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

With no annotations, the description carries the burden: it discloses the computation exactly and adds cost/access context ('5 free trial calls per signed wallet'), which tells the agent about payment/auth. However it says nothing about return format, handling of empty or single-element input, or error behavior.

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 tight sentences with the definition front-loaded and the input hint immediately after. The emoji/pricing tail is promotional but short and informative about cost.

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 one-parameter pure calculator with no output schema, the description covers what is computed and what to supply. The remaining gap is the string-versus-array serialization ambiguity, which is the one thing an agent could get wrong.

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% for the single 'values' parameter, so any description help matters. 'Provide values array' clarifies the intended content, but it conflicts in spirit with the schema type of string (no indication of whether values are comma-separated, space-separated, or JSON-encoded), leaving the actual encoding ambiguous.

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 ('Calculate the midrange of a dataset') and even defines the operation ('the average of its minimum and maximum'), which lets an agent separate it from median/mean/mode siblings without opening the schema. It does not name an alternative explicitly, keeping it at 4 rather than 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?

'Provide values array' is an input instruction, not usage guidance. There is no statement of when to prefer midrange over x402-range-stat, x402-median, or x402-midhinge, and no prerequisites beyond the pricing line.

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