JSON Validator
Validate JSON data and get detailed error messages pointing to the exact location of syntax errors.
About the JSON Validator
A JSON validator and formatter parses, checks, and validates JavaScript Object Notation (JSON) payloads against standard RFC 8259 specifications. JSON is the universal data interchange format for modern REST APIs, web microservices, and database configurations.
When APIs reject requests with cryptic parse errors, this tool identifies syntax mistakes—such as missing quotes around keys, trailing commas after the last array item, unescaped control characters, or mismatched brackets—pointing directly to the exact line and column number of the error.
In addition to syntax verification, the tool beautifies minified JSON with customizable 2-space or 4-space indentation, or minifies human-readable JSON into a compact single line to reduce network payload sizes.
Pasting an API response containing a trailing comma `{"id": 1, "name": "Tool",}` immediately flags: "SyntaxError: Unexpected token '}' at line 1, column 28: trailing comma is not permitted in valid JSON."
Tips for best results
- Remember that all JSON string values and object property keys must use double quotation marks ("); single quotes (') are invalid JSON syntax.
- Never include trailing commas after the final element in JSON arrays or objects; while permitted in JavaScript, they violate strict JSON specifications.
- Client-side validation ensures that sensitive API keys, customer payloads, and database records pasted into the validator are never transmitted to external servers.
How to use the JSON Validator
Why use Toolseza for JSON Validator?
Use this tool as often as you need with no paywalls, premium tiers, or hidden daily calculation quotas.
All calculations and file manipulations run inside your web browser. Your inputs are never sent to a cloud server.
Results update in real-time as you type or adjust settings, with instant one-click copy and export capabilities.
Works natively on smartphones, tablets, laptops, and desktop computers with zero installation or account creation.
Editorial Standards & Verification: All formulas, algorithms, and conversion factors implemented on Toolseza adhere to openly documented international standards (ISO, NIST, BIPM, W3C). Results are verified against benchmark reference datasets before publication.
Frequently Asked Questions
Is JSON Validator free to use?
Yes — JSON Validator is completely free, unlimited, and requires no sign-up.
What are the most common JSON errors?
Common errors include trailing commas after the last item, unquoted keys, single quotes instead of double quotes, and missing or mismatched brackets and braces.
Does the output follow the standard spec?
Yes — output follows the standard format, so it's compatible with other tools and libraries.
Does it work on mobile and tablet?
Yes — JSON Validator works on any modern browser, including mobile and tablet, no app required.