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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds one real behavioral fact — the area_code default of 415 — but says nothing about result volume, limits, or why openWorldHint=false matters.

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?

One short sentence, front-loaded with the verb and resource, with the useful default in parentheses. Nothing wasted.

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 no output schema and no param descriptions, the description should say what a result looks like (numbers only, or with pricing/capabilities) and whether results are capped. For a simple read-only lookup the essentials are present, but these gaps remain.

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 0%, so the description carries the burden, and it does supply the meaning of area_code plus its default value of 415, which the schema does not. It stops short of specifying format or validation (3-digit NANP, US-only scope).

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 ('Search') and a specific resource ('purchasable numbers'), scoped by area code. This implicitly separates it from list_numbers (owned inventory) and purchase_number / bulk_purchase_numbers, but no sibling is named explicitly.

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 word 'purchasable' implies the pre-purchase lookup flow, but the description never says to call it before purchase_number or bulk_purchase_numbers, nor does it state any exclusions. Usage is inferable but not stated.

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