JSON Validator
Free Online JSON Validator
About JSON Validator
JSON Validator is a precise, free online tool that checks whether your JSON string is syntactically valid according to the JSON specification (RFC 8259). It provides clear, actionable error messages that tell you exactly where a problem exists — down to the line number and character position — so you can fix it immediately.
Invalid JSON is one of the most common causes of API errors, broken configuration files, failed data imports, and application startup failures. Even a single misplaced comma, missing quotation mark, trailing comma after the last element, or unquoted key can cause an entire JSON document to be rejected by parsers. This validator catches all of these issues before they cause problems in your application.
Common JSON mistakes that the validator catches include: trailing commas after the last element in objects or arrays (not permitted in JSON, only in JSON5), single-quoted strings (JSON requires double quotes for all strings and keys), unquoted property keys (JSON requires all keys to be quoted strings), comments (JSON does not support // or /* */ comments), and undefined or NaN values (JSON only supports strings, numbers, booleans, null, objects, and arrays).
The validator uses the native JSON.parse() method built into modern browsers, which follows the ECMAScript specification implementation of RFC 8259. This means the same parser your JavaScript, Python, PHP, Ruby, Java, and Go code uses — giving you the most accurate validation possible. When validation fails, the error message includes precise position information so you spend zero time hunting for the problem.
Invalid JSON is one of the most common causes of API errors, broken configuration files, failed data imports, and application startup failures. Even a single misplaced comma, missing quotation mark, trailing comma after the last element, or unquoted key can cause an entire JSON document to be rejected by parsers. This validator catches all of these issues before they cause problems in your application.
Common JSON mistakes that the validator catches include: trailing commas after the last element in objects or arrays (not permitted in JSON, only in JSON5), single-quoted strings (JSON requires double quotes for all strings and keys), unquoted property keys (JSON requires all keys to be quoted strings), comments (JSON does not support // or /* */ comments), and undefined or NaN values (JSON only supports strings, numbers, booleans, null, objects, and arrays).
The validator uses the native JSON.parse() method built into modern browsers, which follows the ECMAScript specification implementation of RFC 8259. This means the same parser your JavaScript, Python, PHP, Ruby, Java, and Go code uses — giving you the most accurate validation possible. When validation fails, the error message includes precise position information so you spend zero time hunting for the problem.
starKey Features
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RFC 8259 Strict Validation
Validates JSON against the official JSON specification. Catches all common syntax errors including trailing commas, unquoted keys, single quotes, comments, and invalid escape sequences.
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Precise Error Location
When validation fails, the error message includes the exact line number and column position of the syntax error, making it trivial to locate and fix the problem in your editor.
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Real-time Validation as You Type
As you type or paste JSON, the validator checks it in real time and updates the status bar with immediate feedback. No button click needed for quick validation of short JSON strings.
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Valid JSON Formatted Preview
When JSON is valid, the tool displays a formatted, indented preview so you can visually confirm the data structure looks correct, not just that it parses without errors.
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Browser-based and Private
Validation runs entirely in your browser JavaScript engine. Your JSON data, API tokens, configuration values, and business records are never transmitted to any external server.
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Handles Large JSON Documents
Validates both small JSON snippets and large multi-megabyte JSON files. There is no artificial size limit imposed by the tool, only the memory available in your browser.
help_outlineHow to Use
1
Paste Your JSON
Paste the JSON string you want to validate into the input textarea. You can also upload a .json file using the file upload button in the panel header.
2
Click Validate
Press the Validate button or use Ctrl+Enter. The tool will immediately analyze your JSON and report whether it is valid or invalid.
3
Read the Error Message
If invalid, the status bar shows a detailed error message including the approximate line number and character position where the problem was detected.
4
Fix and Re-validate
Correct the identified issue in your JSON, paste the updated version into the input, and validate again. Repeat until you receive a green Valid JSON confirmation message.
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API Integration Validation
Validate request and response bodies before integrating with third-party APIs or before deploying your own API changes. Catch malformed JSON that would cause 400 Bad Request errors.
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Configuration File Verification
Verify that configuration files (package.json, tsconfig.json, .prettierrc, manifest.json) are valid JSON before committing them to version control or deploying to production.
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Debugging Parse Errors
When your application logs show a JSON parse error, paste the failing JSON here to immediately see exactly which character is causing the parser to fail.
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Learning JSON Syntax Rules
Beginners learning the JSON format can use the validator to understand exactly which syntax rules they are violating and why, accelerating mastery of the format.