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

Beyond annotations (readOnlyHint=false, openWorldHint=true), the description adds significant behavioral context: it is asynchronous, returns a generation_id, requires polling get_generation until status is 'completed,' and costs $0.35 per photo. This is valuable operational information not available in the structured fields, and it does not contradict any annotation.

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 three concise sentences with no wasted words. It front-loads the core purpose ('Swap several faces in one photo'), then adds cost and async behavior. Every sentence earns its place, and the structure is easy to scan.

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 the async nature and absence of an output schema, the description adequately explains the return pattern (generation_id + polling). It does not explicitly mention that only face_1 and face_2 are required while face_3/face_4 are optional, nor does it mention the consent requirement, but the schema covers those. The description is complete enough for an agent to invoke and poll the tool correctly.

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% description coverage, so each parameter is already well-documented. The description adds no parameter-level meaning beyond the schema, which keeps it at the baseline of 3. It does not explain the roles of face_1 through face_4, group_image, or consent, but the schema already covers those.

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 states a specific verb and resource: 'Swap several faces in one photo.' The qualifier 'several' clearly distinguishes it from the single-face sibling face_swap and other face-editing tools. An agent can immediately determine this is for multi-face replacement, not for single swaps, video, or GIF variants.

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 implies usage for multi-face swaps by saying 'several faces,' which hints at when to use it, but it does not explicitly name alternatives or say 'not for single face swap.' It gives an async usage pattern with get_generation, which is helpful, but lacks explicit exclusionary guidance relative to the many sibling tools.

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