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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and a closed world, so the safety profile is covered. The description adds one genuinely useful modeling assumption — growth is expansion-only, no new logos — but says nothing about return format, units, or how the three horizons are presented.

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?

Front-loaded and efficient: the computation and its scope come first. The trailing link to a full web version is promotional rather than operational and does not help an agent invoke the tool, which keeps it out of 5 territory.

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 two-parameter, read-only calculator with full annotation coverage and no output schema, the description conveys inputs and the shape of the result (1/2/3-year compounded projections). Only the exact return structure and unit conventions are unstated.

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 both parameters (arr, monthlyExpansionPct) are already documented. The description's gloss on net expansion (upsell + cross-sell minus contraction) is a modest addition consistent with the schema text, which is the baseline-3 case.

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 — compounding net expansion revenue forward 1, 2 and 3 years from current ARR — and even defines the metric (upsell + cross-sell minus contraction). It does not distinguish itself from nearby siblings like expansion_revenue_impact_simulator or net_revenue_retention_forecaster, so it falls 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?

No when-to-use guidance, no prerequisites, and no alternatives named. The horizon and the 'no new logos' constraint imply a pure expansion-projection scenario, but the agent must infer that this is the reason to pick it over other revenue models.

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