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

Annotations already declare readOnly=true, idempotent=true, openWorld=true, destructive=false, so the safety profile is settled. The description adds genuinely non-structured context: the pricing model ($0.0018 per ownership-row), the fact that each returned row is a charged event, and that 13F results include changes vs the previous quarter. It does not disclose pagination behavior, whether all parameters are optional and which defaults apply, or any rate/row-cap implications beyond the per-row cost.

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?

The structure is front-loaded: the core question, then a compact enumeration of the four data sources, then the price. There is minor filler ("For investors, analysts and AI agents"). The long single sentence is dense but each clause maps to a distinct mode, so little is wasted.

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?

For a 13-parameter, four-mode tool with no required parameters and no output schema, the description covers what data comes back conceptually but not what a returned ownership row looks like or how to page beyond maxResults. It also leaves mode-selection and the insider-sale overlap with sec_insider_trades for the agent to infer. Adequate to get a call made, but not complete for a tool of this complexity.

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?

With schema description coverage at 100%, the schema already documents every one of the 13 parameters including per-mode applicability. The description only reinforces the mode semantics ("13F, with changes vs the previous quarter", "who filed a 5%+ stake") and names example fund/ETF tickers. It adds no syntax or format detail beyond what the schema supplies, so baseline 3 is appropriate.

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 gives a concrete framing ("Who owns a stock and who is about to sell it, from official SEC filings") and then enumerates exactly what each form type yields (13F holdings with quarter-over-quarter changes, N-PORT fund/ETF holdings, 13D/13G stakes, Form 144 planned sales). It is far more specific than the title alone. It stops short of naming how it differs from the sibling sec_insider_trades, which overlaps with the Form 144 / insider-selling territory.

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?

Usage is conveyed by example domain (a fund like Berkshire, an ETF like VOO/ARKK, a 5%+ stake filer, an insider filing to sell), which implies when to pick this tool. However, there is no explicit when-not guidance, no mention of the alternative sibling tools, and no statement of how to choose between the four modes at the description level — that choice is left entirely to the schema's mode enum.

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