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

Annotations already cover safety (readOnlyHint=true, destructiveHint=false) and open-world access, so the bar is lower. The description still adds real behavioral context: the data is normalized RDAP and resolution is restricted to five specific RIR registries, which is a scoping constraint not present in the structured fields. It does not say what happens when a handle falls outside those registries.

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 with no filler. The core capability and examples come first, and the RIR limitation plus the domain-lookup redirect are packed into the second sentence.

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 read lookup with full annotation coverage and no output schema, the description is nearly sufficient. The only gap is that it never characterizes the returned RDAP entity payload, so an agent knows what it retrieves but not what shape to expect.

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 100% and the single handle parameter is already documented with the same examples in the schema. The description repeats rather than extends that meaning, so the baseline of 3 applies.

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 verb (look up) and resource (normalized RDAP data for an RIR entity handle), and immediately grounds it with concrete handle examples like "GOGL" and "ORG-RIEN1-RIPE". It also isolates itself from the closest sibling by naming domain-lookup as the tool for registrar/registrant 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?

Gives a clear when-not condition (only ARIN, RIPE, APNIC, LACNIC and AFRINIC handles resolve) and routes one adjacent case to domain-lookup. It does not address the other siblings (asn-lookup, ip-lookup, nameserver-lookup), so the alternative coverage is partial rather than exhaustive.

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