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

No annotations are provided, so the description carries the full burden. It does usefully disclose the payment/auth model ('5 free trial calls per signed wallet'), which tells the agent a signed wallet is required and that usage is metered. It says nothing about output format, rounding, zero-revenue handling, or negative operating income after the formula.

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?

A single front-loaded sentence states the operation and formula immediately; no wasted prose. The trailing promo line ('🆓 5 free trial calls per signed wallet') adds slight noise but carries genuine payment information.

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 low-complexity two-input calculator with no output schema, the description covers what is computed and the payment model, which is close to sufficient. It still leaves input formatting, requiredness, and result format (percent vs. ratio) unspecified, gaps neither the schema nor annotations fill.

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. The formula explicitly names both inputs ('operating income divided by revenue'), giving each parameter clear meaning, but it omits that both are typed as strings, whether currency symbols or units are allowed, and whether the inputs are required (required count is 0).

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 and gives the exact formula ('operating income divided by revenue, times 100'), which is more precise than the name alone. It does not, however, explicitly distinguish itself from close siblings such as x402-gross-margin, x402-profit-margin, or x402-margin-calc, so an agent must infer the difference from the formula.

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 conditions, and no mention of the alternative margin tools that populate the sibling list. The agent must deduce on its own that this is the 'operating income' variant rather than gross or net margin.

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