JSON Validator.

Validate JSON online — find errors instantly

A JSON validator tells you whether a document is well-formed JSON and, when it is not, exactly where it breaks. Paste your JSON above and press Validate JSON: the tool parses it locally and reports either “Valid JSON” with key, array, and depth counts, or the precise line and column of the first syntax error.

Common JSON errors this catches

• Trailing commas after the last item in an object or array.
• Single quotes or unquoted keys — JSON requires double quotes.
• Mismatched brackets and [ ].
• Comments, which standard JSON does not permit.
• Smart quotes and stray characters pasted from documents.

What the error messages actually mean

JSON parser errors are terse and unhelpful until you know the pattern behind each one. These four cover almost everything you will hit:

Unexpected token } in JSON at position 42 — a trailing comma. JavaScript happily accepts { "a": 1, }; JSON forbids it, so the parser reaches the } while still expecting another key.

Expecting property name enclosed in double quotes — unquoted keys or single quotes. Your text is a Python dict or a JavaScript object literal, not JSON. Every key and every string value needs double quotes.

Unexpected end of JSON input — the document is truncated, leaving braces unclosed. Usually a partial download, or an LLM that hit its token limit.

Unexpected token N / T in JSON — Python's None, True, or NaN. JSON knows only null, true, and false, all lowercase.

“But my JSON looks fine!” — the invisible causes

When the error position points at something that looks perfectly correct, the culprit is nearly always something you cannot see:

• Smart quotes. Text pasted from Word, Notion, or a chat window arrives with “curly” quotes instead of "straight" ones. They look almost identical and are not valid JSON.
• A BOM. An invisible byte-order mark at the very start of the file, courtesy of Windows Notepad or an Excel export.
• Comments. Strict JSON has no comment syntax — not //, not /* */. Config files that look like JSON are often JSON5 or JSONC, which do allow them.
• A real tab or newline inside a string. These must be escaped as \t and \n, not embedded literally.

All four are fixed automatically by the JSON repair tool — send your input there rather than hunting for an invisible character by eye.

Syntax validation vs schema validation

These are two different jobs and people conflate them constantly. This page does syntax validation: is this parseable JSON at all?

It cannot tell you whether { "age": "twenty" } is wrong — that is perfectly valid JSON syntax, just the wrong type for your data. Checking that age must be a number, that email is required, or that status must be one of three values is schema validation. For that, build a contract with the JSON Schema generator.

Do them in order: valid syntax first, correct structure second.

Validate privately, then keep working

Validation runs entirely client-side, so it is safe for sensitive data. Once your JSON checks out, format it for readability, minify it for production, or explore it as a tree. New to the format? Read common JSON errors and how to fix them.

Validating each file first also makes a merge predictable: if you plan to combine several JSON files into one, a single malformed input is the usual reason the whole operation fails, and it is far easier to find the bad line here than in the combined output.