Generate a free subdomain

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

The annotations already mark this as a mutating action (readOnlyHint=false) with no destructive behavior. The description adds useful context that the subdomain is free and unique, and that a custom domain can be connected later, but it doesn't disclose what is returned or any limits/side effects beyond that.

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 short and front-loaded with the core action. The second and third sentences add useful context about immediacy and future custom-domain use, though they are slightly redundant with the first sentence's 'without purchasing custom domains' clause.

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 zero-parameter generation action, the description is sufficient: it explains what is generated, why it is useful, and how it fits into the broader hosting workflow. The lack of an output schema is acceptable because the purpose is simple and the generated subdomain is the clear output.

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 tool has zero parameters, and the schema description coverage is 100%. There is no parameter semantics burden for the description to carry, so a baseline of 4 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 ('Generate') and resource ('a unique free subdomain'), making the tool's purpose immediately obvious. It clearly distinguishes itself from custom-domain purchase flows and website subdomain tools by emphasizing that no purchase is needed.

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 implies when to use the tool: when you want to start hosting immediately without purchasing a custom domain. However, it does not explicitly name alternatives or say when not to use it, leaving sibling differentiation to inference.

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