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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint, and non-destructive behavior, lowering the bar. The description still adds useful domain context by enumerating the exact checks performed (_dmarc existence, policy, reporting, outdated tags) and the practical meaning of the result (impersonation exposure).

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 sentences, front-loaded with what is inspected and closed with the interpretation, with no redundant or filler content.

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?

No output schema exists, so the description must convey returns; it does so by listing the record attributes examined and the impersonation verdict. Minor gaps remain around the no-record case and the precise response shape, but it is adequate for a single-domain read-only lookup.

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 that a URL or email address is accepted. The description adds no syntax or format detail beyond that, so the baseline 3 applies.

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 (Check) and resource (domain's DMARC record) and enumerates what it inspects: existence at _dmarc, policy values, report collection, outdated tags, and impersonation risk. It is unambiguous, but it never differentiates itself from siblings like check_spf, check_dkim, or check_domain_email_setup, which likely overlap.

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 closing sentence ('Tells you whether the domain can be impersonated by email') implies a usage context for email-security assessment, but there is no explicit when-to-use, when-not-to-use, or pointer to the sibling tools that cover the rest of an email-auth audit. Usage must be inferred.

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