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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so the safety profile is covered by structured data. The description adds genuinely new operational context by disclosing the 1-credit cost and the fact that results come from external live lookups; it does not contradict the annotations.

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?

Two sentences, zero filler: the first front-loads exactly what data the agent gets, the second front-loads the cost. Every clause carries information an agent needs for selection.

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?

With no output schema, the description usefully substitutes by enumerating return categories. However, it omits the api_key authentication path and gives no failure behavior (e.g., nonexistent domain, lookup timeout), which matters for an openWorld read against external registries.

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 for both parameters and does not. The domain parameter is only inferable from context, and the api_key parameter (a default-empty auth credential) is never mentioned anywhere, leaving the authentication requirement undocumented.

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 names the exact resource (a domain) and enumerates the precise data classes returned: DNS record types (A/AAAA/MX/NS/TXT), RDAP registration fields (registrar, created/expiry dates, status), and SSL certificate days remaining. No sibling tool (credit, key, or email verification) overlaps with this scope, so an agent can select it unambiguously.

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?

Usage is implied by the enumerated outputs – call it when you need DNS/RDAP/SSL data for a domain – but there is no explicit when-to-use statement, no prerequisites, and no named alternative. The 'Costs 1 credit' line hints at a budget consideration but doesn't guide tool selection.

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