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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so safety is covered. The description adds useful context beyond that — result ordering, the four status values (pending, active, failed, removing), the failure-cause field, and the per-site domain quota — though it says nothing about permissions, prereqs, or pagination, and an output schema already carries the return shape.

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?

One front-loaded sentence covering resource, ordering, returned statuses, DNS records, and quota with no filler. Nothing could be removed without losing information.

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 single-parameter read-only list tool with full schema coverage and an output schema, the description is nearly complete: it explains ordering, status vocabulary, and the practical use of the DNS records. The only gap is the absent relationship to add_site_domain/verify_site_domain in the setup workflow.

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 coverage is 100% and the single siteId parameter is documented in the schema as coming from list_sites. The description adds no meaning beyond that; "of a hosted site" merely restates what siteId scopes. Baseline 3 applies when the schema does all the work.

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 and resource ("List the custom domains of a hosted site") and even states ordering ("oldest first"), so an agent immediately knows what comes back. It does not explicitly distinguish itself from siblings like add_site_domain, remove_site_domain, or verify_site_domain, but the "List" verb makes the read-only scope clear enough.

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?

Usage is only implied: an agent infers it should call this to inspect a site's domains and to retrieve the TXT/CNAME records needed for DNS setup. There is no explicit when-to-use, when-not, or routing to the obvious alternatives such as verify_site_domain once records are configured.

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