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

Annotations already mark the tool as read-only, idempotent, and non-destructive. The description adds valuable caveats: estimates are approximate, fuel cost adjustment rates vary monthly, government support is excluded, and users should confirm final rates on official sites. It also discloses that set discounts are conditional and shown as a separate total, adding transparency beyond the annotations.

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 concise and front-loaded, with the main purpose in the first sentence, followed by key comparison details and a clearly marked disclaimer paragraph. Every sentence adds necessary information, and the structure is logical.

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 simulation tool with no output schema and two parameters, the description covers the tool's behavior, comparison outputs, and limitations thoroughly. It indicates what the output contains (comparison totals and discounted set-total) and provides sufficient context for an agent to invoke it correctly.

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 input schema already provides descriptions for both parameters with 100% coverage. The description adds operational context by explaining that the gas supply area is automatically mapped to a corresponding power area and that household size is used for usage estimation, which helps the agent understand how parameters affect results.

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 clearly states the tool estimates combined annual electricity and gas costs when reviewing both together ('電気とガスをまとめて見直した場合の合算年間コストを試算します'). It specifies the comparison logic between cheapest plans and major regulated rates, and explains how set discounts are handled separately, distinguishing it from sibling simulation tools like simulate_cost and simulate_hikari_cost.

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 implies the use case: when a user wants a combined electricity+gas estimate. It explains the tool's scope and what it does not include (set discounts are not in the cheapest total, shown separately). However, it does not explicitly name alternatives or exclusions for electricity-only/gas-only simulations, so it falls short of full explicit guidance.

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