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

Annotations already cover the safety profile (readOnlyHint=true, destructiveHint=false, openWorldHint=false). The description adds context the annotations cannot carry: the required domains:read permission and the empty-list return when the account has no domains. It stops short of describing result ordering or pagination.

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: what it returns, what it requires, and when to use it. The most decision-relevant facts (scope, permission, empty-list behavior) are front-loaded and nothing is padding.

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 carries the return-value burden and does so: it names the domain list and the DMARC reporting address field, plus the empty-list edge case, and identifies the permission needed. Nothing an agent needs to call it correctly is missing.

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?

The tool takes zero parameters, so there is no argument semantics to explain; the description correctly states 'Takes no input.' Baseline for zero-param tools 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 (List) and resource (domains) scoped to the signed-in user's MailVakt account, and names the field of interest (DMARC reporting address). It also explicitly declares the boundary 'does not enumerate domains belonging to other users,' which separates it from any account-wide or sibling lookup.

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 workflow guidance ('Use to find the account's available domains before requesting DMARC summaries') and one exclusion (other users' domains). It does not, however, name which sibling to call for a filtered or per-domain view, so the routing is implied rather than exhaustive.

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