# Find the exact character where your JSON breaks

"Unexpected token < in JSON at position 1" tells you almost nothing when position 1 is inside a 200 MB file. JSONParse reports the line, the column and the text around the failure.

## What you get when a parse fails

- The **byte offset** of the offending character.
- The **line and column**, computed from a line-start table built during the scan.
- A description of what the parser expected at that point.
- The surrounding source, so you can see whether it is a truncated download, an HTML error page, a trailing comma or a smart quote.

## The failures that actually happen

| Symptom | Usual cause |
| --- | --- |
| Fails at position 0 or 1 with `<` | The response is an HTML error page, not JSON. Check the status code. |
| Fails near the very end | Truncated download or an interrupted write. Compare the byte count with `Content-Length`. |
| Fails after a value, before `}` | A trailing comma — legal in JavaScript, not in JSON. |
| Fails on a string | A smart quote pasted from a document, or an unescaped control character. |
| Parses only the first object | The file is newline-delimited, not a single document. See [JSONL](/jsonl-viewer). |
| `NaN`, `Infinity` or `undefined` | A serialiser emitted JavaScript rather than JSON. |

## Validating structure, not just syntax

Syntax validation answers "is this parseable". It does not answer "is this the right shape". For that, generate a [JSON Schema](/json-schema-generator) from a document you trust and validate later documents against it in CI.

[Open the viewer](https://jsonparse.online/)

## Frequently asked questions

### Does the validator stop at the first error?

Yes. JSON has no recovery rule that is safe to guess at — once a document is malformed, everything after the failure point is ambiguous. The first error is reported precisely rather than a list of speculative ones.

### Can it validate against a JSON Schema?

Not in the viewer today. JSONParse generates a schema from a document; validating documents against an existing schema is best done with a dedicated validator such as Ajv in your build or test pipeline.

### Why does my file validate here but fail in my application?

Most often the application is stricter about duplicate keys, very large integers, or a specific top-level type. It can also be reading the file with a different encoding — a UTF-8 BOM ahead of the opening brace breaks several parsers.

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Source: https://jsonparse.online/json-validator
Last updated: 2026-09-14
JSONParse — Read, search and type huge JSON in your browser