purchase_email

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

No annotations are provided, so the description carries the full burden of behavioral disclosure. While 'purchase' implies a paid action, it does not explain prerequisites, reversibility, cost implications, or what happens after the activation is purchased.

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 description is very brief and front-loaded, consisting of a single sentence. It is not verbose, but it lacks sufficient content to be fully informative. Still, it earns a moderate score for being appropriately sized.

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?

The tool is simple with two parameters and no output schema, but the description does not clarify the expected result or side effects of the purchase. For a mutation tool, this is a significant gap; the agent is left guessing what the response contains or what state changes occur.

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?

The input schema already provides descriptions for both parameters (site and mailDomain), giving 100% schema coverage. The description adds no extra meaning about the parameters, so the baseline score of 3 is appropriate.

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?

The description uses a specific verb ('purchase') and identifies the resource ('email activation'). It is clear enough to differentiate from read tools like get_email_status, but does not explicitly distinguish from related email tools like reorder_email or cancel_email.

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 description provides no guidance on when to use this tool versus alternatives. It does not mention relationships to sibling tools such as get_email_domains or request_number, leaving the agent without context for selection.

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