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

No annotations are provided, so the description carries the full behavioral burden. It discloses the billing/auth trait ('5 free trial calls per signed wallet'), which is genuinely useful, but says nothing about required inputs, error behavior, units, rounding, or what the result looks like for a financial calculation.

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?

One front-loaded sentence delivers the definition and formula with no filler; the trailing free-trial note is short and informative. Slightly busy with the emoji, but efficient overall.

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 two-input calculator with no output schema, the formula largely covers the return value and both parameters are at least implicitly explained. The remaining gap is that both params are marked optional with no format guidance, so an agent could call it with missing or mis-scaled inputs and get a silently wrong number.

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 0%, so the description must compensate. It does partially: 'coupon rate divided by price, multiplied by 100' tells the agent what each parameter contributes and that the output is a percentage. It still omits input format (percent vs. decimal, e.g. 5 or 0.05), which is the highest-risk ambiguity for a yield calculator.

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?

It states a specific verb and resource ('Computes current yield') and even spells out the formula (coupon rate / price × 100), which lets an agent separate it from pure-number tools. However it never distinguishes itself from close siblings like x402-bond-yield, x402-percent-yield, or x402-yield-to-maturity, so routing between them remains guesswork.

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?

There is no when-to-use, when-not-to-use, or alternative guidance. The only contextual statement is the free-trial quota, which is about payment, not about selecting this tool over a sibling yield calculator.

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