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

Annotations already declare readOnly=true, idempotent=true, destructive=false and closed-world, so the safety profile is fully covered. The description adds nothing beyond that: no formulas (e.g. whether LTV uses gross margin and churn), no rounding/unit handling, no behaviour on degenerate inputs such as very high churn. Adequate but not value-adding.

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 that names the tool's outputs before its inputs, with no filler or redundant restatement of the title.

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 stateless calculator with no output schema, the description correctly enumerates the returned metrics, which is the key missing piece an agent needs. The remaining gap is methodological: the exact LTV and payback formulas are unspecified, so an agent cannot predict edge-case output values.

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%, so all six parameters are already documented with units, ranges and examples. The description's phrase 'from spend, new customers, revenue per customer, gross margin and churn' merely restates the parameter set and adds no semantic detail such as period alignment between spend and new customers.

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?

Specific verb plus an explicit enumeration of the four metrics produced (CAC, LTV, LTV:CAC, CAC payback in months), which is far more concrete than the title alone. It is implicitly separable from siblings like customer_lifetime_value and max_affordable_cac because it bundles all four metrics from one input set, but it never states that distinction.

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?

Usage is only implied by the nature of the tool: an agent infers it is for computing unit economics from a spend/customer/ARPU/margin/churn snapshot. There is no statement of when to prefer it over customer_lifetime_value or max_affordable_cac, no prerequisites, and no exclusions.

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