Validate JSON Using PHP

JSON validation is essential when working with APIs, configuration files, or any data exchange in PHP. Invalid JSON can cause errors, security issues, and application crashes. PHP provides built-in functions to validate JSON strings efficiently.

Why Validate JSON?

• Prevent Errors: Catch malformed JSON before it causes runtime errors
• Security: Protect against malicious or malformed data inputs
• Data Integrity: Ensure data conforms to expected structure
• Better Debugging: Identify issues early in the data processing pipeline
• API Reliability: Validate external API responses before processing

Method 1: Using json_validate()

PHP 8.3 introduced the json_validate() function specifically designed for fast and efficient JSON validation. Unlike json_decode(), it does not parse the JSON or create PHP arrays/objects. Instead, it performs a lightweight structural check, making it ideal for high-performance validation.

Example
$jsonString = '{"name": "John", "age": 30}';

if (json_validate($jsonString)) {
echo "Valid JSON!";
} else {
echo "Invalid JSON!";
}

Why Use json_validate()?

• More Efficient: Uses significantly less memory than json_decode()
• Faster: Skips object/array construction
• Purpose-built: Specifically designed for validation use cases
• Ideal for Large Payloads: Works better when handling large API responses or config files

Method 2: Using json_decode() with Error Checking

Before PHP 8.3, the common way to validate JSON was using json_decode() and verifying errors with json_last_error().

Example
$jsonString = '{"name": "John", "age": 30}';

json_decode($jsonString);

if (json_last_error() === JSON_ERROR_NONE) {
echo "Valid JSON!";
} else {
echo "Invalid JSON: " . json_last_error_msg();
}

Method 3: Try/Catch with Exceptions (PHP 7.3+)

You can enable exceptions when decoding JSON by using the JSON_THROW_ON_ERROR flag. This helps with cleaner error handling in larger applications.
Example
try {
json_decode($jsonString, true, 512, JSON_THROW_ON_ERROR);
echo "Valid JSON!";
} catch (JsonException $e) {
echo "Invalid JSON: " . $e->getMessage();
}

Best Practices for JSON Validation

• Use json_validate() in PHP 8.3+ when you only need to validate (best performance).
• Use json_decode() when you need both validation and parsed data.
• Use exceptions for large projects to simplify debugging.
• Sanitize Input: Always validate user-provided or external API data.
• Log Errors: Helps track malformed data issues in production.

Or , you can try out online jsonformatters like jsonformatter