Why does the validator show an error but I cannot see anything wrong?

Common invisible errors include a BOM (byte order mark) at the very start of the file that looks like empty space, zero-width non-breaking space characters inside strings pasted from Word or web browsers, and Windows-style line endings (CRLF) inside string values. Another frequent issue is a duplicate key — JSON technically allows duplicate keys but many validators flag them because parsers handle them inconsistently, sometimes taking the first value and sometimes the last.

Can I validate JSON against a JSON Schema with this tool?

The validator checks syntactic validity (well-formed JSON) rather than semantic validity against a schema definition. To validate JSON against a JSON Schema that enforces required fields, data types, and value ranges, you would need a dedicated JSON Schema validator tool or a library like Ajv in your project. Think of this tool as checking that the JSON can be parsed at all, while schema validation checks whether the parsed data matches your expected structure.

Does validating JSON files in the browser protect sensitive data?

Yes, the validator runs entirely client-side using JavaScript parsing — your JSON content is never transmitted to any server. This makes it safe to validate JSON files containing API keys, database credentials, user records, and other sensitive configuration data. As an additional precaution, close the browser tab when finished to ensure the content is not retained in browser session storage.

What are the most common JSON validation errors and how do I fix them?

The top errors are trailing commas after the last array item or object property (remove the comma), single quotes around strings (replace with double quotes), unquoted property keys like {name: 'value'} (add double quotes around the key), and control characters like raw tab or newline inside string values (replace with \t or \n escape sequences). The exact line and column number the validator reports points to where the parser failed, but the actual mistake is almost always in the immediately preceding character.

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JSON Validator

Validate JSON syntax and get precise error messages with line numbers.

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Input JSON

How to Use

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Paste your JSON

Paste the JSON you want to validate. The validator accepts any JSON structure — from simple key-value pairs to deeply nested API responses.

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Validate syntax

Click Validate to check your JSON. Errors are highlighted with the exact line, column, and a description of what went wrong. Fix issues and re-validate.

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Copy valid JSON

Once valid, copy the formatted JSON or download it. Use the validated data confidently in your application knowing it has correct syntax.

What is JSON Validator?

JSON Validator is a strict online validator that checks JSON documents for syntax errors and reports the exact line and column number where the problem occurs. Beyond standard JSON, it also supports JSON5 (which allows comments and trailing commas) and JSONC (JSON with Comments) used by VS Code configuration files. Developers, DevOps engineers, and technical writers use this tool to validate configuration files, API schemas, and data exports before deployment.

Why use JSON Validator?

Pinpointing the exact error location with line and column numbers saves hours of manually scanning large JSON files for a single misplaced comma or unclosed bracket. JSON5 and JSONC support means you can validate VS Code settings, TypeScript configs, and annotated data files without stripping comments first. The browser-based validator provides instant feedback with no round-trip latency and keeps confidential configuration data off third-party servers.

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How it works

DevOps engineers validate Kubernetes ConfigMaps and Helm chart values.json files before applying them to a cluster to catch errors that would cause silent deployment failures. Frontend developers validate their tsconfig.json and .eslintrc.json files using JSONC mode, which preserves the comments they use to document configuration decisions. API developers validate OpenAPI schema definitions and JSON Schema files before publishing documentation or running contract tests.

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Pro Tip

When validating JSON5 or JSONC files, make sure to explicitly select that mode — the validator will flag JavaScript-style comments as errors in strict JSON mode because they are genuinely invalid standard JSON. For very large JSON files, paste only the suspected problem section first to speed up error location, then validate the full document once the local issue is resolved.

Frequently Asked Questions

Strict JSON mode follows RFC 8259 exactly: keys must be double-quoted strings, trailing commas are forbidden, and comments are not allowed. JSON5 mode accepts single-quoted strings, unquoted keys that are valid identifiers, trailing commas, and JavaScript-style // and /* */ comments. JSONC mode accepts // and /* */ comments and trailing commas but still requires double-quoted string keys, matching the format used by VS Code configuration files.

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