JSON Validator — Check JSON Syntax Online

#What this tool does

This JSON validator parses your input using the standard JSON.parse() method. It catches syntax errors with position info: missing commas, trailing commas, unquoted keys, single quotes instead of double quotes, and malformed values.

All validation runs client-side in your browser. Nothing is sent to a server.

#Common JSON mistakes

// Trailing comma — invalid in JSON, valid in JavaScript
{"name": "app", "version": "1.0",}
 
// Single quotes — must be double quotes
{'key': 'value'}
 
// Unquoted keys — must be quoted
{key: "value"}
 
// Comments — JSON does not support comments
{"port": 3000 // default port}
 
// Missing comma between properties
{"host": "localhost" "port": 3000}

Every example above produces a parse error. The fix is always the same: follow the JSON spec strictly. Double-quoted keys, double-quoted strings, no trailing commas, no comments.

#JSON vs JSONC vs JSON5

JSON (RFC 8259) is the strict format. No comments, no trailing commas, keys must be double-quoted. Every API and data interchange format uses this.

JSONC is JSON with Comments. VS Code uses it for tsconfig.json, settings.json, and launch.json. Parsers like jsonc-parser strip comments before parsing. File extension is typically .jsonc.

JSON5 is a relaxed superset. Single quotes, trailing commas, unquoted keys, hex numbers, multiline strings, and comments are all valid. Useful for human-edited config files, but not for data interchange.

This validator checks strict JSON — the format your APIs and CI pipelines actually expect.

#When to use JSON

• API request and response bodies (Content-Type: application/json)
• Package manifests (package.json, composer.json)
• TypeScript config (tsconfig.json — technically JSONC, but the base syntax is JSON)
• Infrastructure config (Terraform .tf.json, CloudFormation templates)
• Data interchange between services and languages

#Related tools

Working with YAML instead? Try the YAML validator or convert between formats with YAML to JSON and JSON to YAML. For validating OpenAPI specs (which use JSON or YAML), see the OpenAPI validator.

#Open source

This tool is powered by @azin-tech/mini-tools, an open-source developer toolkit. View source on GitHub.