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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds useful context that each item carries its most recent code, but says nothing about pagination behavior, ordering, or what an empty result means. Since an output schema exists, the modest return-value note plus annotations is enough for a 3.

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 brief and front-loaded, and every word is readable, but the opening fragment "Rented SMS numbers." merely restates the title and earns nothing. It is more sparse than dense — the space saved by dropping that fragment could have documented the tab parameter.

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?

With an output schema present, the description needn't explain return values, and annotations cover safety, so the remaining burden is small. However, a three-parameter listing tool whose active/archived switch and pagination are entirely undocumented leaves the agent guessing at defaults and page size, so it is only minimally complete.

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 33%: only last_id is documented in the schema, while tab (enum active/archived) and per_page have no explanation anywhere, including the description. The description does not compensate for the gap — no default tab, no page size guidance — but with an output schema and a self-explanatory enum, the omission is not fatal.

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?

"List the current account's rented numbers with their most recent code" gives a specific verb, resource, and scope, and the mention of the latest code hints at how it differs from code-fetching siblings. It never names or explicitly contrasts with the nearby alternatives (sms_rental_get_codes, sms_activation_list_numbers), so the differentiation is only implicit.

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?

There is no guidance on when to use this tool versus sms_rental_get_codes or sms_activation_list_numbers, and nothing tells the agent when the archived tab is appropriate versus active. The only hint of usage is the phrase "current account's," which is scope, not guidance.

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