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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is covered. The description adds the arithmetic grouping of inputs, which is useful context, but says nothing about output format, units, or edge cases (e.g. zero denominator). With annotations carrying the safety burden, a 3 is appropriate.

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 first sentence is well front-loaded and precise. The second sentence is a promotional link to an external site that adds no invocation value for the agent, which costs this dimension.

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, fully required pure calculator with complete schema coverage and no output schema, the description gives enough to invoke correctly. Only minor gaps remain, such as currency units and confirmation of what the result represents.

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 coverage is 100%, so all four parameters are self-documented, and the 3 baseline applies. The description does add the numerator/denominator grouping that the individual schema fields do not convey, but that relationship is largely inferable from the parameter names.

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 states a specific verb and resource with the exact formula: divide MRR gained (new + expansion) by MRR lost (contraction + churn). This clearly distinguishes it from a generic calculator. It falls short of 5 because it never differentiates itself from adjacent siblings like mrr_bridge_planner or net_revenue_retention_forecaster.

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, when-not-to-use, or alternative guidance. The description explains what the formula is but never says when an agent should pick this over the many other SaaS/metric calculators in the sibling list.

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