JSON Validator
Validate JSON in your browser with precise line and column error reporting. Get a structural summary of valid documents. Free, no upload.
About this tool
Check whether a document is strictly valid JSON. Errors are reported with the line and column of the first problem: the missing comma, the trailing comma, or the single-quoted string.
Valid documents get a structural summary (root type, key count, size) so you can confirm the shape is what you expected, not just that it parses.
Common uses
- Verify a hand-edited config file before deploying it.
- Locate the exact syntax error a terse library error message hid from you.
- Sanity-check JSON produced by string concatenation or templates.
Automate via API
The same conversion is available as a REST endpoint for scripts, pipelines, and backends:
curl -X POST https://payloadly.com/api/v1/tools/json-validator \ -H "Content-Type: text/plain" \ -H "X-Api-Key: YOUR_API_KEY" \ --data-binary @input.json
Worked examples
Real payloads from tools people use daily, with the exact output this converter produces. Every example runs in your browser, so you can load one and adapt it to your own data.
Validate a package.json
A stray trailing comma in package.json breaks npm; this confirms the file is strictly valid before you run an install.
{
"name": "my-app",
"version": "1.0.0",
"scripts": { "build": "next build", "test": "vitest run" },
"dependencies": { "next": "^15.0.0" }
}Valid JSON. Root value : object with 4 keys Input size : 147 B (6 lines)
Validate a webhook payload
Before you write code against an incoming webhook, confirm the captured body is well-formed JSON and see its structural summary.
{
"id": "evt_1PabcXYZ",
"type": "charge.succeeded",
"data": { "object": { "id": "ch_3PabcXYZ", "amount": 2000, "currency": "usd" } }
}Valid JSON. Root value : object with 3 keys Input size : 140 B (5 lines)
JSON notes
JSON (JavaScript Object Notation) is the standard interchange format for web APIs, config files, and log pipelines. It is strict: keys must be double-quoted, trailing commas are invalid, and comments are not allowed.
- JSON does not support comments; they are stripped or rejected by parsers.
- Trailing commas after the last element are invalid JSON.
- Integers beyond 2^53 lose precision in JavaScript-based parsers.
Frequently asked questions
Is my data uploaded to a server?
No. This tool runs entirely in your browser using JavaScript, and there are no ads on the page. Nothing you paste or drop here is uploaded, logged, or stored, and you can verify that yourself: open your browser's developer tools and watch the Network tab while you convert (no requests leave the page), or disconnect from the internet after the page loads and keep working.
What JSON standard is enforced?
Strict JSON per RFC 8259, matching JavaScript's JSON.parse: double-quoted keys and strings, no comments, no trailing commas. JSON5 extensions are reported as errors, which is what you want when the target parser is strict.
Is there a size limit or a fee?
The browser tool is free with no signup and comfortably handles files up to tens of megabytes (limited by your device's memory). For automated or bulk processing inside your own scripts and pipelines, use the paid REST API.
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