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 structurally. The description adds the input-to-output mapping (spend + leads + convPct → CPL/customers/CPA), but says nothing about the formula used, rounding, units, or edge cases like zero leads.

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 core sentence is well-formed and front-loaded, but the trailing marketing link to an external site consumes space without helping an agent decide or invoke the tool. Roughly half the text is actionable.

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?

With no output schema, the description does name the three computed results, which gives some return-value signal. It stops short of describing result structure, units, or failure behavior for a tool with three required numeric inputs.

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 coverage is 100% with all three parameters documented in the schema, so the baseline is 3. The description does clarify that convPct is a lead-to-customer conversion rate, which mirrors the schema rather than extending it, and adds no format or unit guidance beyond that.

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 names the exact outputs (cost per lead, expected customers, cost per acquisition) plus the three inputs that produce them. It does not, however, differentiate itself from adjacent siblings such as ltv_cac_calculator, cpa_to_cac_scalability_matrix, or roas_calculator, so an agent must infer which one 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 prerequisites, and no mention of alternative tools. The only routing hint is the sibling list itself, which the description does not exploit.

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