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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is established. The description adds valuable behavioral context beyond those annotations by specifying the exact outputs (daily, weekly, monthly, yearly cost plus kWh used) and noting costs are in GBP.

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 compact and front-loaded: the first sentence states purpose and inputs, the second states outputs, and the third gives currency and source. No wasted words, and the structure supports quick agent parsing.

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 simple calculator tool with a complete input schema, an output schema, and safety annotations, the description provides everything an agent needs: purpose, required inputs, return values, and units. There are no meaningful gaps.

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 schema already documents all three parameters with units and ranges. The description restates the inputs in prose but adds no extra semantic detail beyond what the schema provides, matching the baseline expectation.

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 opens with a specific verb-resource pair: 'Work out the running cost of an electrical appliance', and clearly lists the three inputs. This distinguishes the tool from siblings like fuel_cost_calculator and unit_price_calculator, which address different domains.

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 makes the intended use case clear: an agent can infer it should be used when someone wants appliance running cost from watts, hours, and pence per kWh. However, it does not explicitly state when not to use it or name alternative tools, so the guidance is implied rather than explicit.

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