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 disclose billing behavior (5 free trial calls per signed wallet), which is genuine context beyond structured fields, but says nothing about what happens with invalid/non-triangle side lengths, unit expectations, or output shape.

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 functional sentence followed by a short billing note; no filler or redundancy. The emoji/promo adds mild noise but does not obscure the purpose.

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 pure-computation tool with no output schema and no annotations, the description covers purpose, high-level inputs, and cost. It still leaves gaps on input validation, units, and result format that a caller might reasonably want.

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. 'Three side lengths' tells the agent the semantic role of all three params, which is real value over bare 'a','b','c', but it does not map which param is which, note that they are strings, or specify units/format.

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 ('Returns a triangle's circumradius') plus the input basis ('from its three side lengths'), which is more than a restatement of the name. It is distinguishable from nearby siblings like x402-triangle-inradius and x402-triangle-area by the named output, but it never explicitly contrasts with them.

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 mention of the closely related triangle tools (inradius, area, heron, perimeter), and no note on prerequisites such as the sides needing to form a valid triangle. The only extra sentence is a pricing promo, not usage direction.

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