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

Annotations already declare readOnlyHint=true, idempotentHint=true, openWorldHint=false, and destructiveHint=false, so the safety profile is covered. The description adds meaningful behavioral context by specifying what information is returned, including lifecycle status, DNS records, routing details, and human-facing check/certificate messages.

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?

Two tightly written sentences, front-loaded with the operation and followed by concrete use cases. Every sentence earns its place and there is no redundant or vague text.

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 read-only single-resource lookup with one fully documented parameter, rich annotations, and an output schema, the description is complete. It explains the returned information and practical usage without needing to duplicate schema details.

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?

The single hostname parameter is fully documented in the schema with an example ('shop.customer.com'), and schema description coverage is 100%. The description reinforces that lookup is by hostname but does not add syntax or formatting details beyond what the schema already provides, so the baseline of 3 is appropriate.

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 states a specific verb and resource ('Get a single custom domain by hostname') and scopes it to a single lookup rather than a list. It also enumerates the returned facets (lifecycle status, DNS records, routing, messages), making it clearly distinct from sibling tools like list_custom_domains, create_custom_domain, and verify_custom_domain.

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 gives clear usage context: answer 'is my domain live yet?' and re-display DNS records for a pending domain. However, it does not explicitly name alternatives or exclusions, such as when to use list_custom_domains or verify_custom_domain instead.

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