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

Annotations only declare read-only, idempotent, open-world and non-destructive, so the description carries real weight and does so: prices are EUR/MWh without VAT, taxes or grid fees, Poland and GB also return local currency in zoneInfo, and gb is a within-day Market Index Price in GBP/MWh rather than a day-ahead price. It also warns that 'forecast' days are elpriser.org's own statistical estimate, not an official forecast — a caveat an agent could not derive from any structured field.

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 the core capability and caveats packed into parentheticals rather than separate sentences, with the use-case line last. The one wasteful element is the full re-enumeration of all 40 zone codes, which largely duplicates the schema enum, though it does contribute the country-name-to-code mapping.

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 a single required parameter, no output schema, and annotations covering the safety profile, the description supplies the units, currency nuances, and forecast caveat an agent needs to interpret results. It omits anything about the shape of the hourly series returned (e.g. how many hours, ordering) and any data-freshness or rate-limit context.

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 the enum already constrains zone to the 40 valid keys, so the schema does the heavy lifting and the baseline is 3. The description does add modest meaning the enum lacks — human-readable expansions such as NO1-NO5, SE1-SE4, and 'Northern Italy (it-n)' — plus the gb currency caveat attached to that specific zone.

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 ('Get spot electricity prices (day-ahead, hourly)') and bounds it to 40 named European bidding zones, so the agent knows exactly what domain it covers. It does not explicitly distinguish itself from siblings like get_current_price, get_today_prices, or get_price_forecast, leaving that inference to the agent.

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?

'Use for "what is the electricity price in Germany / Spain / Norway today"' gives a concrete triggering question shape and clear context for invocation. It stops short of naming exclusions or pointing to the sibling tools that handle current/forecast/cheapest-hours variants.

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