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

Annotations already declare readOnlyHint and openWorldHint. The description adds valuable behavioral context beyond the annotations: the exact pricing model ($0.005 per successful call via x402) and the free tier (5 free calls/day across all tools), which are not in the annotations. It also mentions the data range and history limit, though it does not describe rate limits beyond the free tier.

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 a single well-structured sentence followed by a pricing sentence. It is front-loaded with the core purpose and then adds pricing. It could be slightly more concise, but every element serves a purpose.

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?

Given no output schema, the description covers the data range, date handling, history option, and pricing. It is nearly complete for an agent to call the tool correctly, though it could clarify the response format or the exact rate-limiting behavior beyond the free tier.

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 parameters are fully documented in the schema. The description mentions 'latest or a given date' and 'optional daily history for one tenor,' which aligns with the parameters but adds no new semantic detail beyond what the schema provides. 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?

The description names a specific resource (official daily US Treasury par yield curve) and scope (1M to 30Y, percent, latest or given date), plus optional history. It clearly distinguishes itself from siblings like fx_rates and macro_series by focusing on Treasury yields.

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?

It implies usage through context (latest or a given date, optional history for one tenor) but does not explicitly state when to prefer this over fx_rates or macro_series, nor when-not to use it. The pricing note provides some context but not selection guidance.

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