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

With no annotations supplied, the description carries the transparency burden and does a good job: it explicitly declares the return scope and states an unusual negative guarantee ('Never a key hash, billing field, or call log'). It does not spell out idempotence or auth/rate-limit behavior, though 'Return' and the whoami semantics imply a safe read.

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 packed sentences: the first leads with the verb, resource, and full field list; the second adds a valuable negative guarantee without restating any schema information. No wasted 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?

With no output schema, the description compensates by naming the exact return fields and the optionality of the handle. It omits explicit error cases or detailed types for contact_policy/plan, but for a zero-required-param self-identity tool the provided context is nearly sufficient.

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 description coverage is 100% for the single optional tenant_key parameter, which already documents the Bearer-header precedence. The description adds no parameter semantics, but none are needed; the baseline of 3 applies because the schema handles the parameter documentation.

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 ('Return') and identifies a distinct resource ('this tenant's own agent-directory address'), then enumerates the exact fields returned: namespace, handle, display name, contact_policy, plan. It does not explicitly contrast with the sibling host.whoami, but the 'agent-directory' qualifier and field list make the tool's purpose clear.

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 phrase 'this tenant's own' implies when to use it as a self-identity lookup, and 'Never a key hash, billing field, or call log' provides a boundary. However, there is no explicit guidance about when to prefer it over sibling tools like host.whoami or host.agent.lookup/search, so routing between alternatives is left to inference.

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