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

Annotations already declare readOnly/idempotent/closed-world, and the description adds genuinely new context: data comes from offline issuer files, no market call is made, and 13F figures reflect the latest reported quarter. It stops short of noting lag or coverage caveats (e.g. 13F reporting delay, ETFs outside the 54), which would push it to a 5.

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 answer, then the data provenance, then usage examples — a logical order with no filler. The parenthetical clauses are dense but each carries real information; the sentence is long enough that a skim may miss the 13F qualifier.

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 an output schema present and rich annotations, the description only needs to supply scope and provenance, and it does: 54-ETF universe, ISIN matching, latest-quarter 13F, offline/fast. Nothing required to call it correctly 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?

Schema coverage is 100%, so the baseline is 3; the description goes further by constraining the input to a US-listed stock and disclosing that matching happens on ISIN, which tells the caller that non-US listings or ambiguous tickers may not resolve. No format or edge-case guidance for tickers like 'BRK.B' beyond the schema examples.

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 question-answering resource: which of 54 tracked US ETFs hold a US-listed stock, plus which famous investors hold it per latest 13F. It names the data sources (issuer holdings files, ISIN match, 13F) and scopes the universe, so an agent can distinguish it from etf_holdings (forward lookup) and analyze_ticker 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?

Gives concrete trigger phrases ('which ETFs hold PLTR', 'does Buffett own Apple') that map cleanly onto the tool's purpose. It does not explicitly name a sibling to avoid (e.g. etf_holdings for the reverse direction), so the boundary is implied rather than stated.

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