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

Annotations already establish readOnlyHint=true and openWorldHint=false, so safety is covered. The description adds a genuinely non-obvious trait beyond them: that missing inputs silently resolve to calculator example figures, which materially affects result interpretation and drives the explicit 'state the assumptions' instruction.

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 purpose front-loaded before the defaulting rule, with no redundancy or filler. Each sentence earns its place.

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 still conveys that three funding models are compared on three metrics, which is enough to know what comes back. It does not describe the shape of the result (per-model breakdown, units, year basis), a minor remaining gap for a computation tool.

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 per-field meanings are already documented and the baseline would be 3. The description goes beyond it by explaining the default-value semantics for every omitted parameter (example calculator figures), which the schema does not disclose.

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 ('compares') plus the exact outputs (upfront cost, yearly income, payback) and the scope (fully/part/self funded chargers). This clearly separates it from data-lookup siblings like area_charging_facts or grant_check, though it never names an alternative explicitly.

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?

Gives clear calling context: all inputs are optional and omitted values fall back to the site calculator's example figures, plus an instruction to surface those assumptions to the user. It stops short of naming when to prefer a sibling tool, so it isn't a full 5.

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