What is a Tool Description Mismatch?
A discrepancy between what a tool's metadata claims it does and what the underlying code actually executes, found in approximately 13% of MCP servers and enabling undocumented privileged operations.
WHY IT MATTERS
An MCP tool's description is what the agent sees when deciding whether and how to use it. If the description says 'read user profile' but the code actually modifies user settings, the agent makes decisions based on false information.
Mismatches can be accidental (sloppy documentation) or malicious (intentional deception). Either way, agents relying on descriptions alone are vulnerable. Independent classification based on code analysis and behavioural testing catches what descriptions miss.
HOW POLICYLAYER USES THIS
PolicyLayer's crawler analyses tool source code via static analysis, comparing what tools claim to do against patterns in the actual implementation.