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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds real context beyond that: the API-key auth requirement for fax_id and the visibility scoping ('only your own faxes are visible'), which an agent needs to avoid surprising behavior.

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?

Two tight sentences: the purpose first, then the parameter routing and auth caveat. No filler, and the operationally important constraint is front-loaded.

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 compact two-parameter read tool with no output schema, the description covers purpose, parameter routing, and the auth/visibility constraint. It omits edge-case behavior (pending faxes, missing/expired token, mutual exclusivity of the two params), leaving slight room for ambiguity.

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 description coverage is 100%, so the baseline is 3. The description nonetheless adds value beyond the schema by tying token/fax_id to order type routing and surfacing the auth/visibility constraint. It does not state whether the two parameters are mutually exclusive, which is a minor gap.

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+resource ('Check the delivery status of a fax'), which is clear and unambiguous. It does not explicitly contrast with close siblings like list_fax_history or send_fax, but the resource is distinctive enough that an agent can separate it without opening the 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?

Routes the agent between the two parameters by order type: 'token for pay-per-fax orders, fax_id for subscription orders.' That is genuine selection guidance, not just a restatement. It stops short of naming alternatives or stating when the tool should not be used.

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