編集結果のマスク領域だけを土台へ貼る

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

With no annotations, the description carries the full burden and discloses notable behaviors: base is preserved bit-wise ('土台はビット単位で保たれる'), blur is applied only inside the mask ('境界のぼかしは内側にだけ入る'), and it auto-verifies base contamination if numpy is available ('numpy があれば土台の汚れを自動検証する'). It does not detail failure modes, but the disclosed behaviors go well beyond the name.

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?

Four sentences, no wasted words. The first sentence states the core function, followed by use-case, a caveat about blur, and a note about validation. Every sentence earns its place.

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?

Given no annotations and no output schema, the description covers the main aspects: purpose, use case, key behaviors, and edge-case handling (blur direction). It does not mention return values or error behavior, but for a compositing utility the provided context is sufficient for an agent to select and invoke 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?

Schema coverage is 100%, so each parameter already has a description. The description adds relationships between parameters (e.g., src_path is 'edit_image の出力', base_path is the fixed face) and explains the feather behavior (blur only inside), which enhances the meaning of the feather parameter. It scores above baseline 3 due to this cross-referencing.

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 a specific verb+resource: 'edit_image の結果からマスク領域だけを切り出し、土台画像へ合成する' (cut out only the masked area from edit_image result and composite onto base). It distinguishes from siblings by explaining the compositing role and even gives a concrete use case: 'アバターの差分絵を作るなら必ずこれを通す' (if making avatar diff images, be sure to use this).

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 explicitly tells when to use the tool ('アバターの差分絵を作るなら必ずこれを通す'), and implies that it is the step after edit_image. It does not explicitly list alternatives or when-not-to-use, but the context is clear enough that it is the compositing step among the sibling tools.

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