Does validation upload my file?
No. Parsing runs in the browser.
jfmt.dev
JSON Validator
Paste a payload to check that it is valid JSON. Errors stay in this tab — we do not send documents to a server.
JSON formatter
Input
Output · preview.json
{ }
Run a tool to see a polished result here
What validation checks
The validator parses the document as JSON. If it is valid you get a confirmation and a formatted view. If not, the editor reports the syntax problem. Use Repair when you pasted JavaScript-style JSON with comments or trailing commas.
Sample input on this page
The editor is prefilled with a small example for JSON Validator. Validate checks JSON syntax in this tab and reports parse errors without uploading the payload. Replace it with your own file; the sample and your payload stay in this tab.
{
"service": "jfmt",
"enabled": true,
"nested": { "retries": 3, "tags": ["json", "local"] }
}How to use this tool
- Paste JSON into the JSON Validator editor. The file stays in this browser tab and is not uploaded to jfmt.dev.
- Click Run. Validate checks JSON syntax in this tab and reports parse errors without uploading the payload.
- Copy the output, or continue with a related tool below. Related tools on this site include beautify, validate, minify, JSON to CSV, JSON to YAML and JSON to XML — all local.
- JFmt runs in a Web Worker in this tab. Do not paste production secrets if you share your screen.
When this page is the right choice
This dedicated JSON Validator URL matches that search intent; the homepage stays the general formatter. Validate checks JSON syntax in this tab and reports parse errors without uploading the payload. Related tools on this site include beautify, validate, minify, JSON to CSV, JSON to YAML and JSON to XML — all local. JFmt runs in a Web Worker in this tab. Do not paste production secrets if you share your screen. Read errors in the output pane instead of sending production payloads to another service.
Related tools
FAQ
Can it fix invalid JSON?
This page starts in validate. Switch to Repair in the sidebar to attempt automatic fixes.
Are duplicate keys reported?
Yes when the parser detects them. JSON officially allows only unique keys.
Does this tool upload my file?
No. Parsing and conversion run in a Web Worker in this tab. jfmt.dev does not receive the payload.
Why is there a separate URL from the homepage?
So people searching for this operation land on a page that already selects it. Validate checks JSON syntax in this tab and reports parse errors without uploading the payload.