Tool · curated 25 Jul 2026

GitHub - StackOneHQ/defender: Open source prompt injection protection for Agents calling tools (via MCP, CLI or direct function calling). Detect and defend against prompt injection attacks. 22MB, CPU-only, < 10ms latency.

First reported today github.com

Coverage timeline

Single-source analysis — first reported, latest, and curated coincide.

Why it matters

Defender gives builders of tool-calling AI agents a lightweight, self-hostable guardrail to catch prompt injection at the tool/MCP boundary where indirect injection commonly enters.

Defender by StackOneHQ is an open-source tool that detects and defends against prompt injection attacks targeting AI agents that call tools via MCP, CLI, or direct function calling. It is described as a 22MB, CPU-only classifier with sub-10ms latency and covers both direct and indirect prompt injection.