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

No annotations exist, so the description carries the full behavioral burden. It discloses the paid-access model ('5 free trial calls per signed wallet'), which is genuinely useful, but says nothing about what happens when old is zero, whether the result is a fraction or a percent-scaled number, or the returned format.

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?

A single front-loaded sentence stating the operation, followed by the access note. Little waste, though the trial-call promo and emoji are marketing noise rather than invocation guidance.

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 4-parameter numeric tool with zero annotation coverage, no output schema, and no sibling disambiguation, the description is thin. Edge cases (old = 0, negative values), required input pairing, and output units are all left unaddressed.

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% across 4 parameters, and none are marked required. The description partially compensates by clarifying that 'current' and 'previous' are aliases for 'new' and 'old', which is real semantic value. It still does not state which pair must be supplied or how conflicts between the two pairs are resolved.

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+resource: computes percentage change between old and new values. That is clear enough to act on. However, it does no work to distinguish itself from close siblings such as x402-percent-change-of, x402-percent-change-array, x402-rate-of-change, and x402-percent, leaving the agent to guess which percent tool applies.

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 exclusions, and no named alternative. The mention of 'current and previous aliases' hints that the tool is flexible about input naming but does not tell the agent when to pick this over the many sibling percent/change tools.

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