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

With no annotations, the description carries the burden of behavioral disclosure. It does well by specifying that a nonexistent id or one from a different account is reported identically as 'not found', and it references the return fields as being the same as list_domains. It could have explicitly stated the operation is read-only, but 'look up' and the absence of side effects makes that reasonably clear.

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 with no filler. The first sentence states the purpose, the second explains the parameter prerequisite and return shape, and the third covers error behavior. Every sentence serves a distinct informational purpose and the most important information is front-loaded.

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-only lookup with an output schema, the description is nearly complete. It explains the parameter source, the return field equivalence, and the not-found edge case. The only minor gap is that it does not explicitly say 'this is a read-only operation' or cross-reference list_domains as the alternative for listing, but these are implied and the output schema covers return 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?

Schema coverage is 0%, so the description must compensate. It does so effectively by explaining that domain_id must be an id previously returned by list_domains, and it adds behavioral meaning by stating what happens for invalid or foreign ids. This goes beyond the raw schema type of 'integer' and gives the agent everything needed to provide a correct value.

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 ('Look up'), a specific resource ('one domain'), and a precise mechanism ('by its id'). It also names the sibling tool list_domains and clarifies that this is the singular counterpart, making the distinction 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?

It clearly states a prerequisite: the domain_id must come from a previous list_domains call. This implies the natural workflow of listing first, then fetching details, which gives clear context for when to use this tool versus list_domains. It does not explicitly say 'do not use list_domains for a single domain', but the instruction is effectively explicit enough.

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