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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered. The description adds genuinely new behavior: the two-phase async nature (launch status returned now, file id only after the user finishes), client gating, and the consumer tools. Not a 5 only because it doesn't mention auth or failure/timeout behavior when the user never completes the upload.

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, front-loaded with purpose, then downstream use, then preference, then fallbacks and return behavior. No filler and each sentence carries distinct information.

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 an output schema present, annotations covering safety, and zero parameters, the description supplies everything else an agent needs: platform constraint, fallback routing, the id format, the consumer tools, and the asynchronous return timing.

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 tool takes zero parameters, so the baseline is 4; there is nothing for the description to clarify beyond noting that the file id arrives asynchronously rather than as an argument.

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 ('Open an in-chat file uploader') plus the platform gate (ChatGPT only) and the payload produced (vg_file_... id for downstream video tools). An agent can distinguish it from upload_file/create_file_upload immediately.

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 names the fallbacks (upload_file for small files, create_file_upload for large files) and the condition selecting them (clients without in-chat UI), and states a preference rule ('Prefer this over asking the user to paste a link'). This is exactly the when/when-not/alternative guidance wanted.

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