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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so safety is covered. The description adds genuine context beyond that: it names the underlying model (Sky Solar's guide calculator) and flags the output as 'an illustration, not a quote' — an important accuracy/non-binding disclaimer for a financial estimate.

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?

Three compact sentences with the deliverable front-loaded and the caveat last. Slight promotional flavor in the Sky Solar reference, but no filler or repetition.

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, closed-world calculator with full schema coverage and no output schema, the description covers what it computes, what model it uses, and how much to trust the numbers. It could be stronger by sketching the returned figures (annual vs. lifetime vs. recommended kWh), but nothing essential to calling it is missing.

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 schema already explains every parameter including defaults and ranges. The description adds only indirect color — the Verbraucherzentrale rule of thumb behind the shiftedKwh default of 1,500 — without clarifying units, interactions, or how consumptionKwh drives the sizing result.

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?

States concretely what the tool returns: annual and lifetime savings for a home battery, plus a recommended size via the Verbraucherzentrale rule of thumb. An agent can tell this is a savings/sizing estimator rather than a lookup. It does not, however, distinguish itself from the sibling size_system, which plausibly overlaps on the sizing half.

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 — 'What a home battery saves' signals the scenario, but there is no explicit when-to-use, no exclusions, and no routing to size_system, eeg_feed_in, or find_subsidies, all of which are adjacent questions an agent might confuse with this one.

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