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

No annotations, so the description carries the full behavioral burden. It discloses the payment model ('5 free trial calls per signed wallet'), which is genuinely useful, but says nothing about the return format, rounding/precision, or whether the conversion is metric tonne vs short/long ton — a real ambiguity for a unit converter.

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?

Very short and front-loaded with the conversion purpose, followed by a single pricing note. No filler, though the conversion description is arguably too terse for the ambiguity involved.

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 simple one-parameter converter this could be sufficient, but with no annotations, no output schema, and no schema descriptions, the description leaves the unit definition and input format unresolved. It needs one more sentence covering input format and which ton is used.

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?

There is one parameter, 'value', typed only as string with 0% schema description coverage. The description adds no meaning: it doesn't say whether the input is a numeric string, whether units or commas are allowed, or how invalid input is handled.

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?

Names a specific verb and resource ('Convert kg to tons'), which is unambiguous enough to distinguish it from most siblings. It does not acknowledge the direction-inverse sibling x402-tons-to-kg, but that sibling is named in a self-explanatory way, so the agent can still route correctly.

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 or when-not-to-use guidance. The description never mentions the reverse tool (x402-tons-to-kg) or the general x402-units-convert, and gives no hint about which unit system ('tons') is intended. Only the tool name implies direction.

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