PHP json_decode returns null: Syntax error and other causes

What the error means

json_decode returns null when decoding fails, and also when the JSON text is literally null. Without flags it does not say why. Pass JSON_THROW_ON_ERROR (PHP 7.3 and later) to get a JsonException, or call json_last_error_msg() right after the call. Syntax error covers most malformed input: a UTF-8 byte-order mark, single quotes, trailing commas, comments, invalid escapes, an empty string or HTML printed before the JSON. Invalid UTF-8 and control characters have their own messages. PHP does not report where the error is.

Exact messages by runtime

Messages depend on the input and runtime version. Node and Python rows were reproduced locally. Other rows cite official documentation or source. Rows marked as fragments or templates preserve the source wording and are not complete exception transcripts. Browsers and libraries may append location details.

Causes you can reproduce

<?php
var_dump(json_decode("{'id': 1}")); // NULL
echo json_last_error_msg();         // Syntax error

<?php
$json = "\xEF\xBB\xBF" . '{"id": 1}'; // as read from a file saved with a BOM
var_dump(json_decode($json)); // NULL
echo json_last_error_msg();   // Syntax error

<?php
$json = "{\"name\": \"Ren\xE9\"}"; // é encoded as Windows-1252
var_dump(json_decode($json)); // NULL
echo json_last_error_msg();   // Malformed UTF-8 characters, possibly incorrectly encoded

How to fix it

1. Decode with JSON_THROW_ON_ERROR, or check json_last_error() immediately after json_decode. The next json_encode or json_decode call replaces the stored error.
2. Inspect the first bytes with bin2hex(substr($json, 0, 16)). efbbbf is a byte-order mark, and 3c is <, the start of HTML or a PHP warning.
3. Fix syntax errors where the JSON is produced. Strip a byte-order mark only where you read the file, and convert legacy encodings to UTF-8 before decoding.
4. With exceptions enabled, a null result means the JSON text was null. Without them, compare json_last_error() with JSON_ERROR_NONE.

<?php
try {
    $data = json_decode($json, true, 512, JSON_THROW_ON_ERROR);
} catch (JsonException $e) {
    error_log('Invalid JSON: ' . $e->getMessage() . ' (code ' . $e->getCode() . ')');
    throw $e;
}

<?php
$json = file_get_contents('data.json');
if (str_starts_with($json, "\xEF\xBB\xBF")) {
    $json = substr($json, 3);
}
$data = json_decode($json, true, 512, JSON_THROW_ON_ERROR);

<?php
$json = mb_convert_encoding($legacy, 'UTF-8', 'Windows-1252');
$data = json_decode($json, true, 512, JSON_THROW_ON_ERROR);

Find the exact position with Tool Kumar

1. Copy the exact input text, including its original whitespace. For HTTP failures, copy the raw response body.
2. Open the Tool Kumar JSON validator and paste the text. The document stays in your browser.
3. Read the line and column in the error or fixable-issue banner. For an invalid document, select Go to error to move the caret to that location.
4. Inspect the preceding token as well as the marked character. A parser marks where it discovered the problem; the missing quote, separator or value can start earlier.

Python character offsets are zero-based, while its displayed lines and columns are one-based. V8 string positions count UTF-16 code units; Go offsets count bytes read. Unicode text can make these offsets differ. Use the original text and its line/column context rather than copying an offset between runtimes.

Tool Kumar can classify some input as fixable loose JSON. Review a proposed change before using the JSON repair tool, then validate the result against your API contract. For empty input, inspect the producer or response because there is no character to select.

Frequently asked questions

Related errors and tools

• JSON.parse: unexpected character at line 1 column 1 of the JSON data
• Expecting property name enclosed in double quotes
• JSON trailing comma errors in objects and arrays
• Bad control character in string literal in JSON
• Bad escaped character in JSON / Invalid \escape
• All JSON error guides
• JSON syntax reference
• Generate PHP classes from valid JSON

Standards and diagnostic sources

RFC 8259 and ECMA-404 define JSON syntax. Diagnostic wording belongs to the parser. The table links each cited message to its source.

• PHP manual: json_decode
• PHP manual: json_last_error_msg