JSON Validator Online
Paste your JSON and instantly check for syntax errors. Get exact line and column numbers, clear error messages, and a clean formatted result — free, private, and no sign-up required.
How JSON Validation Works
JSON (JavaScript Object Notation) follows a strict grammar defined in RFC 8259. Every value must be a string, number, boolean, null, object, or array. Object keys must be double-quoted strings. Trailing commas, single-quoted strings, comments, and undefined values are all illegal in standard JSON.
This JSON validator online uses the browser's native JSON.parse() engine to check your input against that grammar. When parsing fails, it extracts the error position and presents it alongside your original text so you can jump directly to the offending character. When parsing succeeds, it re-serializes the data with consistent indentation so you can visually confirm the structure is exactly what you expect.
Common JSON Errors and How to Fix Them
The most frequent cause of invalid JSON is the trailing comma — leaving a comma after the last element in an object or array. This is valid in JavaScript but illegal in JSON. Other common mistakes include using single quotes around strings or keys instead of double quotes, writing unquoted property names as you would in a JavaScript object literal, adding JavaScript-style comments ( // or /* */), and mismatched brackets or braces. If you are dealing with data from a legacy system or a loosely written API that produces these patterns, try the JSON Repair tool which can automatically correct many of these issues.
Frequently Asked Questions
What does a JSON validator do?
A JSON validator parses your JSON text and checks it against the official JSON specification (RFC 8259). It reports syntax errors — such as missing commas, unclosed brackets, unquoted keys, or illegal trailing commas — along with the exact line and column where each problem occurs. A valid result means your JSON is structurally correct and can be safely parsed by any standard JSON parser.
Why is my JSON showing a syntax error?
The most common JSON syntax errors are: trailing commas after the last item in an object or array, single-quoted strings instead of double-quoted strings, unquoted property keys, comments (which are not valid in standard JSON), and mismatched or missing brackets and braces. Paste your JSON into this validator and it will pinpoint the exact location of the problem so you can fix it quickly.
Is it safe to paste sensitive JSON data into this validator?
Yes. This JSON validator runs entirely in your browser using JavaScript. Your data is never transmitted to any server — it is processed locally on your device. This makes it safe to paste API responses containing tokens, internal configuration files, or any other sensitive data without risk of exposure.
What is the difference between JSON validation and JSON schema validation?
JSON validation checks that your text is syntactically correct JSON — proper brackets, quoted keys, valid value types, and so on. JSON Schema validation goes further: it checks that a structurally valid JSON document also conforms to a specific shape defined by a JSON Schema, such as required fields, value types, minimum/maximum constraints, and pattern matching. Use this tool for syntax validation; use the JSON Schema Generator to create a schema for structural validation.
Can this validator handle large or deeply nested JSON files?
Yes. The validator is built on the browser's native JSON parser, which can handle files with hundreds of thousands of lines and deeply nested structures without performance issues. For extremely large files (several megabytes), the initial paste may take a moment, but validation results appear immediately after parsing completes.