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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and a closed world, so the safety profile is fully covered without the description. The description adds that the result is a TXT record intended for publication at a specific DNS location, which is useful output context, but says nothing about validation behavior, errors on invalid input, or whether the record is deterministic for the same inputs.

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?

A single front-loaded sentence with no filler; the verb and produced artifact come first and the qualifier about where to publish follows. Nothing here is wasted or redundant.

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 no output schema, the description must carry the return-value burden; it does state at a high level that the output is a DMARC TXT record for _dmarc.yourdomain. However, it leaves out how optional inputs shape the record (sp tag, rua tag) and gives no sense of the actual returned string or structure, which is a meaningful gap for a generator tool.

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 only 50% ('domain' and 'subdomainPolicy' carry no description), so the description is expected to compensate. Instead it only echoes the two already-documented inputs ('policy and report addresses') and says nothing about the required domain field or how subdomainPolicy maps to the DMARC sp tag.

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 gives a specific verb ('Build') and resource ('a valid DMARC TXT record') plus the intended publication location (_dmarc.yourdomain), so the agent knows exactly what artifact this produces. It does not explicitly contrast itself with the sibling check_dmarc or generate_spf_record/generate_dkim_record, but the resource specificity makes the distinction clear.

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?

There is no statement of when to use this tool versus the check_* or other generate_* siblings, and no prerequisites (e.g. that a domain must exist or that this is a generation step in an email-setup workflow). The phrase 'from a policy and report addresses' only restates the inputs, not usage context.

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