https://tools.wmflabs.org/glamtools/treeviews/?q=%7B%22lang%22%3A%22it%22%2C%22pagepile%22%3A%22492%22%2C%22rows%22%3A%5B%5D%7D will make requests such as https://wikimedia.org/api/rest_v1/metrics/pageviews/per-article/it.wikipedia/all-access/user/Antonio_De_Gennaro/daily/20160401/20160431 At the third attempt, I got 408 pages with views in April, but that error message "end timestamp is invalid, must be a valid date in YYYYMMDD format" is unhelpful. The request shouldn't be made invalid by a numerical range which is too wide (i.e. which includes non-existing days) .
Oh I see, if the request is to not validate dates, then I would personally decline that. We validate parameters to make sure the user is asking for what they want. If they're typing these numbers by hand they might make a typo that causes them to return way too much data. We'll be adding limits to how much data can be retrieved at any one time, but still, it might be more data than they need by far. That's what validation is for, to catch simple mistakes. I'm not seeing the argument here, but I'll leave it open in case you have examples of similar implementations that ignore parameter validation.