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

With no annotations, the description carries the full behavioral burden. It does disclose a real access constraint ('5 free trial calls per signed wallet'), which is the kind of auth/rate-limit context the rubric credits, but it omits validation behavior (e.g., whether the triangle inequality is enforced or how invalid side lengths are handled).

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?

Two short sentences with the purpose front-loaded ahead of the promotional trial note. No filler sentences, though the emoji/pricing tail is slightly extraneous to the tool's function.

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 three-input arithmetic tool with no output schema, the description covers the core computation but leaves gaps: output format, handling of degenerate/non-triangle inputs, and whether values are numeric strings. Adequate but not fully 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 coverage is 0% and the three parameters are bare single letters 'a', 'b', 'c' typed as strings. The phrase 'from its three side lengths' partially compensates by mapping the three inputs to side lengths, but it gives no units, ordering, numeric format, or constraint info, so the compensation is only marginal.

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 states a specific verb and resource ('Returns a triangle's perimeter') and names the inputs ('three side lengths'), which cleanly separates it from siblings such as x402-triangle-area, x402-triangle-heron, and x402-trapezoid-perimeter. An agent can identify the operation without opening the schema.

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?

Usage is only implied by the purpose statement; there is no explicit when-to-use, when-not, or named alternative (e.g., triangle-heron for area from sides). The trailing trial-call note is pricing information, not selection guidance. Mirrors the calibration case that scored 2 for having no when-to-use guidance.

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