If you're building AI agents that process user input, RAG documents, or tool outputs — you need prompt injection detection. This tutorial shows you how to add it in under 5 minutes with a free API. Why prompt injection detection matters Large language models can't reliably distinguish between legitimate instructions and injected ones. When your agent processes untrusted input — a user message, a document from RAG, an API response, a code file — an attacker can embed instructions that manipulate what the agent does. This is the same class of attack that Johns Hopkins researchers used to hijack Claude Code, Gemini CLI, and GitHub Copilot. The fix isn't better prompting. It's an external security boundary that classifies input before it reaches the model. Step 1: Get an API key Sign up at agentshield.pro/signup — just your email, no credit card. You'll get a key instantly. The free tier gives you 100 requests per day.…