アカウント情報と今日

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

With no annotations, the description carries the full burden and does disclose a genuinely non-obvious behavioral trait: defaultDueNext is a derived value tied to the account time zone and only matters as the fallback when due is omitted. It still does not state whether authentication (sibling sign_in) is required or what happens on failure.

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?

Two sentences with no filler: the first front-loads exactly what is returned, the second front-loads the call precondition at the end where it is most actionable. Every clause carries information.

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 must explain return values and it does so field by field, including the derived ISO8601 value. For a zero-parameter read tool the definition gives the agent everything needed to call and interpret it.

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 tool takes zero parameters, so the baseline is 4 and there is no parameter syntax for the description to add. Nothing in the schema needs compensating for.

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 the exact resource (Account レコード) and enumerates the fields returned (trialStartedAt, subscribedUntil, timeZone, defaultTime, defaultDueNext), so an agent knows precisely what it gets. It does not explicitly contrast itself with siblings like list_todos or sign_in, but the resource is distinctive enough that confusion is unlikely.

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 closing line "日付を扱う前に呼ぶ" gives an explicit precondition for calling the tool, which is real usage guidance rather than implication. It stops short of naming a when-not case or an alternative tool, so it is not a full 5.

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