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

The annotations already establish that this is a read-only, idempotent, closed-world calculation, so the description's main added value is the compounded-math note (5% monthly ~ 46% annually, not 60%). It does not say what happens when the optional 'period' is omitted, so the default behavior stays a mystery.

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 value proposition is front-loaded in one dense sentence with no filler. The trailing marketing URL is the only element that does not serve tool selection.

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 an output schema present, the description does not need to enumerate return values, though it helpfully names the derived outputs (monthly/annual equivalents, average lifetime) that are not obvious from the inputs. The only real gap is the unstated default for the optional period argument.

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 documented in the schema with the enum for period. The description adds nothing beyond this: it does not explain how 'customers_at_start' relates to 'customers_lost' or what the default period is, so the baseline of 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?

The description names a specific verb-and-resource pair: churn/retention over a period, plus monthly and annual equivalents and average customer lifetime. That separates it cleanly from the revenue-focused siblings (calculate_arr, calculate_arr_bridge), though no sibling is named explicitly.

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 guidance on when to use this tool versus calculate_arr or the other calculators, and no mention of prerequisites or exclusions. The trailing link to the web calculator is promotional rather than decision-oriented.

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