AgentShield is a prompt injection classifier that sits between untrusted input and your AI agent. One API call classifies any text — user messages, RAG documents, tool outputs — and returns a verdict before it reaches the model. Think of it as a WAF for LLMs. Why we built it: Johns Hopkins researchers hijacked Claude Code, Gemini CLI, and GitHub Copilot through prompt injection. The three biggest AI companies couldn't stop it. We built an external security layer that does.