Ranked in these QuestionsQuestion Ranking
Pro Automatic documentation and Haskell/JS query generation
servant-client for Haskell.
Con Route definitions are more verbose and complicated than other options
You are required to define a number of separate complicated types and their implementations which are usually spread out over a number of files. This makes it hard to figure out the API.
Con Route specifications and implementations are only connected by their position in a large type list
You actually have to count the index of the entry where you changed the specification, and then go and change the entry at the same index in the list of implementation methods. There is no other indication that the two are connected. This along with complex and verbose route definitions, makes it very hard to safely make changes to an API.
Con No built-in authorization handling
Currently, authorization must be handled through some other package (or custom code). Managing authorization directly within Servant, including OAuth and other tokens, is under development.