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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is covered. The description adds genuinely new context beyond the structured fields: no sign-in is required, and the call is non-committal (no purchase). Return format details (fields, availability format) are still absent.

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 short sentences, front-loaded with the core action and scope, then usage, then the non-purchase boundary. Every sentence carries information; nothing is filler.

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 search tool with no output schema, the description covers purpose, scope, non-commitment, and the key returned attribute (monthly price). It is close to complete; only richer return-shape and alternative-tool guidance are 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 coverage is 75% and the schema itself documents country, currency, and number_type. The description only reiterates country/city and mentions the monthly price; it adds no syntax, enum, or default guidance for currency or number_type, so it does not compensate for the residual gap.

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+resource: finds available phone numbers for a country and optional city, and notes it returns the monthly price. It distinguishes itself from purchase-flavored siblings only implicitly, and never names quote_number or quote_port, so it stops short of full sibling differentiation.

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?

"Use this when a local number is needed" gives a clear use context, and "This does not purchase a number" draws a useful boundary. It does not, however, route the agent to the obvious alternatives (quote_number, prepare_order) for pricing or buying, leaving the when-not-to-use case implicit.

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