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

Annotations already declare read-only/idempotent, but the description adds meaningful behavioral detail: queries are made live against Cloudflare, Google, and Quad9, and the email grading logic is specified precisely. This goes well beyond what annotations provide.

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 sentences, each earning its place: what is returned, how it is queried, and the grading criteria. The most important information is front-loaded, and there is no redundancy with the schema or annotations.

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 rich annotations and no output schema, the description fully covers input, record types returned, grading behavior, live resolution sources, and pricing. Nothing an agent needs to call it correctly 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?

The schema only says 'domain' is a required string with no description, so the description must compensate. It does by clarifying that the input is a domain whose DNS records are fetched. While it doesn't specify formatting examples, the single parameter is unambiguous enough for correct invocation.

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 names the exact resource (all DNS record types plus SPF/DMARC) and the outcome the agent can expect: knowing where a domain points and whether email can be spoofed. This clearly distinguishes it from siblings like domain_whois or tls_check by scope and output.

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 gives clear context for when to call it: whenever domain infrastructure or email spoofability is in question. It does not explicitly name alternatives or state when not to use it, but the use cases are concrete enough for an agent to route correctly.

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