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

Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, so the safety profile is covered. The description adds genuinely useful context beyond that: the result is an assumption-driven estimate, "not a quote or a promise of cash savings," and the no-FX/no-tax boundary prevents misreading the numbers.

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 tight sentences: the first lists outputs, the second lists caveats. No filler, and the most important framing (what it computes) is front-loaded.

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 carries the burden of describing return values and does so by enumerating the four computed quantities. It stops short of stating units/precision or the payback formula, but for a self-contained calculator the definition is essentially 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%, so all seven parameters are already documented with units, bounds, and meaning. The description adds only the currency-consistency rule, which is already implied by the per-parameter "same currency" notes; baseline 3 is appropriate.

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 ("Calculate") and enumerates the concrete outputs: upfront and first-year cash outlay, time-valued costs, monthly net capacity value, and simple economic payback. There are no sibling tools to confuse it with, and the scope is unambiguous.

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?

It gives clear operating context — caller-supplied assumptions, single currency, and explicit exclusions (no exchange rates, no tax calculation). What's missing is any statement of when this tool should or shouldn't be reached for versus a manual estimate, but the constraints do bound usage sensibly.

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