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 algorithm (the operation itself is the behavior for a pure calculator) and a quota constraint ('5 free trial calls per signed wallet'), which is genuine access-related context. It says nothing about division-by-zero handling, output format/precision, or whether the call is a paid x402 invocation beyond the trial.

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 functional content is one front-loaded clause with zero wasted words. The appended promotional sentence and emoji are marginally useful (quota info) but sit awkwardly at the end of a math 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 trivial two-input calculator with no output schema, the description is close to sufficient because the formula implies the return value (a percentage). Gaps remain around input encoding (strings) and the fact that the schema marks zero parameters as required even though both are mathematically necessary.

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 clarify the semantic role of each parameter by mapping them into the formula (actualYield is the numerator, theoreticalYield the denominator). However, it does not specify expected format or units — the schema types are strings, so it is unclear whether inputs are plain numbers, percentages, or strings needing parsing.

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?

Names a specific resource ('Percent Yield') and states the exact computation, including the formula 'actual yield divided by theoretical yield, times 100'. That is far more precise than a tautology. It does not, however, differentiate itself from nearby siblings such as x402-yield-to-maturity, x402-current-yield, x402-earnings-yield, or x402-percent-composition.

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 guidance on when to use this tool versus the many other yield/percentage siblings, no prerequisites, and no exclusions. The only contextual sentence is a promotional note about free trial calls, which does not help an agent choose this tool.

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