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

Annotations already declare readOnly, idempotent, non-destructive, closed-world. The description adds genuine behavioral context beyond that: results are UIDs newest-first, the subject is excluded from its own results, and an empty 'basis' means no address or provider rather than isolation. That last clarification prevents a real misinterpretation.

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?

Front-loaded with the core action and scope before the edge-case caveats. Dense and slightly clause-heavy in the middle ('the fiduciary it is domiciled at, matched as mailbox detection counts mass domiciliation'), but every sentence carries information an agent would otherwise guess wrong.

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?

An output schema exists so return shape need not be explained, yet the description still usefully previews the return (UIDs, newest first, basis semantics) and the input constraint on uid. Complete for a read-only pivot tool; only the absence of sibling routing keeps it below a 5.

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%, so the baseline is 3, but the description adds meaning the schema does not: the uid must be a company UID and a c/o string is never accepted as a pivot. It says nothing extra about size or cursor, which the schema already documents adequately.

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 — companies sharing one company's address, pivoted by UID — and explicitly carves out what it is not ('a c/o string is never accepted', 'the subject is left out'). An agent can distinguish it from siblings like list_company_uids_at_address and search_companies without opening a schema.

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 invocation context: pivot from a UID, and it will not accept a c/o string as input. It does not name an alternative sibling or state when-not to use this versus list_company_uids_at_address, so it falls short of fully explicit routing.

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