Running back and forth while working out in the prison gym is cited as the fastest "zero-risk" way to reach Level 100, especially when done in low-population servers.
If you prefer to avoid the risks of script-based farming (such as account bans), these are the most effective manual strategies:
Using automated scripts or "exploits" is against the Roblox Terms of Service . Developers of Mad City frequently patch these glitches and may issue permanent bans to accounts caught using "Auto-Farm" GUIs.
Automatically kills or arrests nearby NPCs and players, racking up bounty and XP rewards instantly. Top Legitimate XP Grinding Methods