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

Annotations already declare readOnly, idempotent and openWorld, so safety is covered. The description adds two real behavioral facts beyond that: the optimisation objective is a choice between cost and carbon, and the horizon is capped at four days. It says nothing about what a plan contains (sessions, prices, savings), which matters because there is no output schema.

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 with no filler. The compression costs a little readability ('by a ready-by time up to four days ahead'), but nothing is wasted.

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?

This is an 18-parameter planning tool with no output schema, and the description gives no sense of the result shape, no usage context, and no pointer to its nearest alternatives. The schema carries almost all the burden, leaving the description inadequate for a tool of this complexity.

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 description coverage is 100% and the schema itself routes the agent to list_regions and list_tariffs and explains timer vs smart modes. The description adds no parameter detail beyond loosely echoing optimise and day, so the baseline 3 applies.

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 resource (the cheapest or greenest half hours to charge an electric car) and a specific constraint (ready-by time, up to four days ahead), which separates it from battery and heat-pump siblings. It never names the closest alternatives (find_cheapest_window, plan_home_battery), 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?

There is no when-to-use or when-not-to-use guidance, and no mention of find_cheapest_window or plan_home_battery as alternatives. An agent must infer routing criteria from the one-line purpose alone.

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