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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, open-world), so the description's job is to add what they don't say. It does: it discloses the commercial behavior — free within a daily allowance, then $0.001 USDC per call via x402 — which is meaningful cost/throttling context an agent needs before calling.

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?

Two short sentences with zero filler: the measurement and its reference baseline come first, the cost model second. Every clause earns its place.

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 an output schema present, return values need no explanation, and a zero-parameter tool removes input ambiguity. The description covers purpose, comparative baseline, and pricing; the only omission is the temporal coverage/window of 'daily' values, a minor gap.

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?

The tool takes zero parameters, so there is nothing for the description to disambiguate; the schema is complete at 100% coverage. Baseline 4 applies with no compensating gap.

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 concrete verb+resource pair ('Daily GB average temperature') and adds a comparison scope ('against seasonal reference values') plus a rationale ('drives demand'). It is clear enough to distinguish from wind-forecast or demand-daily, though it never names a sibling explicitly.

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?

There is no guidance on when to pick this tool over the many nearby gb-electricity siblings (demand-daily, demand-forecast, system-prices). The parenthetical '(drives demand)' hints at relevance to demand analysis but is not a usage rule or an alternative-selection cue.

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