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

With no annotations, the description carries the full burden. It usefully discloses the computation formula and the pricing/trial behavior ('5 free trial calls per signed wallet'), which is real behavioral context. It does not state output units precisely beyond 'percentage', whether start=0 is handled, or what happens after the trial.

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?

The purpose and formula are front-loaded in one tight sentence; little waste. The trailing emoji promo is slightly noisy but does not obscure the core meaning.

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 two-parameter arithmetic utility with no output schema, the description covers what is computed (percent return), how (formula), and cost model. Missing edge-case handling is minor for a tool this simple.

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%, so the description must compensate. It does establish the roles of 'start value' and 'end value' relative to the formula, but says nothing about input format (schema types are bare strings), numeric parsing, or the zero-start constraint implied by division.

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 ('percentage return'), and spells out the exact formula ((end-start)/start), which is unambiguous. However, it never differentiates itself from near-identical siblings such as x402-percentage-change, x402-returns, or x402-annualized-return, leaving the agent to infer the distinction.

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 conditions, and no mention of alternatives among the many return/percentage siblings. The only non-purpose sentence is a promotional note about free trial calls, which does not help tool selection.

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