Developer Tools
JSON Validator: Check JSON Syntax Online
Check whether your JSON is valid and locate errors.
Runs locally in your browser — your input is not uploaded.
What is this tool?
Paste any JSON document and the validator tells you whether it is syntactically correct. When it is not, you get the parser’s error message mapped to a line and column, so you can jump straight to the problem instead of scanning the whole file.
A JSON validator checks that text conforms to the JSON grammar. It does not check whether the data matches a particular schema — only that it is syntactically valid.
When the JavaScript parser reports a character position, ToolForge maps that position back to a line and column so you can jump to the problem quickly.
Validation happens locally. Your payload is never transmitted to ToolForge.
How to use the JSON Validator
- Paste the JSON you want to check, or upload a .json file.
- Click Validate.
- If the document is invalid, read the error message and the line/column hint.
- Fix the issue and validate again until it passes.
Examples
Catch a trailing comma
This document is invalid because of the comma after 2.
{"a":1,"b":2,}Frequently asked questions
Does this validate against a JSON Schema?
No. This tool checks syntax only. Schema validation is a separate concern and may be added in a future premium tool.
Why might line numbers be approximate?
Browsers expose different error message formats. When a character position is available we convert it to line/column; otherwise we show the raw parser message.
What are the most common JSON syntax errors?
Trailing commas, single-quoted strings, unquoted keys, comments, and missing commas between items. JavaScript objects allow some of these, but strict JSON does not.
Is my JSON sent anywhere?
No. Validation uses your browser’s built-in JSON parser, so the document never leaves your device.
Want more power later?
Premium tools, higher limits, and API access are on the roadmap. V1 stays free and private in your browser.