Ever since Pokémon Go has been launched, Niantic has made it clear that the use of bots and trackers is a clear violation of the Terms of Service of the game. However, it would still be upon the player's discretion whether he'll be using some third party apps that this article does not promote. While having PokéCoins mean that a player has to take over a gym and hold it for a long time, which goes without saying that scouting for gyms, is necessary.
Pokémon Go Gym Tracker
According to Mic, GymHuntr is a website that shows a player where the nearby gyms are, who controls them, what kinds of Pokémon are there and who owns those Pokémon. However, the website emphasizes that it would only be able to tell the player these information based on the location that he puts in. So, if a player is really determined to take some gyms, some game enthusiasts say that it's a great site to check in order to avoid wasting of time.
Furthermore, as per Droid Report, the person behind GymHuntr is reportedly the same person who's been responsible for PokéHuntr. It was found that GymHuntr also has the ability to give an advanced tip on how to handle the logistics of one's planned attack. On the other hand, PokéHuntr is apparently a tempting aid for Pokémon Go players, which is still working to date despite Niantic's tightened Pokémon Go security features for third party apps.
Meanwhile, GymHuntr is allegedly a great tool for hitting multiple gyms quickly that hasn't been designed to help players keep them. Unfortunately, it was found that there's also a chance for Niantic to take action against GymHuntr itself, like it did with Pokévision last summer. Finally, as an unwritten rule, players are advised that if an app or website offers something that sounds too good to be true, it probably is.