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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so safety is covered. The description adds behavior the annotations do not: that the record is fetched live and that the response includes a policy interpretation plus a remediation suggestion — meaningful for a no-output-schema tool.

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, zero filler, and the selection trigger is front-loaded ahead of the return-value summary. Nothing here could be cut without losing information.

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 tool with rich annotations and no output schema, the description covers both when to call it and what comes back. The only real omission is how a missing or absent DMARC record is reported, which matters for a DNS-lookup tool whose negative results are common.

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?

There is a single required parameter with 100% schema description coverage including an example, so the schema does the work. The description adds no syntax, format, or edge-case guidance (e.g. subdomains, IDN, or whether a bare domain is required). 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?

The description pairs a specific resource (DMARC record) with what it returns: the live record, its policy, and a fix suggestion. That is enough to separate it from dkim_check and spf_check in principle, but it never names those siblings, so the differentiation is implicit rather than explicit.

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?

"Use this when the user asks about DMARC, spoofing protection, or what happens to emails that fail authentication" gives a clear trigger context, including the user-intent phrasings an agent will actually encounter. It stops short of exclusions or alternatives (e.g. route SPF questions to spf_check), so no score of 5.

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