Rebuff AI

Rebuff is an open-source self-hardening prompt injection detection framework, originally created by Willem Pienaar. The project uses a multi-layered defense combining heuristics, a dedicated LLM, a known-attack database, and canary tokens to protect AI applications.

Rebuff became part of Protect AI in July 2023. Protect AI is a Seattle-based AI security company that was itself acquired by Palo Alto Networks in 2025. Rebuff is maintained as open source under Apache 2.0 alongside other ML security tools.