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

Annotations already provide the safety profile (readOnlyHint=true, idempotentHint=true, destructiveHint=false). The description adds meaningful behavioral context by specifying the DNS record types queried, which is not covered by annotations. It does not describe return format, but the output schema handles that, making this a solid addition beyond the structured metadata.

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 a single, information-dense sentence that front-loads the main action and follows with a list of DNS evidence types. While the acronym list makes it slightly dense, every word serves a purpose and there is no redundant verbiage. It is concise enough for a technical tool.

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?

With an output schema present and clear annotations, the description sufficiently covers the tool's function and scope. It mentions the key input (domain) and implicitly covers the optional DKIM selectors. It does not discuss limitations or specific use-case boundaries, but for a read-only diagnostic tool with two parameters, this is adequate.

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 both parameters (domain, dkim_selectors) have thorough descriptions. The description's phrase 'caller-selected DKIM' reinforces the dkim_selectors parameter but adds no new semantics. The schema already does the heavy lifting, so a baseline score of 3 is appropriate.

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 clearly states a specific verb ('Check') and a well-defined resource ('public domain's email authentication and anti-spoofing posture'). It enumerates the exact DNS evidence types (MX, SPF, DMARC, DKIM, MTA-STS, TLS-RPT, BIMI), which makes its purpose distinct from sibling tools like web.domain-intelligence or web.security-audit.

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 implies the tool's use case (checking email authentication for a public domain) but does not explicitly state when to use it over alternatives. No exclusions or alternative tool names are mentioned. The context is clear, but the description lacks explicit guidance on decision-making between this and related web security tools.

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