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 without description help. The description's only behavioral addition is the compounding-inflation model, which is useful context but not a disclosure of assumptions, edge cases, or how the projection behaves when CPA is already above the max.

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-formed and front-loads the purpose, but the second sentence is a marketing link that does not help an agent decide or invoke the tool. Roughly half the description is non-functional for the caller.

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 3-parameter numeric calculator with no output schema, the description should say what comes back (a month count, a boolean crossover flag, or 'never' when inflation is zero/negative). It leaves the return shape and the compounding assumption implicit, which is a real gap even though the tool itself is simple.

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 three parameters are already documented in the schema, establishing the baseline of 3. The description adds no format, unit, or range detail (e.g., percentage as 5 vs 0.05) beyond what the schema 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?

The description states a specific computation: projecting how many months until compounding CPA inflation crosses a max viable CPA. That verb+resource pairing is clear and distinguishable from siblings like cpa_to_cac_scalability_matrix or ad_creative_fatigue_forecaster, but it never explicitly names or rules out any sibling, which keeps it short of a 5.

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 the many other CPA/unit-economics calculators, no prerequisites, and no exclusions. The only extra sentence points to an external web page, which is promotional rather than guidance.

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