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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the safety profile is covered. The description earns credit beyond that by scoping results to the authenticated tenant and explaining what a custom domain actually represents (serving dynamic endpoints on the customer's hostname instead of the default URL). It does not mention pagination behavior, but that is documented in the schema.

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 sentences, front-loaded with the action and scope; the filtering hint lands last where an agent looks for it. The middle sentence on domain semantics is slightly expansive but still earns its place by clarifying what the listed entities are.

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?

An output schema exists so return shape needn't be described, pagination params are covered by the schema, and annotations carry the safety profile. What remains is the tenant scoping and domain semantics, which the description supplies. Nothing an agent needs in order 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?

Schema description coverage is 100%, so all three parameters are already documented, including the exact status enum values. The description's 'Optionally filter by lifecycle status (PENDING, VERIFIED, CERT_PENDING, ACTIVE)' restates what the schema already says without adding format or edge-case detail. 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?

Opens with a specific verb+resource and a clear scope: 'List the custom domains claimed by the authenticated tenant.' This separates it from get_custom_domain, create_custom_domain and update_custom_domain by naming the tenant-wide collection, though it never explicitly names those siblings.

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?

It says the status filter is optional and enumerates the values, which is mild usage guidance for the parameter. But there is no explicit statement of when to reach for this versus get_custom_domain for a single domain, and no exclusions or prerequisites — usage is implied rather than directed.

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