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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, and openWorldHint=false, so safety is fully covered by structured data. The description adds nothing beyond that — no mention of aggregation behavior, time-range defaults, or whether results are grouped/sorted, which is what an agent would actually need here.

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?

It is short with zero redundancy, which is good, but it is a sentence fragment rather than a front-loaded, self-contained statement. Brevity here reflects under-specification rather than disciplined editing.

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 and a fragment description, an agent cannot know the response shape (per-ASN volume counts, ordering, aggregation window) or the effect of omitting the date range. For a reporting tool with a required domain ID, that is a meaningful gap.

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%, so the required domain 'id' and the optional ISO 8601 'from'/'to' dates are already documented. The description adds no syntax, default, or semantic nuance beyond the schema, 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?

The fragment 'DMARC message volume by sending network (ASN)' conveys the resource and the grouping dimension, so an agent can roughly tell it apart from list-dmarc-countries or list-dmarc-reporters. But there is no verb and no explicit statement of what is returned (counts? messages? per-ASN rows?), leaving the purpose only partially pinned down.

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 when-to-use guidance at all, and no routing to closely related siblings such as list-dmarc-sources, list-dmarc-countries, or get-dmarc-stats. The agent must infer the choice purely from the name.

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