I have an idea (it might be a dumb one, I'm not sure yet :)) of building an API on top of some of my companys internal systems/applications. I feel like the API itself will only pull and show information from the other system/applications database/files, at least to begin with, and hopefully will not need its own database. As mentioned I imagine the API will initially be read-only (GET), but I might add other methods to it later.

My problem is that I am not too big on writing these kind of Web APIs (hopefully I'll learn a lot along the way) and I really don't know where to start. Has anybody here built something similar? Or do you know of any similar projects on github/bitbucket etc. that I can take a look at?

I will be grateful for any tips, pointers or feedback, good as bad. :)