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

Annotations already cover safety (readOnly, idempotent, non-destructive, non-open-world), yet the description adds substantial non-obvious behavior: a 404 OWNERSHIP_SECURITY_NOT_FOUND on unknown securities, credit costs (30/page flat, 40 grouped, 404 still charged), and that grouped mode is unpaged. These are the kind of cost/error/mode traits an agent cannot derive from structured fields.

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 and anchoring constraint are front-loaded, then modes, then cost/endpoint. It is dense but nearly every clause carries information; the trailing EDGAR-index sentence is partially tangential and the run-on paragraph structure makes it harder to scan.

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 10-parameter tool with no output schema, the description covers anchoring, error behavior, the securities block, per-row additions, the grouped aggregation shape, pagination, cost and endpoint. Only the mapping of the remaining sort_by/sort_order/paging params to returned ordering is left implicit, which is minor.

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%, so the schema already documents all ten parameters, including the YYYYQn quarter format, the activity enum values, and the ticker-matches-multiple-CUSIPs case. The description restates these and adds only the framing that quarter/type/activity/sort_by 'narrow' the rows, which is marginal beyond the schema baseline.

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 verb+resource: 'One security's 13F holder rows across managers, anchored by exactly one of cusip / ticker.' It also distinguishes itself from get_institutional_portfolio by describing its rows as the same detail rows plus manager_cik / manager_name, so an agent can tell the two apart 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?

The description gives the selection rule for its own modes (flat default vs group_by_quarter=true) and a precondition (exactly one of cusip / ticker), but it never routes the agent between this tool and the closely related sibling search_institutional_holdings, nor states when a grouped aggregate is preferable to detail rows. Usage is implied by parameter behavior rather than stated.

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