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

Annotations already declare read-only, idempotent, open-world semantics, so the safety profile is covered. The description adds genuinely useful interpretation guardrails — that a fail-to-deliver is a settlement failure and explicitly NOT evidence of naked short selling — which prevents a common misreading of the returned data.

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-loads the core purpose in the first clause, then return fields, then the caveat. Every sentence contributes, though the naked-short-selling disclaimer is somewhat lengthy for a tool definition.

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 compensates by enumerating the returned fields (ticker, security description, settlement date, shares failed, price), the data source, the ranking metric, and the default period behavior — everything needed to call and interpret the result.

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 limit range/default and the YYYYMM+a/b period format are already documented in the schema. The description adds no parameter-level detail beyond pointing at ftd_periods, so the 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?

States a specific resource (largest fails-to-deliver per SEC reporting period), the ranking basis (share count), and the data source (CNS fails-to-deliver file). It is clearly distinguishable from siblings ftd_periods (period enumeration) and ftd_security (per-security lookup).

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?

Gives a clear context question it answers ("which stocks had the most failed deliveries this period") and routes the agent to ftd_periods for valid period values, plus the default behavior when period is omitted. It does not explicitly contrast when to prefer this over ftd_security, so it stops short of full when/when-not guidance.

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