# JSON Validator — Find the Exact Syntax Error

> Check whether JSON is valid, with the precise position of the error and what usually causes it.

A JSON validator tells you not just that a document is invalid but where. This converts the parser's character offset into a line and column, shows the offending line with a caret under it, and names the likely cause — trailing comma, single quotes, unquoted key or a comment, which cover almost every real JSON error.

**URL:** https://convertto.tech/t/json-validator
**Category:** Data & Format Tools (https://convertto.tech/c/data-tools)
**Privacy:** Runs entirely in the browser; no upload
**Cost:** Free, no sign-up
**Last updated:** 2026-08-01

## Key facts

- **Privacy:** Runs entirely in your browser — nothing is uploaded
- **Cost:** Free, unlimited, no sign-up

## How to use

1. Enter or paste your json.
2. Choose the strictness.
3. Turn "Show a structure summary" on or off as needed.
4. Turn "Report duplicate keys" on or off as needed.
5. The result appears immediately — copy or download it.

## FAQ

### Why is a trailing comma invalid when every editor allows it?

Because the JSON specification does not permit one, and it never has. Editors and TypeScript accept them because JSON5 and JSONC do — those are supersets, not JSON. Anything sent over the wire to a strict parser will be rejected.

### My JSON has duplicate keys but still validates. Is that a problem?

It is valid but dangerous. JSON.parse keeps the last occurrence and drops the rest with no warning, while other languages differ — some keep the first, some error, some return both. If two systems read the same document they can legitimately disagree about its contents.

### Can this validate against a JSON Schema?

No — this checks syntax. If you need to check a document against a schema, generate the schema first with the JSON Schema generator and validate with a library in your own toolchain, where the schema lives alongside the code that depends on it.

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