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Validate and format JSON data
Validate and format JSON data instantly with our free online JSON validator. This tool helps developers and API users verify JSON syntax, identify errors, and beautify JSON for better readability. Simply paste your JSON data and get instant validation with formatted output.
JSON (JavaScript Object Notation) is a lightweight data interchange format. This validator checks if your JSON is properly formatted according to the JSON specification.
Common errors:
JSON validation checks whether a string is syntactically correct JSON and optionally validates against a schema. Valid JSON must follow strict rules: double-quoted strings, no trailing commas, no comments, and proper value types. Validation catches errors before they cause runtime failures in your applications.
The validator parses the input using JSON.parse(), which throws a SyntaxError for invalid JSON. The error message indicates the character position where parsing failed. Advanced validators also check against JSON Schema to validate structure, data types, required fields, and value constraints.
JSON syntax rules (RFC 8259): Strings must use double quotes ("not 'single'). Objects use {key: value} with string keys. Arrays use [value, value]. Values can be: string, number, object, array, true, false, null. Numbers cannot have leading zeros (except 0.x), cannot be NaN/Infinity. No trailing commas allowed.
Validate request bodies before processing to prevent malformed data errors.
Reject {"name": 'John'} because single quotes are invalidValidate JSON config files in CI/CD pipelines before deployment.
Verify JSON data files before importing into databases or applications.
Validate JSON submitted from web forms or API clients.
Validate JSON log entries to catch logging errors.
function isValidJSON(str) {
try {
JSON.parse(str);
return { valid: true };
} catch (e) {
return {
valid: false,
error: e.message,
position: e.message.match(/position (\d+)/)?.[1]
};
}
}
// Usage
const result = isValidJSON('{"name": "John"}');
// { valid: true }JSON.parse throws SyntaxError for invalid JSON. The error message often includes the position where parsing failed.
import json
def validate_json(json_string):
try:
json.loads(json_string)
return {"valid": True}
except json.JSONDecodeError as e:
return {
"valid": False,
"error": str(e),
"line": e.lineno,
"column": e.colno
}
# With schema validation (jsonschema library)
from jsonschema import validate, ValidationError
schema = {
"type": "object",
"required": ["name", "age"],
"properties": {
"name": {"type": "string"},
"age": {"type": "integer", "minimum": 0}
}
}
validate(instance=data, schema=schema)Python's JSONDecodeError provides line and column numbers. Use jsonschema library for schema validation.
Use JSON validation whenever you receive JSON from external sources: API requests, user uploads, third-party integrations, configuration files. Essential for preventing runtime errors and data corruption.
1) Trailing commas: {"a":1,} 2) Single quotes: {'key': 1} 3) Unquoted keys: {key: 1} 4) Comments: {"a":1 //comment} 5) Missing quotes on strings: {name: John} 6) Single values not wrapped: just hello instead of "hello"
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