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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds only that results are org-scoped custom domains; it says nothing about pagination, ordering, or whether unverified/pending domains are included, which is the kind of context that would earn a 4 or 5 here.

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 no filler. It is appropriately sized for a simple list tool, though its brevity comes partly from omitting useful detail rather than from tight editing of rich content.

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 one-parameter read tool with full annotation coverage this is close to sufficient, but there is no output schema and the description says nothing about the shape of the returned domain list or whether filtered/unverified entries appear. Minimal viable, with clear remaining 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?

Only one parameter exists and the schema documents it fully, including the provenance hint 'Organization ID from org_list.' The description adds nothing beyond what the schema already provides, so 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?

States a specific verb and resource ('Lists ... custom domains') scoped to an organization, which lets an agent distinguish it from domain_get, domain_attach, or domain_verify. It does not explicitly name a sibling alternative, so it stops short of a 5.

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 org-scoping ('an organization's') implies you call it with an org context rather than listing all domains, and the name makes the list-vs-get distinction evident. But there is no explicit when-to-use statement, no mention of alternatives such as domain_get for a single domain, and no prerequisites stated.

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