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

With no annotations, the description carries the full burden, and it delivers: it discloses that calculations follow '古典の暦法' (classical calendrical methods) and that '生成 AI は答えを作らない' (the AI does not fabricate answers), signaling deterministic computation rather than generation. It also specifies that exactly one result is returned and lists its components, giving an agent a clear behavioral model.

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, then a compact list of output elements, then constraints and method. Each of the four sentences earns its place, and the somewhat long list of components is justified because there is no output schema to define return values.

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 single-parameter tool with no annotations and no output schema, the description is remarkably complete: it explains what is returned, the calculation method, the non-hallucination guarantee, and the input constraints. The only missing details (e.g., response formatting) are minor and can be inferred from the listed components.

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 parameter is already documented with an example and default-year behavior. The description adds extra semantic value by reiterating that the input is a birth date and, importantly, '出生時刻は不要' (birth time is not required), which is absent from the schema. This helps an agent ignore any time component in user input.

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 identifies the tool's action: '生年月日から、その年の占いの結果を1つ返す' (returns one annual fortune result from a birth date) and enumerates the exact fortune components, making the resource unambiguous. However, with no sibling tools, it doesn't actively differentiate itself from alternatives, which keeps it from a 5.

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 gives clear invocation context: a birth date is the required input, and '出生時刻は不要' explicitly states that birth time is not needed, guiding the agent to strip/ignore time info. It implies the default annual scope ('その年'), and the schema adds the current-year default. There are no alternatives to exclude, so the guidance is as complete as the sibling set permits.

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