# json_decode() returns null / JSON_ERROR_SYNTAX: Syntax error

**Code:** `json_decode null` · **Category:** PHP · **Seen on:** PHP

The string passed to json_decode isn’t valid JSON, so PHP returns null.

## Meaning

json_decode fails silently unless you check json_last_error() or use JSON_THROW_ON_ERROR. Common inputs that break: BOM at the start, HTML error pages, single quotes, trailing commas, or a body you never read.

## Common causes

- Response is HTML or empty, not JSON
- UTF-8 BOM / invalid UTF-8
- Single quotes or trailing commas
- Reading $_POST instead of php://input

## Quick fix

1. Use `json_decode($s, true, 512, JSON_THROW_ON_ERROR)`
2. Log the raw string when decoding fails
3. Read raw bodies with `file_get_contents('php://input')`

## Detailed fix by platform

### PHP

1. `try { $data = json_decode($raw, true, 512, JSON_THROW_ON_ERROR); } catch (JsonException $e) { error_log($e->getMessage() . ': ' . substr($raw, 0, 200)); }`

## How to diagnose

1. **Raw** — What does the string look like?
2. **Error** — json_last_error_msg()

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Source: [WhatIsMyError](https://whatismyerror.com/errors/php/json-decode-syntax-error)