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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is covered. The description adds genuine context beyond that: the required 'fax:read' scope and the caveat that evidence is carrier-reported rather than legal proof of acceptance. It says nothing about how long evidence is retained or what a queued fax returns.

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?

Front-loads the status enumeration, then the evidence semantics, then the scope. Three dense sentences with little waste; the evidence caveat is longer than strictly needed but carries real meaning.

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 needn't be explained, and the description covers status meaning, evidence semantics, and auth scope. The only real gap is guidance on supplying a valid fax_id.

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?

The single parameter fax_id has 0% schema description coverage and the description never mentions it — no format, source, or where to obtain a fax id. With low coverage the description is expected to compensate and it does not.

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 the resource precisely ('the state of one fax and its attempts') and enumerates the possible statuses, so the agent knows exactly what comes back. It is clearly the single-fax counterpart to list_faxes, but it never names that sibling explicitly.

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?

'Once the fax is delivered or partial this is the one place for the carrier's delivery evidence' gives a concrete condition for selecting this tool over polling other endpoints. There are no explicit exclusions or named alternatives, so routing still requires some inference from sibling names.

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