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

Annotations already flag a non-read-only mutation, but the description adds valuable details beyond them: the credit cost, the 15-minute validity of the returned link, and the instruction to always include the link in the reply. This is useful behavioral context not present in structured fields.

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?

Three short sentences with no filler: purpose, constraint, cost, and output link handling. The most critical information (what it does) is front-loaded, and every sentence carries functional weight.

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 tool with two simple parameters, the description covers the precondition, cost, output format (temporary link), and a direct instruction for the agent. Nothing needed for correct invocation is missing, and the lack of an output schema is compensated by the explicit link description.

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 coverage is 100% for both parameters (file as base64 PDF, password as required). The description adds a meaningful constraint on the file parameter ('must not be protected already') that is not in the schema, enhancing understanding. It doesn't repeat schema text, so it earns above baseline.

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 uses a specific verb ('Add a password') and resource ('PDF'), then explains the encryption effect ('asks for the password when opened'). This clearly distinguishes it from the sibling unprotect_pdf and other PDF tools, leaving no ambiguity about the operation.

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?

It gives a clear precondition ('The PDF must not be protected already') and states the credit cost, which helps an agent decide when to invoke it. However, it does not explicitly mention the alternative unprotect_pdf or provide when-not-to-use guidance, so it stops short of full routing.

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