Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

The annotations declare idempotentHint=true, but the description says 'The PDF must not be protected already.' After a successful call, a repeated identical call would fail because the PDF is now protected, which contradicts idempotency. Per the rubric, a description that contradicts annotations receives a score of 1.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is compact and well-structured: it states the core action first, then the encryption behavior, a precondition, cost, and return value. Every sentence contributes essential information with no redundancy or filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a simple two-parameter tool with no output schema, the description covers the input, a key precondition, the credit cost, and the nature of the return value (temporary download link with 15-minute validity). It is mostly complete, though it does not describe the error behavior if the PDF is already protected.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so both parameters are already documented in the input schema. The description adds no extra meaning about file format, password constraints, or parameter relationships beyond the schema, so the baseline score of 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific verb and resource: 'Add a password to a PDF' and 'Encrypts the PDF so it asks for the password when opened.' This clearly identifies the operation and distinguishes it from the sibling unprotect_pdf without opening the schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description gives a precondition ('The PDF must not be protected already') but provides no guidance on when to use this tool versus alternatives. It does not mention unprotect_pdf or any condition under which another sibling tool would be more appropriate, so an agent gets no routing help.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.