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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false, and openWorldHint=false, so the safety profile is fully covered. The description adds no behavioral context of its own — no edge-case handling (e.g., zero spend/zero margin), no units assumptions beyond margin percent, no note on output 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 lists the outputs immediately, followed by a link. It is efficient; the external URL is the only non-earning element for an agent.

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 pure-function calculator with a fully described 3-param schema and complete safety annotations, the essentials are covered. However, it omits any handling notes for degenerate inputs and offers no differentiation from numerically adjacent siblings, leaving small but real gaps.

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 100% with all three parameters documented, so the baseline is 3. The description restates the inputs (ad revenue, ad spend, gross margin) but adds no syntax, range, or unit detail beyond what the schema already provides.

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 (Calculate) and enumerates concrete outputs (ROAS, ACOS, break-even ROAS, profit), so the agent knows exactly what the tool produces. It does not explicitly distinguish itself from a sibling like roas_to_mer_converter, which is the only gap.

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 description never says when to use this tool versus alternatives (e.g., roas_to_mer_converter, ltv_cac_calculator) or what preconditions apply. The only extra guidance is a link to a 'full version', which is promotional rather than situational.

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