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

With no annotations, the description carries the full behavioral burden, but it does disclose two useful traits beyond the schema: the result is rounded to two decimals and the call is metered ('5 free trial calls per signed wallet'). It does not state the underlying convention (Fisher vs simple nominal minus inflation) or what happens on exhausted quota, so key behavioral ambiguity remains.

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 conveys the operation, inputs, and output precision, followed by a short billing tagline. Nothing is redundant, though the emoji/pricing clause is marketing rather than functional.

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 pure calculator with no output schema, the description covers the essentials and output rounding. The gaps are the input format (percent vs decimal) and the exact formula convention, which matter for correct invocation of a finance calculation but are omitted.

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 0% (both parameters are bare strings with no descriptions), so the description must compensate. It does map 'nominal rate' to nominal and 'inflation' to inflation, which is more than the schema provides, but it gives no unit/format convention (decimal fraction vs percent) despite both params being typed as strings.

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 and resource ('Computes the real interest rate') and names both inputs (nominal rate, inflation), so the agent knows exactly what it produces. It does not differentiate itself from adjacent siblings like x402-simple-interest or x402-inflation-adj, which would require the agent to read further to disambiguate.

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 guidance, no mention of alternatives (e.g., inflation-adjustment or nominal-rate helpers among the many siblings), and no stated prerequisites. The only contextual hint is the free-trial note, which is billing, not usage.

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