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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and openWorld, so the safety profile is covered. The description adds that no wallet/payment is required and no arguments are taken, but it doesn't disclose whether the returned sample is fixed/canned data, how representative it is, or any rate limiting on preview calls.

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?

A single sentence, front-loaded with the [FREE] tag and the key purpose. It is appropriately sized for a zero-argument preview tool, with only mild redundancy between the parenthetical title and the sentence body.

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 zero-arg, no-output-schema preview tool with full annotations, the description covers purpose, cost model, and input expectation adequately. The only minor gap is not clarifying that the returned sample is static and unrelated to any real document.

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?

Zero parameters with 100% schema coverage gives a baseline of 4. The description reinforces this by confirming 'no arguments needed', which matches the empty schema and prevents an agent from hunting for inputs.

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 resource and scope: it returns a free sample response for pdf_extract so the caller can inspect the response shape. It clearly distinguishes itself from the paid sibling pdf_extract by noting the free/no-payment nature, though the framing is closer to marketing copy than a crisp verb+resource statement.

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 usage condition well: use this to preview the response shape before paying 0.04 USDC for the real pdf_extract. It doesn't name pdf_extract as the explicit follow-up alternative in a 'use X instead' form, but the pricing reference makes the when-to-use case obvious.

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