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

Annotations already declare readOnlyHint=true and destructiveHint=false, and the description adds meaningful behavioral context beyond that: the verdict scale, 0-100 risk range, the exact data sources fused, the one-call bundling behavior, and the per-call price. No contradiction with the annotations.

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?

Three dense, purposeful sentences deliver verdict/risk, data sources, use case, and price without filler. The most decision-relevant information is front-loaded.

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?

There is no output schema, so the description correctly covers the return values (verdict + risk) and enough behavioral context to choose the tool. However, it does not resolve how to provide email vs domain when both are listed as required, which is important for actually calling it successfully.

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 coverage is 100%, so the baseline of 3 applies. The description only echoes the 'email or domain' idea and does not clarify the tension between the required[] listing both fields and the 'or use domain' phrasing, leaving an invocation ambiguity.

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 states a precise output (TRUST/REVIEW/REJECT verdict plus 0-100 risk) for an email address or sending domain, and names the fused data sources (SPF/DMARC, RDAP, hosting-IP threat reputation). This clearly distinguishes it from narrower sibling tools like dns_lookup or email_domain_check.

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?

It explicitly scopes the tool to 'agents filtering inbound mail, leads and senders before acting,' which provides strong context for when to use it. It does not name sibling alternatives or state when not to use them, so it stops short of full routing guidance.

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