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

No annotations exist, so the description carries the full burden. It usefully discloses the actual computation and a trial/payment constraint ('5 free trial calls per signed wallet'), but says nothing about units, input format, permissions, or error behavior for a numeric tool.

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's identity and formula in a single tight sentence. The trial-call marketing snippet and emoji add slight noise but are short and relevant to invocation.

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-parameter calculator the purpose and formula are covered, and no output schema exists so return values need not be documented. However, with 0% schema coverage and no annotations, the absence of units/format and success/error behavior leaves it only minimally complete.

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 does map elementMass and compoundMass to their roles, which is genuine added meaning, but it gives no format or units guidance for the string-typed inputs, leaving half the semantics open.

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 ('Computes') and resource ('percent composition') and even gives the exact formula (element mass / compound mass × 100), so the purpose is unambiguous. It does not distinguish itself from the many percent-related siblings (x402-percent-of, x402-percent-of-value, x402-percentage-of, x402-concentration), so it falls short of a 5.

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 explicit when-to-use or when-not-to-use guidance and no alternatives named, despite a crowded field of percent/concentration siblings that could easily be confused with this one. Usage is only faintly implied by the formula.

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