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. The description adds essentially nothing beyond the annotations – no determinism notes, edge cases, or input-domain caveats (e.g. valid percentage range) – for a tool whose only behavior is a pure projection.

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 purpose is front-loaded in a single efficient sentence. The trailing 'See the full version at...' link is mild promotional filler rather than functional guidance, a minor blemish.

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 simple two-parameter, fully-documented calculation tool with safety annotations and no output schema, the description covers what it computes adequately. It stops short of any usage context or behavioral caveats, leaving the definition minimally viable rather than 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%, and both parameters (cohortSize, monthlyChurnPct) are self-documented in the schema, so baseline 3 applies. The description adds no extra semantics such as units or valid ranges beyond what the schema already states.

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 ('project') and resource ('customer cohort decays over time under a monthly churn rate') plus the implied output ('average customer lifespan'). The scope is clearly a churn-cohort decay projection, distinguishing it from adjacent SaaS-metric siblings like net_revenue_retention_forecaster or mrr_bridge_planner, though it names no siblings 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 when-to-use guidance, no prerequisites, and no routing to alternatives despite a crowded family of SaaS metric calculators. The agent must infer applicability from the purpose sentence alone.

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