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

Annotations already declare readOnly/idempotent/non-destructive, so safety is covered. The description adds real context beyond that: each service is returned once per call in a single language, results bundle service plus its plan options, and it flags that the paid-order and checkout paths are only listed while those channels are enabled.

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?

The routing information is front-loaded and every sentence carries signal. The final sentence is a run-on with nested parentheticals and a duplicated 'instead' ('...or create_checkout when a person will pay... instead of defaulting to the cheapest'), which costs some readability.

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, the description compensates by enumerating the return shape (service id, name, platform, starting price per 1000, plus plan options with id, name, price per 1000, min/max quantity) and by pointing to the pagination fields. Nothing an agent needs to call and chain this tool 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 the baseline is 3 and the schema already documents each filter. The description still adds value by telling the agent to pass concrete keywords to query and to map natural-language intent (budget, country, speed) onto the structured filters, which is usage semantics the schema does not state.

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 ('Searches the sellable social growth service catalog') and explicitly frames itself as the entry point. It names siblings get_service and recommend_service and the condition under which each is preferred, so an agent can differentiate without opening any 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?

Gives explicit when-to-use ('START HERE when you do not yet know which service to buy'), two when-not-to-use branches with named alternatives, and the downstream routing (pass service_option_id to get_quote/create_paid_order or create_checkout). Nothing is left to inference.

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