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

Annotations only declare the safety profile (non-readonly, non-destructive, non-idempotent, closed-world). The description adds real behavioral context the annotations cannot convey: the URL expires in one hour, each call yields exactly one image and up to 5 are allowed, an HTTP multipart POST is required with every upload.fields entry as a form field plus the file in 'file', and the call is refused without rights confirmation.

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?

Front-loaded with the audience constraint and the core action, and every sentence carries operational information. The multipart-POST sentence is long and parenthetical, which slightly hurts scanability but not correctness.

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 explains the return value (reference_image_key) and exactly where to pass it (create_video's reference_image_keys), plus the expiry window and per-image call limit. An agent has everything needed to chain this into a working upload flow.

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. The description goes beyond the schema by spelling out the user-facing protocol behind rights_confirmed (tell the user about ownership/infringement liability, get their OK) and by tying file_type to png/jpg uploads, though it does not discuss the jpeg enum alias.

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 concrete verb+resource (a one-hour presigned upload URL for one reference image, png/jpg) and immediately scopes it to clients that can make HTTP requests. Sibling tools in the same family (get_reference_upload_page, upload_reference_image) are named as the non-HTTP alternatives, so the agent can tell them apart without opening any schema.

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?

Explicit routing: use this tool when the client can make HTTP requests; 'Chat apps: use get_reference_upload_page or upload_reference_image.' It also gives the exact call pattern (one call per image, up to 5) and the mandatory precondition (rights_confirmed must be true after informing the user).

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