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

Annotations already declare the full safety profile (readOnly, idempotent, non-destructive, closed-world), so the bar is lower. The description adds no behavior beyond that — no note on whether this is a pure deterministic formula, what units the result is in, or any assumption/limitation. It is not contradictory, just thin.

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?

Two sentences, front-loaded with the computation and free of padding. The trailing marketing URL is arguably filler rather than functional content, which keeps it from a 5.

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 4-param calculator with no output schema, the description covers what goes in and roughly what comes out, but never states the return shape or units of the ARR estimate. Adequate but with a visible gap.

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 the four parameters are fully documented in the schema; per the baseline rule a 3 applies. The description adds no extra parameter meaning (e.g. whether percentages are 0-100 or 0-1, or whether ACV is per-customer annualized).

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 result ('Estimate the expansion ARR') and a precise scenario ('cross-selling a second product into your existing single-product customer base'), which is more specific than most sibling calculators. It stops short of explicitly distinguishing itself from near-neighbors such as expansion_revenue_impact_simulator or customer_expansion_revenue_matrix, so an agent must infer the split.

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 named alternative. The scenario description implies a context, but an agent choosing among ~100 growth calculators gets no routing help.

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