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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds useful scope context (site-bound vs workspace-bound) and confirms the returned information (verification status), but does not go further into behavior like pagination or result shape. This is a solid but not exceptional addition beyond annotations.

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 sentence front-loads the action and then delivers the key conditional in a compact, readable way. There is no fluff or repetition; every clause earns its place.

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 the general return concept ('domains with their verification status') and covers the two invocation modes. It does not detail exact response fields or pagination, but for a straightforward read-only list tool the description is sufficiently complete for an agent 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 description coverage is 100%, so the baseline is 3. The description adds meaningful nuance beyond the schema by explaining the consequence of omitting site_id (return workspace-bound domains), which is not present in the site_id schema. This elevates it above baseline.

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?

The description uses a specific verb ('List') and resource ('custom domains'), and adds a clarifying qualifier ('with their verification status') that differentiates this read tool from siblings like add_custom_domain, verify_custom_domain, and remove_custom_domain. It also clearly identifies the two scopes (site-bound vs workspace-bound), leaving no ambiguity about what the tool does.

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?

The description gives clear context for choosing between the two invocation modes: pass site_id for site-bound domains, omit it for workspace-bound aliases. It does not explicitly name alternatives or state when-not-to-use, but the parameter-level guidance is actionable and unambiguous for the main usage scenarios.

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