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

Annotations already declare readOnlyHint=true and destructiveHint=false, so no contradiction exists. The description adds valuable behavior beyond that: it explains the three possible comparison outcomes (match, appears only in verbatim quote, or differs with the register's value) and promises to return the source page and quote for traceability. This gives the agent a realistic expectation of the tool's semantics.

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, front-loaded with the user's implicit question, and every clause earns its place. It explains the tool's purpose, input semantics, output categories, and traceability without repetition or filler.

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 read-only verification tool with a high-coverage input schema and an output schema, the description fully covers what an agent needs: what the tool does, what it checks against, what outcomes it reports, and what supporting evidence it returns. No critical behavioral or prerequisite information is missing.

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%, so the schema fully documents claimed_value, iana_id, and field. The description reinforces that the claim should be taken literally and that omitting field means all fields are checked, but it adds little beyond what the schema already provides. A baseline 3 is appropriate because the description is not needed to compensate for gaps.

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 the pointed question 'Is this right?' and states a specific verb and resource: 'Check a claim about a registrar ... against the register.' It enumerates example claims (accreditation status, name, enforcement date) and clearly distinguishes itself from a data-fetch or listing tool by emphasizing verification over retrieval. This gives an agent an unambiguous understanding of the tool's unique role.

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 clearly conveys when to use the tool: whenever a claimed registrar fact needs to be checked 'instead of trusting it.' It does not explicitly name sibling alternatives such as get_registrar or resolve_registrar, nor does it state when not to use it, so it stops short of a full 5.

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