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

Annotations already declare readOnly/idempotent/non-destructive, and the description reinforces this ("It changes nothing", "a report on one PDF (nothing changed)") while adding context annotations cannot express: exact report contents, 422 on encrypted input, 503 and no-charge behavior past ~78 s, typical <2 s latency, per-IP free tier pricing, and a prompt-injection warning about returned page text. This is unusually complete behavioral disclosure for a read-only tool.

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?

Everything in the paragraph earns its place — limits, error codes, timing, and the untrusted-data warning — and the sibling differentiation is stated early. However, the first clause is pricing ("Price: USD 0.005; Free: 3 pdfpeek calls...") rather than the tool's action, and the content is delivered as one dense run-on, so the read is slightly front-loaded with the wrong thing.

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 read-only inspector with an output schema and full annotation coverage, the description supplies everything an agent still needs: latency, page cap, error semantics, charging behavior, and a safety note about returned text. The minor dangling reference to `text_analysis` is the only soft spot.

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% and both parameters already document size limits and the url/pdf_base64 either-or, so the description does not need to restate them. It adds only indirect input constraints (encrypted files rejected, 2,000-page cap), which is baseline-appropriate but not compensating value beyond the schema.

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?

States a specific verb and resource ("Inspect a PDF: page sizes, text layer or scan, forms, attachments, JavaScript, bookmarks") and explicitly contrasts with the sibling pdf_metadata for title/author/date reading. An agent can distinguish it from pdf_extract, pdf_form_fields and pdf_metadata without opening any 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?

Gives an explicit alternative ("for title, author and dates, or to edit them, use pdf_metadata") plus a prerequisite for the encrypted case ("Encrypted input is a 422 (unlock it first)"), routing to pdf_unlock. It also states the operational envelope (2,000 pages, 20 s text_analysis) that determines when the call is appropriate.

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