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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, covering the safety profile. The description adds context about what a custom domain is and the status filter, but does not disclose additional behaviors such as pagination or response format. Since the schema includes page_size and page_token, pagination is implied but not explicitly mentioned. Given annotations, the description contributes limited additional behavioral transparency.

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?

The description is two sentences, with the first sentence stating the action and scope clearly. The second adds a helpful explanation of custom domains and the optional filter. It is front-loaded, concise, and contains no unnecessary words.

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?

The tool is simple with no required parameters, read-only, and idempotent. The description covers the purpose, resource definition, and filter. The schema and output schema provide pagination and response details. Nothing essential for an agent to call this tool 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 descriptions cover all three parameters fully: status enumerates values and 'omit for all', page_size and page_token are clearly explained. The description adds only a brief mention of the status filter, which is redundant with the schema. With 100% schema coverage, the baseline of 3 is appropriate; the description does not add new semantic meaning beyond the schema.

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 clearly states the action (List), resource (custom domains), and scope (authenticated tenant). It also explains what a custom domain is, which distinguishes it from other domain-related tools like get_custom_domain (singular) and create/update/delete. The purpose is unambiguous.

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 does not explicitly mention alternatives or when not to use this tool. The naming and purpose imply it is for listing, and the presence of get_custom_domain suggests using that for a single domain, but this is not stated. The optional status filter provides some usage context, but there is no explicit routing to alternatives.

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