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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuine value by disclosing the return shape { available, code, message } and the plan gating plus the create re-check note, which the annotations do not convey.

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 fragments, front-loaded with the core question and with zero filler. The 'Business plans:' opener is slightly clipped and could confuse, but nothing is wasted.

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 simple single-parameter availability check with no output schema, the description covers purpose, return shape, plan scoping, and the interaction with site creation. Remaining gaps (label format constraints, error semantics of 'code') are minor.

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% for the single required 'label' parameter, and the description only indirectly implies it is the address being checked. It does not state the accepted format or the 63-character limit, so it adds limited meaning beyond the schema's type/maxLength.

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 the check clearly enough via 'is this address free for a new site?' and names the resource (a site address/label). It is phrased as a question rather than a verb+resource statement, but an agent can tell this apart from sibling create/get/publish site tools.

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?

It signals when to call it (before creating a site, and only under business plans) and adds that 'the create call re-checks,' implying this is an optional pre-flight rather than a required step. No explicit alternative is named, but the context is clear.

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