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

Annotations already convey read-only, idempotent, open-world, and non-destructive behavior, and the description reinforces these with 'Read-only' and 'Cannot spend money.' The added behavioral detail about performing a live fetch of observable surface signals goes beyond the annotations and gives the agent useful safety and cost expectations.

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 compact and front-loaded: it opens with usage guidance, then lists the fetched fields, then states safety/cost constraints. Each sentence serves a purpose, though the two 'Use...' sentence stems could have been merged without loss of clarity.

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 one-parameter read-only tool with no output schema, the description is well-rounded: it covers input semantics, operation scope, the exact observable signals returned, and safety/spend constraints. Minor gaps like error handling for non-resolving domains and input normalization are acceptable given the simple, safe nature of the operation.

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 schema contains only a required 'domain' string with no descriptions, so the description must compensate. It adds meaningful semantic context by clarifying the domain is the user's existing/owned site, not a new candidate name. However, it does not specify the expected input format (e.g., bare domain vs protocol, trailing slash, punycode), leaving some ambiguity for invocation.

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/resource: 'Fetch a live domain's observable surface' and lists concrete outputs (HTTP status, redirect target, title, meta description, h1 headings, tech hints). It also distinguishes the domain from siblings by noting this is for names the user already holds, not for finding new ones.

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 explicitly tells the agent when to use the tool: when the user asks what is wrong with a site they own, wants an existing name assessed, wants to compare deployment against a spec, or wants to know if a domain serves anything. It signals when not to use it by saying 'rather than a new one found,' though it does not name specific sibling tools as alternatives.

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