readable errors
Line and column plus a plain-language hint about the token that was expected — no more guessing from a byte offset.
In-line highlighting
The failing line is highlighted and the gutter is marked, so you can jump straight to the problem.
Stays local
Everything runs in the browser; sensitive payloads are never uploaded.
Scales to large files
Web Worker parsing keeps even multi-megabyte documents responsive.
One click onward
Valid JSON can be sent straight to the formatter, tree view or schema generator.
Common errors & troubleshooting
- ! Trailing commas after the last item are the single most common cause of "invalid JSON".
- ! Unquoted keys, single quotes and comments are all valid in JavaScript objects but not in JSON.
- ! A JSON document has exactly one root value — two top-level values need to be wrapped in an array.
- ! Unescaped control characters (raw newlines inside a string) also break parsing; escape them as \n.
Frequently asked questions
Does the validator send my JSON anywhere?
No. Parsing happens in a Web Worker inside your browser tab, so the data never leaves your device.
Is it the same as the browser console telling me about a position?
It is the same underlying parser, but this tool maps the error back to a line and column and explains what was expected, which is much easier to act on than a raw character position.
Does validation also format or change my JSON?
No. Validation only reports whether the document is valid and where it fails. Use the formatter when you want to re-indent the output.
Can it validate JSON Lines (NDJSON)?
The validator targets a single JSON document. For line-delimited logs, use the NDJSON tool, which validates each line and reports the exact line that failed.
Related tools
JSON Formatter
Format, beautify and validate JSON in your browser. Errors point to the exact line and column, and you can indent with 2 spaces, 4 spaces or a tab.
JSON to JSON Schema
Infer a JSON Schema from a sample JSON document, merging similar fields and marking required properties.
JSON Diff / Compare
Compare two JSON documents side by side. Additions, deletions and changes are colour-coded, and key or array order can be ignored.