JSON Validator

A JSON validator parses your input against the strict JSON grammar defined in ECMA-404 and RFC 8259. It confirms that braces and brackets are balanced, every key is a double-quoted string, every string is properly terminated, every number is well-formed, and the top-level value is a valid JSON value. If parsing succeeds, the document is guaranteed to be loadable by any compliant JSON parser in any language.

A formatter focuses on rewriting valid JSON (beautify, minify, sort). A validator focuses on diagnosis: it pinpoints the exact line and column of the first error, shows a caret pointing at the offending character, lists likely causes (trailing comma, single quotes, comments, unquoted key), and reports structural stats like depth, key count, and duplicate keys. Use the validator when something is broken; use the formatter when it already parses.

The browser's parser reports the first character it cannot legally accept. The five most common causes are: a trailing comma after the last item in an object or array, a single quote where a double quote is required, an unquoted property name, a missing closing brace or bracket, and a stray character (BOM, smart quote, non-breaking space) pasted in from a word processor. The validator highlights the line and column so you can jump straight to it.

Yes. JSON.parse silently keeps only the last value when a key is repeated inside the same object, which can hide bugs. This tool scans the raw source and reports every duplicate key it finds — useful when you suspect an API or a configuration file is dropping values unexpectedly.

No. This validator follows strict JSON, so it rejects // and /* */ comments, trailing commas, single-quoted strings, and unquoted keys. If you are working with JSON5 or JSONC, the validator will flag exactly which non-standard features are present so you can strip them before passing the payload to a strict parser.

No. All parsing, error detection, and structural analysis happens entirely in your browser using JSON.parse. Your data never leaves your device, which makes the validator safe for inspecting API responses, configuration files, JWT payloads, or anything else that may contain secrets.

After successful validation the tool reports the byte size, line count, maximum nesting depth, total number of keys, and a breakdown of how many objects, arrays, strings, numbers, booleans, and nulls the document contains. These figures help you spot oversized payloads, unexpectedly deep nesting, or schema drift between two versions of the same response.

Yes, within the limits of your browser's memory. Multi-megabyte payloads validate in milliseconds on a modern device. For extremely large files (tens of megabytes or more) a streaming command-line tool like jq is more efficient, since browser parsers load the whole document into memory at once.

Not yet. This tool checks syntactic validity (is it well-formed JSON?), not semantic validity against a schema (does it match a contract?). For schema validation, look for a JSON Schema validator that accepts a Draft 2020-12 schema along with the instance document.