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

Annotations already declare readOnlyHint, non-destructive, and closed-world. The description usefully adds that no signup/auth is required and that results are deterministic, which is genuine behavioral context an agent cannot get from the annotations alone. It still omits the formula assumptions and output shape.

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?

Three short fragments with the purpose front-loaded and no wasted prose. 'Simple' is filler, and the terseness arguably costs clarity, but there is nothing to trim.

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 four-parameter financial calculator with no output schema and no parameter documentation, the description should explain input units/formats and at least sketch the return value. It provides neither the formula framing nor any output indication, leaving the agent to guess at percent-vs-decimal conventions.

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 0% across four parameters, two of them required, so the description carries the full burden and largely fails. Only 'monthly churn' loosely hints at the meaning/periodicity of monthlyChurnPct; it says nothing about units (percent vs fraction), what grossMarginPct or acquisitionCostUsd do, or which inputs are optional.

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 names a specific computation: lifetime value estimated from monthly churn, which is more than a restatement of the tool name. It does not, however, differentiate this calculator from financial siblings such as penny_margin, penny_target_price, or penny_marketplace_profit, and it never states the inputs it consumes.

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 or when-not-to-use guidance and no alternative tool is named. 'Free, no signup, deterministic' is a property statement, not usage routing, and the agent is left to infer this is a modeling calculator rather than a data-fetching tool.

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