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

Annotations only declare readOnlyHint=true, so the description carries the rest and does so well: units (euro cents per kWh), VAT exclusion, bidding zone, timezone bucketing, aggregate fields, and the data-availability window for tomorrow. The note that 15min yields 96 values a day since 2025-10-01 and exposes short dips is exactly the kind of behavioral detail annotations cannot 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?

Front-loaded with what the tool returns, then usage, then the exclusion, then the timing caveat, then the parameter hint. Dense but every sentence carries distinct information; nothing is padding or restatement of the name.

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, yet the description fully describes the return shape (per-hour prices by Europe/Vilnius hour plus daily average and cheapest/dearest hour, and the 15min pair format). For a two-enum, read-only lookup tool, an agent has everything needed 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 coverage is 100% and both parameters are enums already documented, so baseline is 3. The description goes further by explaining why resolution="15min" matters (quarter-hour dips hidden by hourly averages) and by framing date as today-or-tomorrow with an implied default, adding decision value rather than just restating enum values.

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+resource (hourly wholesale electricity prices for Lithuania, Nord Pool day-ahead LT zone) with units, VAT treatment, timezone, and the aggregates returned. It explicitly distinguishes itself from retail/public charging price tools, so an agent can separate it from charging_cost and operator_tariffs without opening a 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?

Gives a concrete use case (timing home charging on a dynamic tariff) and an explicit exclusion ("Not a retail or public charging price"), plus a timing caveat that tomorrow's data appears around 14:00 Vilnius time. It stops short of naming the sibling tools by name, leaving the routing to the agent.

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