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

No annotations are provided, so the description carries the full burden of behavioral disclosure. It mentions 'リアルタイムカウントダウン' (real-time countdown) and 'Browser-based tool', but these are ambiguous: 'real-time' conflicts with the 'how many days' phrasing, and it doesn't specify whether the display updates by the second or just shows a static day count. It also omits details like whether it uses the system's current date or requires user input.

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 a single, front-loaded sentence that immediately conveys the tool's purpose with a catchy question, followed by a brief parenthetical noting it's browser-based. No words are wasted, and all information is relevant.

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?

With no output schema and no annotations, the description must explain what the user sees. It says 'how many days until Christmas/New Year/GW', which conveys the core output, but the 'real-time countdown' phrase adds ambiguity about the actual display (e.g., days only vs. hours/minutes/seconds). For a zero-parameter tool, the description is nearly complete but falls short due to this internal inconsistency.

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 zero parameters, so the baseline score is 4 per the rubric. The description doesn't need to explain parameters, and it doesn't attempt to, which is appropriate given there is nothing to configure.

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 counts down days until Christmas, New Year, and Golden Week, using a specific question format ('あと何日？') that identifies the resource and action. It distinguishes itself from general date calculators and classroom timers by focusing on these specific holiday countdowns, though it doesn't explicitly mention alternatives.

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 usage is implied: use this tool to see how many days remain until the listed holidays. However, no explicit when-to-use or when-not-to-use guidance is provided, nor are any sibling alternatives like 'date-calculator' mentioned for general date calculations.

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