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

Annotations already declare readOnlyHint and idempotentHint, and the description adds substantial behavioral detail beyond them: the oldest-first ordering with limit truncating from the OLDEST end (a genuine gotcha), per-call window limits, metric-specific availability caveats (generation limited to GB and US-CAISO, carbon-intensity to GB, capacity to European zones), and free sample-mode truncation at 50 rows.

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?

The description is long but every sentence earns its place. The core purpose and the critical truncation gotcha are front-loaded, followed by defaults, limits, metric semantics, and auth — each piece is operational for making a correct call. There is no filler or repetition of the schema's plain parameter text.

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 carries the burden of explaining return behavior, and it covers ordering, truncation, units, per-zone availability, pagination, and authentication modes thoroughly. The only gap is that it never specifies the exact output row shape/field names (beyond mentioning the 'fuel' field), so an agent cannot fully predict the response structure before calling.

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%, which sets a baseline of 3, but the description adds meaning the schema lacks: the 'limit' parameter's non-obvious oldest-end truncation behavior, default window semantics per metric type, and per-zone metric availability that the enum alone does not convey. The metric field is enriched with units (local currency per MWh, MW, gCO2/kWh) and the 'fuel' sub-field behavior.

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 first sentence states a specific verb and resource: 'Time series for one metric in one zone over a start/end window (Unix seconds).' It goes well beyond the name/title, and explicitly differentiates itself from siblings by pointing to get_latest / get_zone_brief for current values, so an agent can distinguish it from the alternatives.

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?

The description gives explicit when-to-use guidance: 'for the latest N points set start close to now, or use get_latest / get_zone_brief for current values.' It also documents pagination strategy ('paginate with start/end for more'), default and maximum windows per metric, and which metrics apply to which zones, leaving little to inference.

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