<pre><code>  $a = '{ "tag": "&lt;b&gt;&lt;/b&gt;" }';
  echo json_encode( json_decode($a) );
</code></pre>

<p>This outputs:</p>

<pre><code>{"tag":"&lt;b&gt;&lt;\/b&gt;"}
</code></pre>

<p>when you would think it would output exactly the input.  For some reason json_encode adds an extra slash.</p>

Because it's part of the JSON standard
http://json.org/
char
```
```
any-Unicode-character-
    except-"-or-\-or-
    control-character
\"
\\
\/ <---- see here?
\b
\f
\n
\r
\t
\u four-hex-digits
```
```