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

With no annotations, the description carries the full burden and does well: it discloses that this creates no job, spends no video minutes, and does not touch the daily limit, and that redoing it is safe. It stops short of stating where the image lives or how long it persists, but the cost/side-effect profile is unusually well covered.

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 tight sentences that are front-loaded with purpose, then workflow, then cost rationale, then the hand-off instruction. The composition sentence is descriptive but earns its place by telling the agent what the user will be shown.

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?

Five parameters are fully documented in the schema, there is no output schema, and the description compensates by explaining the returned image_url and the confirm-gate role. An agent has everything needed to call it correctly and route to create_video afterward.

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 baseline is 3, but the description adds a real cross-tool constraint the schema cannot express: the same face_side value must be reused in create_video, and the returned image_url is the handle to carry forward. That is genuine added meaning beyond the field descriptions.

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?

States a specific verb and resource — 'Generate the one held image a Single Scene video is built around' — and even describes the composition (close portrait on one side, rest out of focus) so the agent knows exactly what artifact this produces. It is clearly distinct from siblings like generate_image or animate_scenes by tying itself to the Single Scene workflow.

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?

Explicitly places the tool in the workflow: show the image to the user, let them confirm or request another, then call create_video. It also names the exact follow-up condition ('pass the returned image_url plus the SAME face_side to create_video with format single'), leaving nothing to inference.

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