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

Annotations already declare readOnlyHint=false, destructiveHint=false, and openWorldHint=false, so the safety profile is known. The description usefully narrows the mutation scope to primary status and role, but omits meaningful side effects an agent would want to know, such as whether setting a new primary demotes the existing one or what role changes imply for live traffic. Given annotation coverage, a 3 is appropriate.

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?

A single front-loaded sentence with the verb and the two supported actions; there is no filler or redundancy.

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?

For a mutation tool with no output schema and only 33% parameter coverage, the description is serviceable but thin: it never says what happens to the previously primary domain, whether authorization is required, or what the call returns. It is adequate to call the tool but leaves real gaps.

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 only 33%: role carries a rich enum description in the schema while id and isPrimary are undocumented. The description partially compensates by mapping its two stated operations onto isPrimary ('make primary') and role ('change its role'), but adds no format or constraint detail for id or isPrimary.

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 (update) and resource (domain) and names the two operations the tool supports: promoting a domain to primary and changing its role. This is distinguishable from the sibling domains_create/delete/list/verify, which do different things. It falls short of a 5 only because it does not explicitly contrast itself with domains_verify, which also touches an existing 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?

There is no guidance on when to use this tool versus the alternatives (domains_verify for verification, domains_create for adding a domain, domains_list for reading). The two supported operations are implied by the sentence but no preconditions or context for choosing this tool are given.

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