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

Annotations already establish this is a safe read (readOnlyHint=true) with a closed data scope (openWorldHint=false). The description adds genuinely useful behavioral context: ended rentals are excluded by default, which materially affects results. It stops short of describing ordering, pagination, or empty-result 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 short sentences with no filler; the core listing behavior and the important default-filter caveat are both front-loaded. Every clause earns its place.

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 single-optional-parameter read tool with annotations covering safety and no output schema, the description gives enough to call it correctly and predicts the shape of results via country/period/end date. Minor gaps remain around result ordering, pagination, and result size limits.

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 only parameter already documents 'Also list rentals that have ended (default false).' The description's 'Ended rentals are left out unless includeEnded is true' conveys the same semantics in context but adds no new detail, so the baseline 3 applies.

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 specific verb and resource ('List the account's rented numbers') and even names the fields returned (country, period, end date), which distinguishes it from mutation siblings like cancel_rental or rent_number. It does not explicitly differentiate from the read-side siblings such as get_inventory or read_rental_sms, leaving the agent to infer the boundary.

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?

Usage is implied by the includeEnded condition: the default is active rentals, and setting the flag broadens it. However, the description never states when an agent should choose this over sibling tools (e.g., read_rental_sms or get_inventory), and no prerequisites or exclusions are given.

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