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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuinely non-obvious behavior on top: the returned artifact is a PDF link that expires after a few minutes and must be handed to the person immediately, and undelivered faxes produce a reasoned refusal rather than a document. That expiration and failure path are the kind of detail annotations cannot express.

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 short and front-loads the resource, but several sentences are verbless fragments ('Answers a link that reads it, as a PDF, for a few minutes') that cost the reader a pass or two to decode. The time-limit fact is buried mid-clause when it is the most operationally important detail.

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?

An output schema exists, so return structure need not be spelled out, and the description still covers the link's short lifetime, the refusal case, and the delivered-only precondition. Only the lack of sibling disambiguation keeps it from being fully complete for a one-parameter read tool.

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 the single fax_id is already documented in the schema as 'as send_fax gave it'. The description adds nothing about the identifier's source or format, so baseline 3 applies — the schema does all the work here.

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 names a specific resource — the delivery confirmation for a fax the person sent — and even enumerates its contents (who received how many pages, from whom, when). That is enough to separate it from get_fax or send_fax, though it never explicitly contrasts with those siblings and the phrasing ('one page that says...') is roundabout.

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 implies usage through 'give the person the link' and states the tool is refused for an undelivered fax, which is a real precondition. However, there is no explicit statement of when to reach for this versus get_fax or send_fax_link, so the routing decision is left partly to inference.

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