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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, openWorld), yet the description adds real behavioral context beyond them: the response discloses a name_match grade (exact/starts_with/contains) plus other candidates, and a substring match is never silently presented as the fund. It also discloses coverage asymmetries between N-CEN Part F and the UIT section.

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?

Long but information-dense and front-loaded, with the key differentiator (explicit ETF flag absent from N-PORT) leading. Every sentence carries a distinct fact, though the density and parentheticals make it heavier than strictly necessary.

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?

No output schema exists, and the description compensates by describing return content (fields, match-grade disclosure, candidate list) and coverage gaps (no expense ratio/NAV/adviser for UIT ETFs). For a one-parameter lookup this is complete.

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?

Only one parameter and schema description coverage is 100%, so the schema already carries the semantics; baseline is 3. The description reinforces behavior by supplying concrete name examples ('Vanguard Total Stock Market Index Fund', 'SPDR S&P 500 ETF Trust'), but adds no syntax or format detail the schema lacks.

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?

States a specific verb+resource (fund/ETF profile from SEC Form N-CEN) and enumerates the exact fields returned (ETF/index/MM status, AUM, expense ratio, advisory fee, NAV, adviser). It also names the sibling it is not (nport_fund_portfolio) and carves out the UIT-ETF variant, so it is distinguishable without opening any 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?

Explicit when-to-use ('is this fund an ETF', 'expense ratio', 'who manages this fund', 'AUM') and when-not ('Does NOT cover inception date ... or portfolio holdings (use nport_fund_portfolio for that)'). The alternative tool and the condition that selects it are stated outright.

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