2011/3/23 richardcavell@mail.com:
URL
This is fairly high, but I'm not sure just how high. If you're concerned your query strings will get cut off, use POST instead of GET.
page title
255 bytes (MediaWiki-enforced limit). This does NOT include the namespace prefix
page content (wikitext and HTML versions)
The wikitext limit is configurable. On Wikipedia this is 2000 KB. There is no limit on the HTML size.
HTTP response from server
No limit.
edit token login token
Always the same length, don't recall the exact number offhand. We may make it longer without announcement if needed, though.
username
255 bytes, as usernames are also titles.
Roan Kattouw (Catrope)