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

Annotations already declare readOnlyHint, destructiveHint=false, and openWorldHint=false, so the safety profile is covered. The description adds value beyond them by disclosing the required 'domains:read' permission, that it takes no input, and that an empty list is returned when the account has no domains.

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?

Three tight sentences: purpose and payload first, then constraints/permissions, then usage and scope exclusion. Every sentence earns its place 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?

With no output schema, the description still conveys what comes back (domains plus their DMARC reporting address) and the empty-list edge case, which is enough for a no-argument list tool. A little more on ordering or pagination would be needed for a 5.

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?

Zero parameters, so the baseline is 4; the schema is empty and there is nothing to misinterpret. The description's 'Takes no input' is consistent with the schema but adds no new semantic detail.

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 (List) and resource (domains) scoped to the signed-in user's MailVakt account, and specifies what is included (each domain's DMARC reporting address). The added clause 'does not enumerate domains belonging to other users' sharpens scope so the agent can separate it from sibling tools like add_domain or diagnose_domain.

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?

Explicitly states when to use it ('to find the account's available domains before requesting DMARC summaries'), which routes the agent toward get_dmarc_summary as the follow-up, and states the exclusion (does not enumerate other users' domains). Both the when and when-not are present.

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