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

The description discloses a critical behavioral detail beyond annotations: if ssn_last4 is present, the request fails with INVALID_ARGUMENT and writes nothing. It explains the rationale (digits are only recorded by SetOwnerTaxIdentifier after full identifier storage), giving the agent a clear understanding of side effects and failure modes.

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 dense sentences with no filler. The core purpose is stated first, followed immediately by the critical constraint. Perfect front-loading and zero waste.

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?

Given the presence of an output schema, the description need not detail return values. It covers the primary operation (upsert) and the one critical edge case (ssn_last4 refusal). For a single-purpose banking tool, nothing essential is missing.

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 description adds crucial meaning for the ssn_last4 parameter, stating it must not be used here and why. This is the most constrained field and the description compensates for the 50% schema coverage by highlighting the key semantic. Other parameters are left to schema descriptions, which is acceptable given their straightforward nature.

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 clear verb (Upsert) and resource (beneficial owner), and distinguishes itself from sibling tools like banking_set_owner_tax_identifier by explicitly declaring that ssn_last4 is refused. It makes the tool's scope and boundary 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?

The description gives a specific when-not scenario: do not pass ssn_last4; use SetOwnerTaxIdentifier instead. This routes the agent to the correct alternative for that data. It does not cover other hypothetical alternatives, but for a narrow upsert tool this is sufficient guidance.

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