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

Annotations only mark this as non-read-only, non-idempotent and non-destructive; the description adds substantial behavior beyond that — the URL is short-lived, bytes go via HTTP PUT with the returned upload_headers, and asset_url is verified automatically. It still omits how long the URL lives and whether repeated calls create duplicate uploads.

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?

Purpose, downstream tools, return usage, and limits are packed into one front-loaded paragraph with no filler. It is dense but every clause carries operational information; a small readability cost for the run-on handoff sentence.

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?

There is no output schema, yet the description names the returned fields (upload_url, upload_headers, asset_url) and explains exactly how to use each, plus size/duration limits. Nothing needed to complete the upload-then-generate flow is missing.

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% and both parameters are documented, so the baseline would be 3. The description earns extra credit by giving per-type limits (images 20 MB, video 200 MB/30 s, audio 50 MB), which supplies meaning to size_bytes and constrains content_type beyond the enum list.

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?

Opens with a specific verb plus resource ('Starts an upload of your own image, video or audio') and immediately names the downstream consumers. It is clearly distinguishable from the other upload siblings (upload_from_url, upload_media_data, confirm_upload) because it produces a URL to PUT bytes to rather than accepting an existing URL or inline data.

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?

It gives a concrete usage context (own media for generate_video, generate_image, frame_chain, compose_scene) and the full handoff sequence to a generation tool. What is missing is explicit routing versus upload_from_url and upload_media_data, which an agent must otherwise infer from names alone.

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