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

Annotations only declare that this is a mutating, non-destructive, confined operation; the description goes well beyond by disclosing auth requirements (signed URL, no API key), expiry windows (2-hour free / 24-hour keyed), rate limits (20/hour, 5 unused uploads), and server-side behavior (accepts any PDF, 415 only for non-PDF, returns a read report). The one gap is that the response's warning semantics are only gestured at rather than described in detail.

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?

It is front-loaded with purpose and return shape, then flows into the PUT protocol, then limits. Dense and mostly earning its length, but 'no auth needed — the URL is signed' and 'No API key or sign-in needed' restate the same fact, and the limits paragraph is packed into one long sentence.

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?

There is no output schema, yet the description supplies the return fields, the follow-up call, the out-of-band PUT contract, error conditions, and quota behavior — everything needed to drive a correct multi-step flow. Nothing essential for correct invocation is missing.

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?

With zero input parameters the baseline is 4; the description correctly conveys that no inputs are required and that authentication is optional rather than a parameter. It adds the relevant non-schema contract — that the real payload is sent out-of-band via PUT to put_url with Content-Type: application/pdf.

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 opens with a precise verb+resource ('Start a PDF upload') and immediately enumerates the return payload {upload_id, put_url, expires_at, max_bytes}, so the agent knows exactly what it gets back. It also names the downstream sibling create_order, distinguishing this step in the pipeline from the ordering step.

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 is explicit about when to call (you need an upload_id before create_order), how to follow up (HTTP PUT the bytes to put_url), and when to avoid calling (reuse an upload_id you already hold rather than creating extras). The alternative path — an API key via apply_enterprise to lift limits — is named with its concrete benefit (24-hour put_url).

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