Most major Eaglercraft servers (like Aeon or Zentic) have active staff and anti-cheat systems. Using high-velocity fly hacks will result in an instant IP ban.
The Ultimate Guide to Eaglercraft Hacked Clients: Features, Risks, and Links Eaglercraft Hacked Client Links
Since you are running JavaScript in your browser, downloading "clients" from sketchy sources can lead to browser hijackers or credential theft. Stick to well-known community names. Most major Eaglercraft servers (like Aeon or Zentic)
Eaglercraft hacked clients are a powerful way to change how you play, but they should be used responsibly and primarily in single-player or "anarchy" server environments. Eaglercraft Hacked Client Links