Mcp.InjectionGuard
Roslyn-based prompt-injection defence gate for the MCP fleet: statically scans every [McpServerTool] method in the consumer repo and asserts that user-generated content (HTTP bodies, JSON from external APIs, tool output) is wrapped through UntrustedContent.Wrap / UntrustedContent.WrapJson before being returned. Methods can opt in via [ExternalContent] or out via [NotExternalContent]; in their absence a conservative name + return-type + invocation heuristic classifies tools. Per-method exemptions and heuristic overrides via injectionguard.json. Companion to the parallel Mcp.Auth.ResourceServer UntrustedContent helper.
Install
dotnet add package Mcp.InjectionGuard --version 0.1.0
Install-Package Mcp.InjectionGuard -Version 0.1.0
<PackageReference Include="Mcp.InjectionGuard" Version="0.1.0" />
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