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

No annotations exist, so the description carries the full burden, but it does disclose a genuine behavioral trait: the total=0 edge case returns 0 rather than erroring. It also notes the free-trial/payment model. It does not state what happens with non-numeric or malformed string inputs, which matters because both parameters are typed as strings.

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?

Front-loaded with the tool name and formula in a single compact sentence, with the edge case immediately after. The pricing/emoji tail is boilerplate clutter but does not obscure the core specification.

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 stateless two-parameter calculator with no output schema, the definition supplies the formula and the singular edge case, which is most of what an agent needs. The remaining gap is return shape (raw number vs formatted string) and input validation behavior.

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 schema gives only names and types. The description partly compensates by assigning roles (value is the numerator, total is the denominator), which the schema does not convey. It still says nothing about expected string formats, numeric range, or whether values may exceed the total.

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 names a specific computation and pins down the exact formula: value divided by total times 100. That is much sharper than a tautology like 'computes progress percent'. It does not, however, distinguish itself from the many sibling percent tools (x402-percent-of, x402-percent-change-of, x402-percent-composition), so an agent cannot tell from the description alone which percent tool applies.

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 prerequisites, and no mention of alternatives. Given dozens of near-identical percent siblings, a sentence such as 'use for progress bars / completion ratios, not for change between two values' would be the highest-value addition here, and it is absent.

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