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

Despite annotations already covering the safety profile, the description adds substantial behavioral context: idempotent semantics for repeated calls, the domains:write permission requirement, and an explicit list of things it does NOT do (no ownership verification, no DNS modification, no reports until DNS is published). This is exactly the kind of extra disclosure annotations cannot carry.

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?

Four compact sentences, each carrying distinct information (purpose, return value, idempotency, permission, non-behaviors), with the primary purpose front-loaded in the first clause.

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?

No output schema exists, yet the description summarizes the return value (the DMARC rua address and account entry), states idempotency, the permission needed, and the boundary conditions. An agent has everything needed to call it correctly and interpret the result.

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% with a single required domain parameter whose format and example are already documented in the schema. The description's 'Takes a domain' restates the schema without adding syntax, normalization, or validation detail, 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 and resource ('Add a domain to the signed-in user's MailVakt account') and narrows the scope to 'DMARC report collection', which cleanly separates it from read-oriented siblings like list_domains and configure-oriented ones like generate_dns_records.

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 clear context for when to reach for it (adding a domain for DMARC report collection) and spells out the resulting precondition (the reporting address must be published in DNS before reports flow), plus the domains:write prerequisite. It does not name an alternative tool to use instead in any scenario, so it falls short of a full when/when-not/alternatives statement.

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