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

With no annotations, the description itself usefully discloses that expressions are evaluated in a safe/sandboxed way and that each signed wallet gets only 5 free trial calls, an auth need and rate limit. It stops short of describing return shape or post-trial behavior, but for a simple evaluator these are meaningful behavioral disclosures.

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 description is a compact two-part sentence with no padding; the trial note is useful. Slight redundancy ('Math:' alongside the x402-math name) prevents a 5.

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 tool with three ambiguous optional parameters and no output schema, the description is incomplete: it omits expression syntax, which parameter to pass, expected return value, and error behavior. The safety and wallet-trial context is helpful but not sufficient for reliable invocation.

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?

All three parameters have only tautological descriptions ('Q to process', 'Expr to process', 'Expression to process'), and none are required, so an agent cannot tell whether to use q, expr, or expression or whether they are aliases. The tool description does not add any parameter-level guidance.

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?

Description is a noun phrase ('Math: Safe math expressions.') with no explicit action verb, so an agent must infer that the tool evaluates or processes expressions. It names the math domain but does not distinguish generic x402-math from the hundreds of math siblings like x402-nroot or x402-arithmetic-series-sum.

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?

No guidance is given on when to choose this tool over sibling math/computation tools. The trial-call note is a billing constraint, not a usage rule, and no alternatives or exclusions are mentioned.

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