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

With readOnlyHint=true already covering the safety profile, the description adds genuinely useful behavior: required scopes (domains:read, reports:read), the zero-totals outcome when no reports exist, and an error when the domain is not in the account. It stops short of disclosing pagination or any rate/volume limits.

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?

Front-loads the action and scope, then the parameters, then returned data, then permissions and edge cases, in one tight block. Every sentence carries distinct information with no filler.

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?

There is no output schema, so the description correctly summarizes the return payload (report and message totals, pass/fail counts, per-source alignment and receiver actions). Error and empty-result cases are also covered, leaving nothing an agent needs to call it correctly.

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 coverage is 100%, and the description largely restates what the schema already provides (1-to-90-day window, default 7, domain belonging to the user). It adds no syntax, format, or edge-case detail beyond the structured fields, 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 (summarize) and resource (received DMARC aggregate reports) scoped to a domain in the signed-in user's account. It is clearly distinguishable from siblings like add_domain, list_domains, and diagnose_domain because it explicitly reads existing reports rather than creating domains or diagnosing.

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?

Gives a clear precondition (domain must already be in the user's MailVakt account) and a negative boundary ('Does not add domains or generate report traffic'), which implicitly steers the agent away from add_domain. It does not, however, name a specific alternative tool for the domain-not-found or domain-addition cases.

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