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

Annotations declare openWorldHint=true and idempotentHint=true, which the description does not contradict. However, the description adds no behavioral detail beyond the basic action—it does not state whether the original PDF is modified, whether a new file is returned, or any side effects like fetching from a URL. With annotations covering some traits, a score of 3 is appropriate.

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 a single sentence, front-loaded with the core action, and contains no extraneous words. It is efficient and easy to parse.

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?

The description is minimal and does not mention the critical requirement that a PDF must be supplied via source_url or file_base64. While the schema documents these parameters, the description could guide the agent on how to provide the input. The output schema exists, so return values are covered, but the input source requirement is a notable gap for a tool with optional parameters.

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?

The input schema has 100% parameter description coverage, so the baseline is 3. The description does not elaborate on parameters, such as the necessity of providing either source_url or file_base64. It adds no extra meaning beyond what the schema already provides.

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 clearly states the action: 'Add password protection (encryption) to a PDF.' It specifies a verb (Add), a resource (password protection), and a target (PDF), which distinguishes it from siblings like unlock_pdf (removing protection) and compress_pdf (compressing). The purpose is unambiguous.

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 implies usage when password protection is needed, but it does not explicitly mention alternatives or exclusions. An agent must infer that this tool is for encrypting a PDF, not for other PDF operations. There is no guidance on when not to use it or how it differs from unlock_pdf or other PDF tools, so the guidance is only implied.

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