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

Annotations only declare readOnlyHint and closed-world, so the description carries the rest of the burden and does so richly: it discloses the fee (15%), the 6-month cap, default rates, the provenance of each rate (RevenueCat SOSA 2026 vs. explicit assumptions), and warns the cancellation rate is a reference, not a forecast. That is exactly the kind of context annotations cannot supply.

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?

It is a single dense sentence that front-loads the formula and then the defaults, with no filler. The stacked-clause structure is slightly run-on, but every clause (fee, cap, provenance, caveats) earns its place.

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 no output schema, the description should ideally say what comes back (a per-segment estimate, a total, net-of-fee), which it only implies via the formula and fee mention. Otherwise it is complete: inputs, defaults, ranges, cap, and caveats are all covered for this read-only estimator.

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 already 100%, so 3 is the floor, but the description goes further by explaining how the parameters combine (segment loss × return rate × price, capped at 6 months, minus the 15% fee) and by labeling months_paid as an upper bound and each return rate as default/assumption. This gives the agent meaning beyond the per-field strings.

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+resource (estimate win-back revenue) and even pins the exact formula and source calculator, so an agent knows precisely what computation runs. It does not explicitly differentiate itself from siblings like get_winback_pricing, but the purpose is unambiguous without opening the schema.

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 explicit when-to-use or when-not-to-use guidance, and no mention of the sibling tools. The clause 'a reference not a forecast' hints at how to interpret the output but never states the conditions under which this tool should be selected over get_apple_retention_facts or get_winback_overview.

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