Is parsing JSON faster than parsing XML

Firstly, I'd like to say thanks to everyone who's answered my question. I REALLY appreciate all of your responses.

In regards to this question, I've conducted some further research by running some benchmarks. The parsing happens in the browser. IE 8 is the only browser that doesn't have a native JSON parser. The XML is the same data as the JSON version.

Chrome (version 8.0.552.224), JSON: 92ms, XML: 90ms

Firefox (version 3.6.13), JSON: 65ms, XML: 129ms

IE (version 8.0.6001.18702), JSON: 172ms, XML: 125ms

Interestingly, Chrome seems to have almost the same speed. Please note, this is parsing a lot of data. With little snippets of data, this isn't probably such a big deal.

Benchmarks have been done. Here's one. The difference in some of the earlier browsers appeared to be an entire order of magnitude (on the order of 10s of milliseconds instead of 100s of ms), but not massive. Part of this is in server response time - XML is bulkier as a data format. Part of it is parsing time - JSON lets you send JavaScript objects, while XML requires parsing a document.

You could consider adding to your public API a method to return JSON instead of modifying existing functions if it becomes and issue, unless you don't want to expose the JSON.

See also the SO question When to prefer JSON over XML?

JSON should be faster since it's JS Object Notation, which means it can be recognized natively by JavaScript. In PHP on the GET side of things, I will often do something like this:

<script type="text/javascript">
    var data = <?php json_encode($data)?>;
</script>

For more information on this, see here:

Why is Everyone Choosing JSON Over XML for jQuery?

Also...what "extra effort" do you really have to put into "generating" JSON? Surely you can't be saying that you'll be manually building the JSON string? Almost every modern server-side language has libraries that convert native variables into JSON strings. For example, PHP's core json_encode function converts an associative array like this:

$data = array('test'=>'val', 'foo'=>'bar');

into

{"test": "val", "foo": "bar"}

Which is simply a JavaScript object (since there are no associative arrays (strictly speaking) in JS).