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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds useful context beyond that: this is a per-area detail lookup that surfaces pricing, compliance documents, and a purchase link, which tells the agent it is an informational enrichment call rather than an action.

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?

A single sentence that front-loads the action and id source, then lists returned data. It is a long run-on but every clause is substantive and none is filler, so it stays within a reasonable size.

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 one-parameter read tool with a full output schema and complete annotations, this covers purpose, id provenance, and the shape of the payload. The only gap is the absence of sibling differentiation against get_calling_rate/get_forwarding_rate, which an agent comparing rate tools would find useful.

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 schema description already states 'Public area id from search_areas' with a format example. The description's '(from search_areas)' merely restates that, adding no new syntax, format, or constraint detail. Baseline 3 is correct when the schema carries the parameter documentation.

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 ('Get one number area by its id') and then enumerates exactly what is retrieved: prices, toll-free per-minute rates, number features, required documents, billing terms, and a purchase link. It also names the sibling search_areas as the source of the id, so an agent can place it in the workflow without opening the schema.

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 parenthetical '(from search_areas)' establishes the prerequisite step and implies the tool is used after a search to inspect a specific area. It does not state when NOT to use it or name alternative rate tools (get_calling_rate, get_forwarding_rate), so routing is implied rather than explicit.

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