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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=true, so the safety profile and the external-network nature of the call are covered without description help. The description adds genuinely useful context the annotations do not: the 10-credit cost. It does not say what happens for domains with no DMARC record or what an invalid-config result looks like.

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 a single sentence, which is appropriately short, but the name and title are redundantly restated ('DMARC Validator: DMARC Validator is a DMARC record validator API'), burning roughly a third of the text on repetition. The credit cost is appended in parentheses rather than woven into the flow.

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?

The tool is simple (one required parameter, annotations present, output schema available), so the description does not need to explain return values. What is missing is selection context against the closely related SPF/DKIM/BIMI/DANE validators and any note on behavior for domains lacking a record — the two things an agent most needs before calling.

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 parameter with 100% schema description coverage, so the schema already explains that 'domain' is the domain whose DMARC record is validated. The description adds no format hints (e.g., bare domain vs. subdomain, no scheme) beyond the schema's example. Baseline 3 applies when the schema does the heavy lifting.

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 names a specific verb and resource: it 'checks the DMARC record for a domain' to verify correct configuration. That is clearly distinguishable from a generic DNS lookup. However, it never distinguishes itself from the family of sibling validators (SPFValidator, DKIMValidator, BIMIRecordValidator, DANERecordValidator), which an agent must pick between.

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 explicit when-to-use or when-not-to-use guidance. The phrase 'ensure it is correctly configured' implies a validation scenario, but nothing tells the agent to prefer SPFValidator or DKIMValidator for the other email-authentication records, nor what to do if the domain has no DMARC record at all.

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