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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered; the description adds genuinely useful context that the annotations don't—a 5-credit cost and a production-billing requirement. However, it never says whether margin is returned as a percentage or a dollar amount, nor the formula used, which matters for interpreting a numeric result.

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 short sentences with no waste, and the core action is front-loaded ahead of the billing caveat. Tight and readable, though the billing note could be more clearly separated from the functional description.

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 simple two-parameter, read-only calculator with no output schema, the definition covers the action and access cost but not the shape or units of the result. That omission is the main completeness gap for an agent that needs to use the returned value.

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%, so the description must carry the burden, and it only maps the two parameters to "price" and "direct cost." It doesn't say whether price is per-call, per-unit, or per-period, nor what counts as a "direct cost," leaving ambiguity a caller must resolve.

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 gross margin" from "price and direct cost." This clearly distinguishes it from the sibling tools, none of which cover unit economics, though the description doesn't explicitly name an alternative.

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?

The only usage guidance is an access constraint ("PAID ONLY: 5 prepaid credits; production billing required"), which tells the agent a precondition but not when to choose this tool or when not to. No alternatives or scope conditions are given.

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