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

No annotations are provided, so the description carries the full burden. It does add real behavioral context — currency defaults to GBP and the returned price excludes VAT — but omits other traits an agent would want: whether the lookup is authoritative/real-time, what happens on an invalid or non-registrable domain, rate limits, or auth requirements.

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 with zero waste, front-loaded with the core action and followed by the currency default and VAT caveat. Every sentence carries information.

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 2-parameter tool with no output schema and no annotations, the description covers the pricing semantics well but leaves gaps: the structure of the availability/price response, the unit of the price (per year vs one-time), and behavior on invalid input are all unaddressed.

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 0%, so the description must compensate. It does for currency (ISO format, defaults to GBP, superseding the schema's null default), but says nothing about the required domain parameter's accepted format (bare name vs FQDN vs URL). Partial compensation warrants a 3.

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 states a specific verb and resource: check domain availability plus registration price, scoped to UmbHost. This is clearly distinct from the sibling tools (list_plans, begin_checkout, quote, order_status) in substance, but the description never names or contrasts an alternative, so it lands at 4 rather than 5.

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?

There is no when-to-use guidance, no prerequisites, and no routing advice. A reader can infer it belongs before a registration flow, but nothing addresses the overlap with the sibling quote tool or when this should be preferred over a checkout flow.

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