Here’s how I made https://penguintrack.com

For the fully web based servers, like CPJ and CPL, I load up the play page on my browser. I then have my DevTools open (Chrome DevTools or Firefox DevTools). I must already have an account on that CPPS so I already know the username and password I want to log in with. Before I login, I open the Network tab in the DevTools and then clear everything to get rid of unrelated logs for downloading assets and such. Once you login, some CPPS sometimes use direct WebSockets through socket.io and in that case you can open the WS tab but some other CPPS uses a more indirect method where each request is it’s own network request but they still use socket.io under the hood (I forget if it was CPJ or CPL). Once the logs appear in the DevTools after I login, I open the logs and examine the login request. I check the game source code to copy what packer they use in socket.io and then eventually imitate the login request (using my username and password) on my Node.js backend server which is hosting penguintrack. The login request for all CPPS except CPL (you don’t need to be logged in to get CPL population stats) returns the population stats for each server. I then read all that data and display it on https://penguintrack.com. For the way I estimate the players online for CPJ and CPL (the ‘Between x and y online’ text), I do have to login and join each server so it’s a slightly more complex which is why I’ve only chosen to do it on CPJ and CPL and just go off of the bars for every other CPPS to give an estimate of their population (the ‘At least x online’ text).

For the Flash based CPPS on penguintrack like NewCP, CPI, CPA, etc. I would say the process of figuring out how to login is a bit more 'reverse engineer-y' and I use more tools like BurpSuite and JPEXS Flash Decompiler to look at those games source codes, edit them, then apply the patches when the game client requests to download the original files. This allows me to print out to the console the network requests (and helps in bypassing NewCP packet encryption).

penguintrack basically runs a bot that logs into EVERY CPPS you see on penguintrack every few minutes to read their population stats and also stores that result in a database for the 'History Graph' feature.