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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuinely useful context beyond that: it discloses the returned fields, the 'had numbers at the last snapshot' freshness caveat, and the two-step workflow with get_area_pricing. It does not mention pagination behaviour, though limit/offset in the schema largely cover that.

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?

Three sentences, zero filler, and the search scope is front-loaded before the return summary and the sibling routing. Every sentence carries distinct information: what it searches, what it returns, where to go next.

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 read-only, idempotent search with a full input schema and an output schema, the description covers the remaining gaps: what the results contain, the snapshot-freshness caveat, and the handoff to get_area_pricing. Nothing an agent needs in order to call this correctly is missing.

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 all five parameters are already documented, including the country pattern, number_type enum and query semantics. The description's 'such as London or 4420' gives a concrete illustration of the query parameter but adds little beyond what the schema already states, so the baseline 3 is appropriate.

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 names a specific verb and resource ('Search the number areas') and enumerates the searchable dimensions (country, number type, text) plus the covered range kinds. It also names the sibling get_area_pricing as the follow-up tool, so an agent can distinguish it from get_calling_rate and list_countries without opening schemas.

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?

It clearly routes the agent onward ('Use get_area_pricing with an id for the full details'), implying this is a summary/discovery call rather than a pricing-detail call. There is no explicit statement of when NOT to use it or which of the remaining siblings (get_calling_rate, get_forwarding_rate) to pick instead, so it stops short of full when/when-not coverage.

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