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

Annotations already declare readOnly/not-destructive/closed-world, and the description goes well beyond them: it discloses the delta methodology, that entries/exits require observed filings in both quarters, the CIK-successor and multi-CIK exclusion handling, partial coverage during an open filing window, and the markdown two-section return shape. This is rich behavioral context that annotations alone cannot convey.

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?

Purpose is front-loaded in the first sentence before the edge-case caveats, and the trailing sentences carry real information about exclusions. The opening sentence is very long and clause-heavy, but nearly every clause earns its place given the methodology being described.

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, so the description carries the return-format burden and does so ('returns a markdown table with two sections'), plus it explains counts/shares of excluded filers and partial-window coverage. For a non-trivial 13F analytics tool, an agent has everything needed to call and interpret it.

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 description coverage is 100% (ticker, maxResults with clamp/default, reportDate with snap behavior), so the schema carries parameter meaning. The description reinforces the quarter-over-quarter report-date concept but adds no syntax or format detail beyond the schema, matching the baseline 3.

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 institutions with biggest absolute share additions/reductions on a stock this quarter, versus the previous 13F report date). The scope is unambiguous and an agent won't confuse it with holding-history tools. It does not explicitly name or differentiate itself from likely siblings such as GetInstitutionQuarterlyActivity or GetMarketWide13FActivity, so it stops short of a 5.

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 closing sentence ('Use this to surface the most actionable quarterly signal from 13F filings') implies when the tool is appropriate, and the body explains which situations are covered (open filing window, missing filings). But it never names an alternative tool or states when NOT to use it, leaving selection to inference.

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