As far as I'm aware, 343 doesn't keep a page detailing what maps and game types are available in each playlist. It's very common for players to ask on the forums and Reddit what maps and game types are in a given playlist, and I've only been able to tell them based on my own match history. The problem is that I don't play every playlist, so I can't help answer the question "what maps are in Snipers?"
The idea here is that we'll periodically pull the last 100 games from the API and be able to generate a list of maps/game types. We use multiple different players in order to have games from people who play each list.
We also track the number of games of each map/mode, so that we can report on the relative weighting within a playlist. I'm not sure how accurate this is, but it should converge after enough games are collected (more than a hundred).
We are scraping the following players. To add your name to the list, just ask!
If you have any questions or complaints, feel free to yell at me on twitter.