How to Write JSON File in PHP: Simple Guide

To write a JSON file in PHP, use json_encode() to convert your data to JSON format, then save it with file_put_contents(). This creates or overwrites the file with the JSON string.

Syntax

Use json_encode() to convert PHP arrays or objects into a JSON string. Then use file_put_contents() to write that string to a file.

• json_encode($data): Converts PHP data to JSON format.
• file_put_contents($filename, $jsonString): Writes the JSON string to the file.

php

<?php
$jsonString = json_encode($data);
file_put_contents('filename.json', $jsonString);
?>

Example

This example shows how to create an array, convert it to JSON, and save it to a file named data.json.

php

<?php
// Sample data array
$data = [
    'name' => 'Alice',
    'age' => 30,
    'city' => 'Wonderland'
];

// Convert array to JSON string
$jsonString = json_encode($data, JSON_PRETTY_PRINT);

// Write JSON string to file
file_put_contents('data.json', $jsonString);

// Output success message
echo "JSON file created successfully.";
?>

Output

JSON file created successfully.

Common Pitfalls

Common mistakes when writing JSON files in PHP include:

• Not checking if json_encode() returns false due to invalid data.
• Forgetting to handle file write errors from file_put_contents().
• Not using JSON_PRETTY_PRINT for readable JSON output.
• Writing to a file without proper permissions.

Always check for errors and ensure your PHP script has permission to write files.

php

<?php
// Wrong way: ignoring errors
$jsonString = json_encode($data);
file_put_contents('data.json', $jsonString);

// Right way: check for errors
$jsonString = json_encode($data);
if ($jsonString === false) {
    echo "JSON encoding error: " . json_last_error_msg();
    exit;
}
if (file_put_contents('data.json', $jsonString) === false) {
    echo "Failed to write to file.";
    exit;
}
?>

Quick Reference

Here is a quick summary of the main functions used:

Function	Purpose
json_encode($data, JSON_PRETTY_PRINT)	Convert PHP data to JSON string with readable format
file_put_contents($filename, $jsonString)	Write JSON string to a file
json_last_error_msg()	Get last JSON error message if encoding fails

Key Takeaways

Use json_encode() to convert PHP data to JSON format before writing.

Write JSON string to a file with file_put_contents().

Check for errors from json_encode() and file_put_contents() to avoid silent failures.

Use JSON_PRETTY_PRINT for readable JSON files.

Ensure your PHP script has permission to write to the target file.