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

Annotations already declare the tool as read-only, idempotent, and non-destructive. The description adds valuable context: results are sorted by estimated cost, estimates are approximate, users should verify with official sites, and the service may receive affiliate compensation. This goes beyond the annotation-provided safety profile.

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 front-loaded with the core purpose in the first sentence, followed by necessary caveats and affiliate disclosure. While somewhat lengthy, every sentence serves a purpose (estimating accuracy, verification, legal disclosure), so structure is justified.

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?

The description covers purpose, input criteria, output ordering, and important caveats. There is no output schema, so the lack of return format detail is acceptable. It could mention edge cases like no matching plans, but overall the tool's behavior is adequately described for an agent.

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 has 100% parameter coverage with detailed descriptions, so the baseline is 3. The description adds a key semantic connection by noting that household size and monthly kWh are alternative inputs ('または'), which is not specified in the schema. This clarifies the relationship between parameters.

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?

Description uses specific verb '検索' with a clear resource ('家庭向け電気料金プランの候補') and specifies input criteria (area, amperage, household size/kWh) and output ordering (ascending estimated cost). This clearly distinguishes it from siblings like compare_plans, get_switch_link, and simulate_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 clearly implies the usage context (searching for electricity plans with cost estimates) and explains which inputs are relevant. However, it does not explicitly mention when not to use this tool or mention alternatives, so it lacks exclusions.

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