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

Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, and the description's hints about the 'full outstanding and priced universe' mostly restate what the schema already says (hundreds of rows for 'outstanding'). It adds the default-day semantics implicitly via 'omit the date for the most recent day with prices', but nothing about ordering, pagination, or gaps on days with no prices.

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 verb and resource, then a single colon-delimited list of modes; no filler sentences. The one long sentence is dense and could be split for readability, but every clause carries information.

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 three optional parameters, a fully documented schema, and no output schema, the description covers what the tool returns at a conceptual level (on-the-run by tenor, full universe, priced CUSIPs) and the default date behavior. It is nearly complete; only result ordering/shape detail is absent, which is minor for a read-only listing tool.

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 goes further by mapping each enum option to a user-facing intent ('which security is on-the-run for each tenor', 'the full outstanding and priced universe', 'just the priced CUSIPs'), which helps an agent translate a request into the right include values. It does not expand on the auction-vs-issue distinction, which the schema handles well.

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 and resource ('List Treasury securities as at a date') and then enumerates the three distinct result modes: on-the-run per tenor, full outstanding universe, or priced CUSIPs only. The parenthetical about resolving 'the current 10-year' to a CUSIP makes it unmistakably distinct from the singular get_treasury_security and from price_treasury_security.

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 clear usage context, notably the concrete task of resolving a tenor reference to a CUSIP, and tells the agent how to handle the omitted-date case. It stops short of naming siblings as alternatives (e.g., use get_treasury_security for a single CUSIP), so there are no explicit exclusions to complete the routing picture.

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