JSON Validator – Online Syntax Checker & Linter

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Online JSON Validator & Syntax Checker — Guide & Error Diagnostics

Identify and debug JSON syntax errors instantly. Get precise diagnostic feedback on syntax issues like unclosed quotes, missing commas, unescaped characters, or illegal trailing commas.

When to use this tool

Debug broken REST or GraphQL API payloads before integrating with frontend components
Validate hand-edited configuration files (`package.json`, `tsconfig.json`, `.eslintrc.json`)
Verify syntax compliance of Webhook payload templates before registering endpoints
Fix common copy-paste syntax errors (single quotes, trailing commas, unescaped newlines)

Common JSON syntax errors

Trailing Commas: Standard JSON does not permit trailing commas after the last object property or array item.
Single Quotes: JSON keys and string values must strictly use double quotes ("key").
Unescaped Newlines: Multi-line strings in JSON require \n escaping.
Missing Quotes on Keys: Unquoted keys (e.g. { name: "Alex" }) are invalid in JSON.

Related tools

Format validated JSON into clean code with JSON Formatter, or convert validated JSON objects into TypeScript interfaces using JSON to TypeScript Generator.

Frequently Asked Questions

Common questions about this tool.

How does Nadhebe JSON Validator detect syntax errors? ▼

The validator parses input strings against the strict ECMA-404 JSON specification using native browser JSON parsing and AST analysis, highlighting exact error line numbers, character positions, and expected tokens.

Can I format and fix JSON while validating? ▼

Yes! Click "Format / Beautify" to automatically structure, fix quotes, and format your JSON while validating its syntax.

Why are trailing commas disallowed in JSON? ▼

Unlike JavaScript objects, the JSON standard explicitly forbids trailing commas after the last array item or object key-value pair. Trailing commas cause `SyntaxError: Unexpected token` in standard JSON parsers.

Why does single-quoted JSON throw a validation error? ▼

Standard JSON requires all property names and string values to be enclosed in double quotes (`"key"`). Single quotes (`'key'`) are invalid syntax per RFC 8259.

Is client-side JSON validation safe for private API responses? ▼

Yes. Validation happens 100% locally inside browser memory. Your confidential API keys, payload data, and tokens are never transmitted to external servers.