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

Annotations already declare this a pure, read-only, idempotent, non-destructive operation, so the safety burden is met. The description adds the valuable trait that evaluation is exact (avoiding float drift) and that no mental math should be trusted, but does not say how a malformed expression is 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?

Three tight sentences: capability, grammar, then the usage imperative. The directive to use it is front-loaded after the capability, and no sentence is filler.

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, no-output-schema tool this is nearly complete: purpose, syntax, and usage pressure are all present. The only omission is what is returned (a value/error) and a concrete expression example, which would remove the last ambiguity.

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?

With 0% schema description coverage, the description must carry the parameter meaning, and it does: it specifies the grammar (+ - * / parentheses, min, max, round, abs, sum of a list). It stops short of showing exact call syntax, e.g. how a list is delimited for sum, leaving a small inference gap.

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 (evaluate) and resource (an arithmetic expression) and enumerates supported operators/functions, so the agent knows exactly what this tool computes. It is unmistakably distinct from every sibling, which are all invoice/vendor/bank workflow tools.

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?

Gives an explicit directive with conditions: 'Use it for every amount you derive' and 'Never do arithmetic in your head,' plus concrete example cases (variances, min(invoiced, received) x price, tax, pair sums). No alternative could be confused here, so the absence of a named sibling alternative is not a gap.

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