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

Annotations already declare readOnlyHint=true, so safety is covered. The description adds real context beyond that: it discloses the data sources inspected (public DNS, SPF/DMARC, alignment) and that it performs 'live lookalike domain' checks, implying outbound lookups, plus it previews the return shape (A-F grade with findings).

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 tightly packed sentences: the grading action and evidence sources come first, the return value second. No filler, no repetition of the title.

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-only check with no output schema, the description supplies the missing return information (A-F grade plus findings) and the evidence sources. It omits only operational details such as lookup latency or rate limits, which is a minor gap.

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?

Only one parameter and schema description coverage is 100%, so the schema already documents 'domain' fully with an example. The description adds no format or syntax detail beyond what the schema provides, making the baseline 3 correct.

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 ('Grade') and a precise resource (a domain's exposure to email spoofing/BEC), and even names the evidence sources it draws on (SPF, DMARC policy strength, alignment, live lookalike domains). It is clearly distinct from analyze_eml or whois_lookup by its method, but it never explicitly contrasts itself with those siblings.

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 context of use is strongly implied by the purpose (assess a domain before trusting it, or audit your own), but there is no explicit when-to-use statement and no alternative tools named or excluded. Adequate but leaves routing to inference.

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