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

Annotations already cover the read-only safety profile, yet the description layers on genuinely non-obvious behavior: boards count only filers present in both quarters, Δ Value includes price movement on held shares and can be zero, and the tool refuses comparisons crossing the corpus boundary. These are substantive caveats an agent could not infer from the schema.

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 purpose, then the bucket semantics and caveats. Dense but almost every clause carries actionable information; the Δ Value/Δ Shares distinction is the one slightly verbose stretch, but it is useful.

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 no output schema, the description still conveys what is returned (leaderboards of ranked stocks with count-based or value-based ordering) and the corpus-boundary constraint on the report quarter. For a single required enum-style parameter plus two optional ones, nothing an agent needs 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 already 100%, but the description adds real meaning beyond it: each bucket's ranking criterion (Δ shares sign and Δ value ordering, or count of initiating/exiting filers) is spelled out. It clarifies selection logic the enum-style schema line does not.

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 precise verb+resource ('get the market-wide 13F leaderboards for a given quarter') and enumerates the exact four views it can produce. The 'market-wide ... across all 13F filers vs the prior quarter' scope cleanly distinguishes it from institution-scoped siblings like GetInstitutionQuarterlyActivity.

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?

Ends with concrete intended-use guidance ('Use this to answer what's the consensus 13F move this quarter?') and each bucket's meaning steers selection. However, it never names an alternative tool or states when NOT to use it, so it stops short of full when/when-not routing.

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