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

Annotations already indicate readOnlyHint=false, so the description correctly implies a mutating operation. It adds valuable behavioral context beyond annotations: cost ($0.10 per photo) and async behavior with polling instructions. This transparency helps the agent understand side effects and workflow.

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, no fluff, front-loaded purpose. The async note and cost are included efficiently, making every word earn 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?

The description covers the essential workflow: input selfies, cost, async generation, and how to retrieve the result via get_generation. It doesn't mention consent requirement, but that is in the schema. For a tool with no output schema, this is complete enough.

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?

All five parameters have descriptions in the schema (100% coverage), so the description doesn't need to detail them. It references 'two selfies' aligning with person_1 and person_2, but adds no new semantic meaning. Baseline 3 is appropriate.

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 action ('Make couple photos') and the input ('from two selfies'), which distinguishes it from sibling tools like face_swap or image_generator. It is specific about the resource it operates on.

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?

Provides explicit guidance on the asynchronous workflow: returns a generation_id and instructs to call get_generation until completed. It doesn't explicitly name alternatives but makes the use case clear and points to the follow-up tool, which is sufficient for this context.

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