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

Annotations already indicate the tool is not read-only, is idempotent, and is not destructive. The description adds a small behavioral note about maintaining readability, but it does not explain whether the original file is preserved, whether a new compressed file is returned, or how compression affects quality beyond the schema's quality parameter.

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, direct sentence that front-loads the action and outcome. There is no wasted wording, and every phrase contributes to understanding the tool's purpose.

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 a complete input schema, an output schema, and annotations covering safety and idempotency, the description is largely sufficient. It clearly communicates the core function, though it could slightly improve by mentioning whether the original file is modified or a new compressed file is produced.

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 the input schema fully documents both the 'file' object and the 'quality' parameter. The description itself does not add parameter-level detail beyond what the schema already provides, 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 uses the specific verb 'compress' and names the resource 'PDF', clearly distinguishing this tool from the sibling tools like extract_pages, merge_pdfs, and rotate_pdf. It also states the intended outcome: reducing file size while preserving readability.

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 the tool should be used when a PDF's file size needs to be reduced while keeping it readable, but it does not explicitly state when not to use it or name alternatives. Since all sibling tools perform different PDF operations, the usage context is reasonably clear but not fully explicit.

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