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

Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, so the safety profile is covered. The description adds genuine context on top: default inclusion set, the meaning of omitting the date, and non-trading-day behavior. Auth requirements and response size/pagination are not discussed, but they are minor for a read-only curve lookup.

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?

Two front-loaded sentences carry the payload, with the caveat sentence placed last. Every clause does work: scope, optional outputs, default behavior, and a domain disambiguation.

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 zero-required-parameter read tool with no output schema, the description tells an agent what comes back and how defaults behave, which is sufficient to call it correctly. The one real hole is the mismatch between the advertised par/money-market curves and the include enum, which leaves the agent uncertain how to request them.

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% and the schema descriptions already explain the date format, the default include set, and every enum value, so the baseline is 3. The description adds little beyond restating those fields, and it introduces a discrepancy: it advertises a 'par curve' and 'money-market curve' on request, but neither appears in the include enum, which could send an agent looking for options that do not exist.

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 (get the U.S. Treasury yield curve) plus the exact scope (a single day) and enumerates the curve variants returned. The single-day framing implicitly separates it from get_treasury_rate_history, and the closing note 'Treasury yields are not mortgage rates' pins the domain against mortgage-related siblings.

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 concrete when-to guidance: 'Omit the date for the most recent published day, which is what you want on a weekend or holiday.' It does not name sibling tools or state exclusions (e.g., when to reach for history or a specific security instead), so it stops short of full routing guidance.

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