# ToFu

When a large language model calls an external tool, the orchestration layer checks that the call is well formed, not that its arguments are safe. ToFu turns the argument semantics already documented in tool metadata into executable security checks, then generates fuzzing inputs and oracles from them, confirming 253 bugs across 343 tools in 118 of 273 runnable MCP servers, most of which returned normally.

When a large language model calls an external tool, the orchestration layer checks that the call is well formed, not that its arguments are safe. ToFu turns the argument semantics already documented in tool metadata into executable security checks, then generates fuzzing inputs and oracles from them, confirming 253 bugs across 343 tools in 118 of 273 runnable MCP servers, most of which returned normally.