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

Annotations already establish that this is read-only, idempotent, and non-destructive, so the description only needs to add behavioral context. It does add useful context by stating the data is monthly and optionally filterable by security description, but it does not disclose default limits, date-range behavior, or return structure.

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?

The description is two concise sentences with no filler. The core subject is front-loaded, the optional filter is stated plainly, and every sentence contributes meaningful 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?

For a simple read-only tool with two optional parameters and full schema coverage, the description allows a basic call to be made correctly. However, with no output schema, it does not clarify the return format, default row count, or how far back the monthly history goes, which leaves some practical ambiguity.

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 both 'limit' and 'security'. The description reinforces the security parameter by naming Treasury Bills, Notes, Bonds, and TIPS, but it adds nothing about the 'limit' parameter beyond what the schema provides. This matches the baseline for fully documented parameters.

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?

The description clearly identifies the resource: average interest rates on US Treasury marketable and non-marketable securities, broken down by month. It is distinct enough from siblings like treasury_exchange_rates, though it lacks an explicit verb such as 'Returns' and does not directly contrast itself with any sibling.

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 no guidance on when to choose this tool over related siblings such as treasury_auctions, treasury_exchange_rates, or treasury_debt. There is no conditional context, no exclusions, and no mention of alternatives, leaving the selection decision entirely to the agent.

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