JSON Validator

What is JSON Validator?

The JSON Validator catches malformed JSON before it bites you downstream. Generic engine errors are not very helpful, so we run a hand-rolled tokenizer that pinpoints the exact line, column and reason for every problem it finds.

How it works

We tokenize the input character-by-character, expecting the RFC 8259 grammar (object, array, string, number, true/false/null). When something is off — a trailing comma, a single-quoted string, an unquoted key — we record the exact position and continue scanning so multiple errors are listed in one pass.

1. Paste or drop JSON. Drop a file or paste text. Validation runs on every keystroke (debounced).
2. Read the error list. Each error is shown with its line, column and a plain-English reason. The error count and a Valid / Invalid badge are announced via a live region for screen readers.
3. Fix and re-validate. Edit in place — the errors update as you type.

Examples

Trailing comma

{ "a": 1, } is reported at line 1, column 9: "Trailing comma not allowed in strict JSON."

Single-quoted string

{ 'a': 1 } is reported at line 1, column 3: "JSON strings must use double quotes."

Common mistakes

Mixing JSON with JSONC / JSON5

Strict JSON forbids comments and trailing commas. If your source is JSONC (for example VS Code settings.json), use a converter first.

BOM in the file

Some editors prepend a UTF-8 BOM (\uFEFF). The Validator will surface it as an unexpected character at position 0.

Alternatives

JSON Formatter

If your JSON is valid and you want it pretty-printed, jump straight to the Formatter.

JSON Schema Validator

For checking JSON against a schema (not just RFC validity), use the Schema Validator (coming soon).

Frequently asked questions