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jsonblocks

Free online JSON validator

Paste JSON to check it locally. This free JSON validator reports exactly which line and column broke the parse, shows the offending line, and suggests the most likely fix - all locally in your browser.

Input

Valid JSON

Verdict

Valid JSON

Keys
5
Depth
3
Nodes
8
  • 3 string
  • 1 number
  • 1 boolean
  • 1 null
  • 1 object
  • 1 array

Checked with the built-in JSON parser as you type. Everything runs locally; nothing is uploaded.

How to validate JSON with jsonblocks

  1. Paste your JSON into the input panel or load a sample.

  2. Read the verdict at the top: valid documents show a key and depth summary.

  3. For invalid JSON, read the highlighted line and the suggested fix.

  4. Correct the error and re-paste, or open the document in the visualizer.

Frequently asked questions

How do I know if my JSON is valid?

Paste it above. Valid JSON gets a green verdict plus a summary of keys, depth, and value types. Invalid JSON gets the exact line and column of the first syntax error with a plain-language explanation.

What are the most common JSON errors?

Trailing commas after the last item, single quotes instead of double quotes, unquoted object keys, comments, and truncated pastes. The guide on fixing invalid JSON walks through each one with examples.

Does JSON allow trailing commas?

No. Standard JSON rejects trailing commas, unlike JavaScript object literals. If your error points at a closing brace or bracket, a stray comma just before it is the most likely cause.

Can I validate a large JSON file?

Yes. Paste large documents directly or open a .json file on the homepage, where parsing runs in a background worker so the tab stays responsive.

Does the validator check JSONL or JSON with comments?

This validator checks standard JSON only. JSONL (one object per line) and JSONC (JSON with comments) need dedicated parsers; pasting them here will report the first line that is not plain JSON.

Is my JSON uploaded anywhere?

No. Validation runs entirely in your browser with the built-in JSON parser. Nothing is sent, stored, or logged, so API keys and private payloads stay on your machine.