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 real context beyond them: the $0.02 per-calculation cost and 'no stored inputs' data-handling note are exactly the kind of operational facts annotations can't convey.

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 tight sentences: what it computes, what you supply, what it explicitly is not. Costs and data policy are last, so the essential content 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 6 params, nested objects, 0% schema coverage, and no output schema, the description leaves notable gaps: it never says what the estimate returns (array size, battery Ah, panel count) and drops two parameters. Adequate to call, but not complete for interpreting results.

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 0% (only an example object), so the description must carry semantics; it names 4 of 6 inputs conceptually but omits panel_watts and inverter_efficiency entirely. No units or meaning for 'pv_loss_fraction' vs 'peak_sun_hours' beyond the naming convention.

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 computation ('Off-grid PV energy-balance estimate') with attribution, so the agent knows exactly what it produces. It is trivially distinguishable from all siblings (endpoint/payment/listing checks), none of which do solar sizing.

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?

'Supply daily loads, peak sun hours, PV losses, and optional battery assumptions' tells the agent the required input shape, and the explicit exclusions ('No location/weather lookup, electrical design, surge or installation certification') set a clear when-not boundary. It stops short of naming an alternative tool, but no sibling overlaps this domain.

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