JSON Validator
100% privateFree online JSON validator — check JSON syntax instantly, detect errors with exact line and column numbers. Supports schema validation. 100% browser-based.
Paste JSON above and click Validate.
This free online JSON validator checks whether your JSON is syntactically valid and reports errors with precise location information — line number, column, and a human-readable description of what went wrong. When the JSON is valid, the tool reports the root type, total key count, and nesting depth so you can understand the structure at a glance. All validation runs in your browser using JSON.parse(); your data is never sent to any server.
Beyond basic syntax checking, this JSON validator and formatter handles the most common errors developers encounter: trailing commas, unquoted keys, single-quoted strings, and missing colons. For developers working with Swagger / OpenAPI JSON specifications, JSON-LD structured data (ld+json), or FHIR medical JSON resources, syntax validation is the essential first step before applying a JSON Schema validator. Unlike JSONLint.com, this online JSON validator tool also displays structure metadata — root type, nesting depth, and key count — for any valid document.
Whether you are debugging a Python json.loads() failure, validating an API response payload, or checking a configuration file before deployment, this tool gives you instant feedback with no rate limits, no file size restrictions, and no account required. For structural validation beyond syntax — enforcing required fields, data types, and value constraints — use a JSON Schema validator with Ajv (Node.js) or the jsonschema package (Python) against a schema definition.
How It Works
- Paste your JSON string or document into the input field
- Validation runs instantly — syntax errors are reported with line and column numbers
- For valid JSON, the tool displays the root type, total key count, and maximum nesting depth
- Fix the reported error and re-validate until the document is fully clean
Features
- Instant JSON syntax validation using JSON.parse() — strict ECMA-404 / RFC 8259 standard
- Precise error location: line number, column number, and human-readable error description
- Structure metadata for valid JSON: root type, key count, and maximum nesting depth
- Detects all common errors: trailing commas, unquoted keys, single-quoted strings, mismatched braces
- No file size limit — bounded only by available browser memory
- 100% browser-based — your JSON never leaves your device
- Works with API responses, config files, Swagger specs, JSON-LD, and FHIR documents
Examples
Valid JSON
Input
{"name":"Alice","age":30,"skills":["TypeScript","Go"]}Output
✅ Valid JSON
Type: object | Keys: 3 | Max depth: 2Invalid — trailing comma
Input
{"name":"Alice","age":30,}Output
❌ SyntaxError: Unexpected token } at line 1, column 26Common Use Cases
- Debugging json.loads() failures in Python or JSON.parse() errors in JavaScript and Node.js
- Validating API response payloads before parsing them in your application
- Checking Swagger / OpenAPI JSON specifications for syntax errors before loading them in tools
- Validating JSON-LD structured data (ld+json script tags) for Google rich result eligibility
- Inspecting FHIR JSON resources for basic structural validity before schema validation
Developer Tips
- Trailing commas are the #1 JSON error — remove the comma after the last item in any array or object; they are valid JavaScript but illegal in strict JSON
- All JSON string keys must be double-quoted — single-quoted keys and unquoted identifiers are valid JavaScript but invalid JSON
- For structural validation beyond syntax, use Ajv (Node.js) or the jsonschema package (Python) with a JSON Schema definition — the schema enforces required fields, types, and value ranges
- For large JSON files (>10MB), validate offline: python -m json.tool file.json or node -e "JSON.parse(require('fs').readFileSync('file.json','utf8'))"
Frequently Asked Questions
- How do I use a JSON Schema validator?
- A JSON Schema validator checks not just that your JSON is syntactically valid but also that it matches a defined structure — required fields, data types, value ranges, and allowed patterns. To use one: define your schema as a JSON document using the JSON Schema specification (draft-07 or 2020-12), then validate your data against it. In Node.js, use the Ajv library: const ajv = new Ajv(); const validate = ajv.compile(schema); const valid = validate(data). In Python, use the jsonschema package: jsonschema.validate(data, schema). This online JSON validator handles syntax only — use those libraries for schema validation.
- What makes JSON invalid?
- Common JSON syntax errors include: trailing commas after the last element (invalid in JSON, unlike JavaScript), unquoted property keys (all keys must be double-quoted strings), single-quoted strings (only double quotes are valid), comments (JSON has no comment syntax — use JSON5 or JSONC for that), undefined or NaN values (not valid JSON types), and unmatched brackets or braces. This validator reports the exact line and column of the first error found.
- What is the difference between JSON and JavaScript objects?
- JSON is a strict data interchange format derived from JavaScript object syntax with important restrictions. JSON requires double-quoted string keys, disallows trailing commas, has no comment syntax, and only permits these value types: strings, numbers, booleans (true/false), null, arrays, and objects. JavaScript objects are more permissive — they allow single quotes, unquoted keys, trailing commas, functions, undefined, and Symbol keys. JSON.parse() rejects any input that is not strict JSON (ECMA-404).
- Does valid JSON mean correct data?
- No. JSON validation only checks syntax — whether the document conforms to the JSON grammar. A syntactically valid JSON document can still have incorrect data: wrong types for expected fields, missing required fields, or values outside allowed ranges. For structural data validation, use a JSON Schema validator such as Ajv (Node.js) or jsonschema (Python), which lets you specify the expected structure, required properties, types, and constraints.
- Can I validate very large JSON files?
- Yes. Validation runs locally in your browser with no server-imposed size limit. For extremely large files (50MB+), performance depends on your device's available memory. Paste the JSON directly into the input field. For very large files, consider using command-line validation instead: python -m json.tool largefile.json or cat largefile.json | node -e "process.stdin.resume();process.stdin.setEncoding('utf8');let d='';process.stdin.on('data',c=>d+=c);process.stdin.on('end',()=>JSON.parse(d))".
- What is the difference between JSON and JSON5?
- JSON5 is an extension of the JSON format that relaxes several strict rules: it allows comments (// and /* */), trailing commas, single-quoted strings, unquoted object keys, and hexadecimal numbers. JSON5 is not a standard and is not accepted by most APIs or parsers expecting strict JSON. This validator checks against the strict JSON standard (ECMA-404 / RFC 8259). Use a dedicated JSON5 linter if you are working with JSON5 configuration files.