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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, openWorldHint=false, so the agent knows this is a safe, deterministic, offline computation. The description adds some value by implying two outputs (expansion ARR and the equivalent new-logo CAC), but says nothing about return format or precision. With annotations covering the safety profile, a 3 is appropriate.

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 first sentence is well front-loaded and efficiently describes the calculation. The second sentence is a marketing URL that does not help an agent select or invoke the tool, so it does not fully earn its place.

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 read-only deterministic calculator with four fully documented required parameters and clear annotations, the description is adequate. The gaps are the absent output description (no output schema) and no guidance on units/scale of the computed result, which leaves the agent slightly short of complete.

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 four parameters (existingCustomers, adoptionRatePct, upsellAcv, newLogoCac) are already documented by the schema. The description adds only the framing of upsell ACV versus new-logo CAC comparison, which is marginal over the schema. Baseline 3 applies.

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: 'Estimate expansion ARR from an upsell offer and the new-logo CAC it would take to buy the same growth.' That is far more informative than a restated title. However, it does not distinguish itself from close siblings such as customer_expansion_revenue_matrix or ltv_growth_multiplier_simulator, all of which are expansion/growth models.

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 statement of when to use this tool versus any alternative, no prerequisites, and no mention of siblings. The only secondary sentence is a promotional link to a web calculator, which gives no invocation guidance.

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