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

Annotations already declare the safe read profile (readOnly, idempotent, non-destructive, openWorld), so credit goes to what the description adds: units in integer USD millions, a fixed (non-arbitrary) monthly window, snapshot vintage, hashes, methodology caveats, and the primary-vs-comparison default. The pagination bounds are conveyed by the schema rather than the description, keeping this just short of 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?

A question front-loads the purpose and the second sentence packs return shape plus the one conditional parameter. It is dense but every clause carries information; only slight compression would improve it.

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 carries the return-value burden and does so competently (units, month, series identity, line references, vintage, hashes, caveats). Routing to sibling tools and explicit alternatives remain the only meaningful gaps.

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, but the description adds real semantic value beyond the schema: holdings are integer USD millions, the window is fixed monthly, and the comparison series are 'duplicate benchmark-break comparison columns' used only for historical breaks, sharpening the schema's vaguer wording.

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?

It states a specific verb+resource with scope: one holder's U.S. Treasury holdings over a monthly window. That is clear, but the description never names the sibling tools (compare_holders, rank_holders, official_share) it must be distinguished from, so the agent must infer the difference from the name and schema alone.

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 guidance is limited to parameter-level routing: 'set include_comparison_series only to inspect duplicate benchmark-break comparison columns.' There is no when-to-use-this-vs-alternatives guidance; the useful pointer to treasury_tic_find_holders lives in the schema, not the description.

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