I've been working on an applciation utilizing Google's App Engine. The first version of my application sent about 500 bytes of information along with each user POST request. The second version upped this to around 100 bytes and the App Engine server started giving the error: Requested URI too long: ... HTTP/1.1" 414 – This is the http error returned when a post request is longer than the server is configured to accept. After a little research I found this excellent article: http://www.openjs.com/articles/ajax_xmlhttp_using_post.php that solved my problem. The short version of the article is: Don’t send the post parameters as part of the url, send them using the XMLHTTP object’s send method once the object has been opened using only the address, (everything before the ?), of the original post url. So, the original code that looked like: var my_url = "/myhandler?longstring=" + ...