About this tool
Parsers love to report errors as a single character offset, which makes them nearly useless when you are staring at a wall of JSON on screen.
DataFmt's JSON Validator maps parse errors to line and column numbers, and for valid input shows a concise structural summary: the top-level type, number of keys, array length and maximum nesting depth — enough to tell in seconds whether the shape matches your expectations.
How to use
- Paste the JSON you want to check.
- Click "Validate".
- If valid, review the green summary block.
- If invalid, jump to the reported line and column and fix the issue.
Use cases
- Verify that API responses and webhook payloads are well-formed before debugging the business logic.
- Guard generated JSON artefacts in CI to catch malformed output early.
- Teach newcomers JSON by making object and array nesting visible.
Notes
- Strict JSON rules apply: no comments, no trailing commas, keys must be double-quoted.
- The summary is computed only for valid input.
- Very large inputs still validate; summary time scales linearly with size.
Frequently Asked Questions
Does "valid" mean "correct"?
It only means syntactically valid. For field-level validation use JSON Schema.
My JSON parses elsewhere but fails here — why?
Some parsers are lenient (trailing commas, comments). This tool follows the spec strictly; fix the input for maximum compatibility.
What is "max depth" in the summary?
The deepest chain of nested objects/arrays from root to leaf. Very deep nesting often hints that the schema should be flattened.