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

Annotations already declare readOnlyHint=true and destructiveHint=false; the description reinforces this with 'Nothing is bought' and adds genuinely new behavioral context: the Pro account requirement and the required hand-off to request_business_number. It does not discuss result volume or pagination, but an output schema exists so return shape is covered elsewhere.

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 search scope, then the no-purchase constraint, then the alternative and prerequisite. No filler and nothing repeated.

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-optional-parameter read-only search with full schema coverage, annotations, and an output schema, the description covers everything an agent needs: scope, cost, prerequisite, and the exact next call. Nothing relevant 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 coverage is 100% and the single parameter already carries its own pattern and example ('like 2024 (up to 10)'). The description's '`contains` matches digits' restates the schema rather than adding new semantics, so the baseline 3 applies.

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 and resource with qualifying scope: 'Search US toll-free numbers that can text and are free to buy.' An agent immediately knows what comes back. It does not explicitly distinguish itself from the sibling list_numbers (presumably owned numbers), which is the only gap.

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?

Explicitly says this is a lookup, not a purchase ('Nothing is bought'), names the follow-up tool to invoke (request_business_number), and states the required user-facing action (give the user the link). It also declares the prerequisite (Pro account), so the agent knows when the call will fail.

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