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

Annotations already carry readOnlyHint, openWorldHint, idempotentHint and destructiveHint=false, so the description adds value by naming the RDAP source and expected fields. It does not discuss potential rate limits, failures, or formatting nuances, but with rich annotations the burden is lower.

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 short sentences: the first front-loads the purpose and output fields, the second provides a clear sibling alternative. 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 one-parameter read-only tool with no output schema, the description gives enough field-level expectations for an agent to interpret the result and names the correct sibling. It stops short of describing edge cases like missing domains or RDAP availability, but those are minor given the annotations.

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 already fully documents the single domain parameter (100% coverage). The description reinforces that it is a domain for registration details and gives an example, but adds no new syntax or format semantics beyond the schema.

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?

States a specific action (look up) and resource (domain registration data via RDAP), and enumerates concrete data points (registrar, dates, age, nameservers). It also distinguishes itself from the sibling dns_lookup by clarifying it covers registration data rather than DNS records.

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?

Explicitly routes agents to dns_lookup when DNS records are needed, and clearly implies this tool is for registration details. This is an explicit alternative with a condition, leaving no ambiguity about when to choose it over the closest sibling.

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