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

Beyond the readOnly/openWorld annotations, the description discloses non-obvious behavior: weekend/holiday requests fall back to the previous business day, the source is named in every answer, HTTP 400 is returned before payment on bad input, outages are not charged, and the exact price is 0.002 USDC via x402. These are billing and error semantics an agent cannot infer from annotations or schema.

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?

It is front-loaded with the trigger condition and then layers data scope, fallback behavior, error handling, and price, with no filler sentences. The main text is a single dense run-on with stacked parentheticals, which costs it the top mark on readability.

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 one-parameter, annotation-light tool with no output schema, it covers everything needed to call correctly: data range, default behavior, holiday fallback, where the source attribution appears, failure semantics, and cost. Nothing an agent needs before invoking it is 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 schema already documents the single date parameter and its 1990-01-02 floor. The description adds meaning the schema does not: the default is the latest published curve, and weekend/holiday dates resolve to the previous business day, which materially changes what a caller should expect to receive.

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 verb and resource: 'official US Treasury daily par yield curve, 1 month to 30 years.' It scopes the data precisely (10Y-2Y and 10Y-3M spreads, risk-free rate, discounting) so an agent can tell it apart from fx_rates or inflation 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?

The leading 'Use when an agent needs US government bond yields, a risk-free rate or the yield curve' gives explicit trigger conditions with concrete examples (spread, recession signal, discounting). It stops short of naming a sibling as the alternative or stating when NOT to use it, so it lands just below the top mark.

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