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Dev.to
7/23/2026
The original title is: "L1.9: A prompt injection defense layer for MCP-based AI agents with 28 detection rules"

The original title is: "L1.9: A prompt injection defense layer for MCP-based AI agents with 28 detection rules"

Original: L1.9: I built a prompt injection firewall for AI agents (28 detection rules)

Short summary

L1.9 is a prompt injection defense layer that scans MCP server tool descriptions, system prompts, and skill metadata against 28 detection rules before an agent installs a skill. Rules cover override commands, role-change attempts, data exfiltration instructions, and conditional activation patterns. Findings are scored by severity (critical/high/medium) and quarantined when thresholds are exceeded. The tool is part of a 10-layer security stack from AliceLabs LLC.

  • •28 detection rules scan MCP tool descriptions, system prompts, and skill metadata for prompt injection
  • •Findings scored by severity: critical quarantines immediately, 2+ high findings recommend quarantine
  • •Part of a broader 10-layer security stack; live on marketnow.site with GitHub source

Generated with AI, which can make mistakes.

#ai-tools#ai-agents#open-source
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