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

With no annotations, the description carries the full burden and does substantial work: it discloses the weekend/holiday fallback to the prior business day, the default-to-latest behavior, the output contents, and the x402 payment cost and chains. It omits rate limits, caching or failure behavior, which keeps it short of a 5.

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 use case, then Input/Output in compressed labels, then the fallback rule, then a concrete example and price. Every clause carries information, though the Price/example tail reads as appended boilerplate rather than part of the core 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?

For a zero-required-parameter read tool with no output schema, the description supplies input formats, defaults, the business-day fallback, and the shape of the returned JSON, which is what an agent needs to call it and interpret results. Only operational details such as error or payment-failure handling are missing.

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. The description adds the date format (YYYY-MM-DD) and, usefully, the 1-366 bound on days that the schema does not state, but otherwise mirrors what the schema already documents.

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+resource: the official US Treasury par yield curve for a day or a recent stretch, with named tenors (1m-30y), derived spreads (2s10s, 3m10y), inversion flags and history. An agent can distinguish this from adjacent siblings such as us_macro_series or fx_rates without opening the schema.

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?

"Use when an agent needs the official US Treasury par yield curve for a day or a recent stretch" gives a clear triggering condition. It stops short of naming when NOT to use it or pointing to an alternative (e.g. us_macro_series for non-yield-curve macro data), so routing is implied rather than resolved.

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