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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description does add real behavioral context — it discloses the price source (day-ahead or pre-dispatch) and a market-dependent mode switch where GB returns the greenest window from the carbon forecast — but it never explains how the source/mode is chosen or how ties or missing forecast data are handled.

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 dense sentence with the core computation front-loaded and the market-specific exception placed in a parenthetical where it belongs. No filler, nothing repeated from the title.

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, so the description should say what comes back — the window's start time, the price/carbon value, or a ranked list — and it does not. For a four-parameter read tool with a mode switch, that leaves a meaningful gap for an agent that must interpret the result.

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 would be 3, but the description adds genuine meaning beyond the schema by explaining that the 'market' parameter changes semantics on GB (greenest from carbon forecast rather than cheapest from prices). 'N hours' and 'horizon' merely restate the hours/horizon fields.

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 names a specific computed resource — 'cheapest contiguous window of N hours' — over a defined horizon, which is clearly distinct from the raw series tools (grid_price, grid_day_ahead). It does not name any sibling to contrast with, so differentiation is implied 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: 'in the next horizon from day-ahead or pre-dispatch prices' hints at a planning use case, but there is no explicit when-to-use versus grid_price/grid_day_ahead guidance, nor any stated exclusions or prerequisites.

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