json_decode Returns Null

Why This Happens

json_decode() returns null when the input is not valid JSON. Common issues include using single quotes instead of double quotes, trailing commas after the last element, unescaped control characters, or a UTF-8 BOM at the start of the string. Always check json_last_error() after decoding.

The Problem

$json = "{'name': 'Alice'}"; // Single quotes are not valid JSON
$data = json_decode($json, true);
echo $data['name']; // Error: $data is null

The Fix

$json = '{"name": "Alice"}';
$data = json_decode($json, true);
if (json_last_error() !== JSON_ERROR_NONE) {
    throw new RuntimeException('Invalid JSON: ' . json_last_error_msg());
}
echo $data['name'];

Step-by-Step Fix

1. 1

   Check the raw JSON

   Print the raw JSON string to see its actual content. Look for single quotes, trailing commas, unescaped characters, or BOM markers.

2. 2

   Validate with json_last_error

   Call json_last_error() and json_last_error_msg() after json_decode() to get a specific error description.

3. 3

   Fix the JSON source

   Correct the JSON syntax at its source. Use a JSON validator tool to find the exact location of the syntax error.