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

Annotations already provide readOnlyHint, idempotentHint, and destructiveHint. The description repeats the read-only nature ('Side effects: none (read-only)') but adds no new behavioral context such as reservation status, pagination, or relationship to purchase-number. It does not contradict the annotations.

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?

The description is two sentences and front-loads the core purpose. The second sentence about side effects is redundant with annotations, but it is brief and does not clutter the description. Overall it is concise and efficient.

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?

Given the output schema, full parameter descriptions, and annotations, the description is sufficient for an agent to call the tool correctly. It could have explicitly differentiated from list-numbers, but that is already a minor usage-guidance gap already reflected in that score.

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 schema documents all parameters. The description adds no meaning beyond naming 'country and area (calling) code', which is already captured by the parameter descriptions. No extra details about channel or contains behavior are offered.

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 states a specific action ('Search'), a specific resource ('purchasable fax numbers'), and a clear scope ('specific country and area (calling) code'). This distinguishes it from the sibling list-numbers (likely owned numbers) and purchase-number (the actual purchase).

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?

The description clearly implies the use case: finding numbers available for purchase in a specific location. It doesn't explicitly mention alternatives or exclusions, but the word 'purchasable' provides enough context for an agent to know when to choose this over other list tools.

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