JSON Validator

What is a JSON Validator?

A JSON validator checks whether a piece of text conforms to the JSON specification (RFC 8259). Unlike a formatter which assumes valid input, a validator's primary job is to tell you exactly what is wrong and where — line number, column, and a clear error message — so you can fix it fast.

This validator supports three modes: strict JSON, JSONC (JSON with Comments, used by VS Code configs andtsconfig.json), and a relaxed JSON5 mode that additionally allows unquoted keys and single-quoted strings.

How to use this JSON Validator

1. Select your validation mode — Strict JSON, JSONC, or JSON5.
2. Paste your JSON into the input box, or drop a file. Validation is instant and updates as you type.
3. If invalid, the error panel shows the exact message and line/column number.
4. Click Attempt Fix to see a repaired version using jsonrepair.
5. Click Use repaired JSON to replace the input with the fixed version.

Why validate JSON with a private tool?

Config files, API payloads, and exported data often contain sensitive values — database credentials in config JSON, PII in API responses, proprietary schema structures. Pasting these into a server-side validator means your data is processed on someone else's machine and potentially logged. This validator runs entirely in your browser: the JSON never leaves your tab.

JSONC vs JSON5 — what's the difference?

JSONC (JSON with Comments) adds single-line (// …) and block (/* … */) comments, plus trailing commas after the last item. It is used by VS Code's settings.json, TypeScript'stsconfig.json, and many other developer tools.

JSON5 goes further: unquoted property names, single-quoted strings, hexadecimal numbers, multi-line strings, and positive/negative Infinity. It is less common but occasionally appears in Babel configs and custom serialisers.