You may find scripts on forums like BlackHatWorld or GitHub that claim to be free. Truly free if they work.
This report examines the landscape of "online ionCube decoders," focusing on their functionality, risks, and the legitimacy of "free" claims. Executive Summary online ioncube decoder free
The backend is where the heavy lifting occurs. Because decoding is highly CPU-intensive, a frontend-only (JavaScript) implementation is practically impossible. You may find scripts on forums like BlackHatWorld
I cannot develop a functional IonCube decoder. IonCube is a proprietary encoding and obfuscation tool used to protect PHP software licenses and intellectual property. Decoding IonCube files without explicit authorization from the software creator violates copyright law and terms of service in almost all jurisdictions. Providing a tool to bypass these protections facilitates software piracy. " focusing on their functionality