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

Annotations already establish readOnlyHint and idempotentHint, so the safety profile is covered. The description adds genuinely useful behavioral context — that prices are median ad hoc rates incl. VAT and that per-minute/session fees are excluded — but the phantom `extra_fees` flag undercuts that clarity by promising a toggle the tool cannot accept.

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?

Four dense sentences, front-loaded with what is priced and in what currency, then input modes, then default output shape. Only the trailing extra-fees clause fails to earn its place, since it describes a capability the schema does not expose.

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?

There is no output schema, and the description compensates by naming what the no-operator call returns (cheapest, most expensive, national typical price), which is the key completeness gap for a 6-parameter calculator. It stops short of describing the per-operator return shape, and the phantom `extra_fees` reference is a real defect for an agent trying to call it correctly.

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 baseline is 3 and the schema already documents each parameter's meaning and units. The description restates the kwh vs car_battery_kwh alternative and the percent-pair combination but adds no syntax or format detail beyond the schema, and it introduces a nonexistent `extra_fees` parameter that muddies the parameter model.

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 verb and resource ('Estimate what a charge costs in EUR') with concrete scope: public chargers in Lithuania, per network, median ad hoc price incl. VAT. It is clear what the tool computes, though it never names the closest sibling (cheapest_charging) even though it also returns 'the cheapest networks', leaving an agent to infer the boundary.

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?

It does give real input guidance: supply either `kwh` or `car_battery_kwh` with `from_pct`/`to_pct`, and omitting `operator` switches to a summary view. However, there is no when-to-use versus alternatives such as cheapest_charging or operator_tariffs, and the mention of an `extra_fees: true` flag references a parameter that does not exist in the schema, which actively misleads invocation.

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