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

With no annotations and no output schema, the description carries the full behavioral burden. It discloses the payment model ('5 free trial calls per signed wallet'), which is useful non-obvious context, but says nothing about the return value, determinism, or validation behavior.

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 naming the computation and its inputs, followed by a short billing qualifier. No filler, though the emoji adds minor noise.

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 numeric pricing tool with 0% schema coverage, no annotations, no output schema, and zero required params, the description leaves the agent unable to determine valid value ranges, units, or whether all inputs are truly optional. The alias hints help, but a Black-Scholes calculator needs unit/format clarity to be called correctly.

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% and all 7 params are bare strings, but the description compensates by clarifying the two alias pairs ('spot or price', 'volatility or sigma'), which an agent could not infer from the schema alone. It still omits critical semantics like units for time (years vs days) and whether rate is a decimal or percent, so compensation is partial.

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 states a specific verb ('Computes') and resource ('Black-Scholes call price') and enumerates the pricing inputs, which clearly separates it from the sibling x402-black-scholes-put. It does not, however, explicitly call out the put sibling or scope the tool beyond what the name already conveys.

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?

No when-to-use guidance, no alternatives, no preconditions (e.g. positive time to expiry). The only contextual note is the free-trial/payment line, which is billing information rather than usage routing.

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