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

With no annotations provided, the description carries the full burden. It discloses that RDAP is a third-party registry service, can be temporarily unavailable, and that a failure is upstream rather than caused by a bad query. This adds meaningful behavioral context beyond 'lookup' and indicates a read-only operation.

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 two sentences that front-load the result data, provide short use-case phrases, and include a caveat. Every clause earns its place with no wasted words.

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 single-parameter lookup tool with no output schema, the description is complete: it lists the returned data categories, gives usage scenarios, and explains failure behavior. One parameter makes complexity low, and the description covers all essential aspects.

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 input schema has 100% visibility: the domain parameter is described with a pattern, length constraints, and an example. The description doesn't add meaning beyond the schema, but it doesn't need to. Baseline 3 applies because schema does the work.

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 opens with a specific verb+resource: 'Fetch registration data for a domain via RDAP,' and enumerates concrete fields (registrar, dates, nameservers, EPP status codes). This clearly distinguishes the tool from siblings like dns_lookup or asn_lookup, which query different types of data.

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 provides explicit use cases: 'check domain age (a common trust signal), see when a domain expires, or find who it is registered through.' It does not name alternative tools or state when not to use it, but the context is clear enough given the sibling list.

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