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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds genuinely useful behavioral detail beyond that: the exact deterministic formula and the ceiling rounding, which tells the agent the result is an integer count rounded up rather than a fractional 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?

Two sentences: the first states the purpose, the second gives the formula. Nothing is wasted and the purpose is front-loaded ahead of the arithmetic.

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 usefully defines the return (a panel count, rounded up) and all four optional inputs have defaults in the schema. It could say more about the exact response shape (bare number vs. breakdown), but the essentials for calling it correctly are present.

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 the baseline is 3. The description goes further by showing how the parameters combine (watts/1000 × sun hours × 365 × loss adjustment) and which term each input feeds, which is meaning the schema does not convey — though the '1 − losses' form is slightly at odds with the schema's percent unit.

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 a specific verb and resource — computing the number of solar panels needed to offset annual electricity use — and names the three input drivers. It is immediately distinguishable from siblings like calc_voltage_drop or calc_appliance_energy_cost 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?

The description explains what is computed but gives no when-to-use guidance, no exclusions, and does not point to or away from any sibling calculator. The only usage hint (bills, PVWatts) is embedded in the schema parameter descriptions, not the tool description.

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