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

Annotations already declare this read-only, idempotent, closed-world and non-destructive, so the safety profile is covered elsewhere. The description's one real contribution is the data-quality rule that an unknown cost is named rather than silently zeroed — valuable, but it never explains what the response looks like or how the four cost components are returned.

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 scope and range before the caveat about unknown costs. The second sentence is slightly oblique in phrasing but still carries genuine information, and there is no filler.

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 read-only calculator with no output schema, the description leaves the result shape completely unspecified — an agent cannot tell whether it gets a total, a breakdown by cost component, or currency assumptions. The missing-cost disclosure helps, but the return contract is a real 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 all three parameters (id, years, kwhRate) and their defaults are already documented. The description's 'over 1 to 10 years' merely restates the years bound from the schema and adds no format or default guidance.

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 computation: total cost of ownership over 1-10 years, itemized as purchase, installation, consumables and electricity. That is materially clearer than the bare name 'running_cost'. It stops short of differentiating from siblings such as compare_products, which may also surface cost information.

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?

Usage is only implied — an agent can infer it should call this when a product's long-term cost matters, but no when-to-use, when-not-to-use, or alternative is named. No prerequisites (e.g. needing an id from search_products) are stated, though the schema covers that.

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