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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safely-reads-hosted-data profile is established. The description adds the meaningful behavioral detail that the response is interval-level plus summary statistics including negative intervals, but says nothing about unit/currency, interval spacing, or whether a missing day yields an error or empty result.

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?

A single front-loaded sentence: product, then granularity, then returned aggregates. No redundant restatement of parameters or boilerplate.

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?

For a three-parameter read-only tool with no output schema, the description covers the product concept, granularity, and what the response summarizes, while the schema carries defaults and points to grid_regions for region codes. The remaining gap is the absence of any routing cue toward grid_price/grid_price_history for non-forward pricing.

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 the baseline is 3. The description earns an extra point by tying the market value to the product actually returned (EU day-ahead versus NEM pre-dispatch) and by calling the day 'local', which clarifies that the date is interpreted in the region's local timezone rather than UTC.

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 resource and product (day-ahead EU / pre-dispatch NEM prices) plus the granularity (per interval for a local day) and the aggregate payload (min, max, average, negative intervals). It suggests a forward-looking pricing tool distinct from a live-price sibling, but never names grid_price or grid_price_history, so the split is inferred rather than stated.

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?

Usage is only implied by the words 'Day-ahead' and 'pre-dispatch' — an agent can guess this is for forward/next-day pricing rather than spot or historical. There is no explicit when-to-use, when-not-to-use, or named alternative such as grid_price_history for past prices.

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