PromptShield sits between your users and your LLM, blocking prompt injection attacks before they reach the model. 4 layers of defense: 1. Input Classifier – detects malicious patterns 2. Context Sanitizer – strips injected instructions 3. Prompt Integrity Checker – validates structure 4. Output Monitor – catches successful injections Tunable aggression, API auth, rate limiting, audit logs, Python SDK, Docker. Benchmark tested. Built by a CS student from Nairobi, Kenya.