How to counter Akali
Let us take a look on how to beat Akali. We will look at champions who are strong against Akali and who are weak against Akali. Use win rate, gold difference and creep score difference at minute 10 to find the best 
Mid champion who counters Akali. You can already win in champion select with the right counters for Akali. If you want to know how to counter Akali then you need to take into account the best picks vs Akali and the worst picks vs Akali. This Akali counter data is based on matches played by Pros on patch 15.14 and previous ones. It is important to see whether Pros counter picked Akali or whether they played as Akali.
Champions used by Pros to counter pick Akali
Looking at the matches from Pros (see table Pros counter picked Akali) we can see that they picked 
Orianna most often to counter pick Akali. The matchup Orianna vs Akali occured 32 times. Akali has 19 wins and 13 losses in this matchup. Learn how to counter pick Orianna to get another perspective on the data.
Lane outcome for Akali
When looking at Akali counters you will notice that win rates alone are not conclusional. Therefore we provide an overview (see table Lane Outcome) where you can see the lane outcome of Pros who played Akali. The lane outcome of Akali consists of three outcomes: Win, Loss or Draw. Let's take a look of Akali lane and match outcome for specific matchups. Considering the lane outcome and the match outcome of a specific matchup, might enable you to find the right counter for Akali.
Conclusion
Analyze the available data and learn how to beat Akali. To master Akali take also a look on Akali builds and runes for Akali. Good luck, Summoner!