My apologies for sending out this e-mail so late. As of r52190 [1], API maxlag errors (the kind of error you get when you set &maxlag=2 and the maximum slave lag is higher than two seconds) return a HTTP 503 status code rather than a 200, for consistency with index.php (which does the same thing). The text of the response has not changed: <api> <error code="maxlag" info="Waiting for 10.0.6.38: 1 seconds lagged" /> </api> To trigger a maxlag error, you can set &maxlag=-1 [2]. Be aware that some client libraries may treat the 503 return code differently, which is why this could be a breaking change. Roan Kattouw (Catrope) [1] http://www.mediawiki.org/wiki/Special:Code/MediaWiki/52190 [2] http://en.wikipedia.org/w/api.php?maxlag=-1&action=query