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

Beyond the annotations (readOnlyHint=false, openWorldHint=true, idempotentHint=false), the description discloses that a copy is written into account uploads, size and format limits, and that private/internal addresses are refused. It does not say whether re-importing the same URL creates a duplicate or how long the imported asset persists, which is why this is not a 5.

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?

Three short sentences with zero waste: the copy action and limits come first, then how to use the returned path, then the security refusal. Every sentence carries information an agent needs.

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?

A single required parameter, no output schema, and the description covers the return value ('returns its path'), the accepted inputs, and the failure case. Nothing an agent needs in order to call it correctly 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%, so the baseline is 3, and the description earns above that by adding constraints the schema lacks: HTTPS only, specific image formats, a 10 MB cap, and rejection of private/internal addresses. It does not describe any URL normalization or redirect behavior.

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 gives a specific verb and resource ('Copies a public image ... into the account's uploads') plus source restrictions (public https, PNG/JPEG/WebP, 10 MB max). It is clearly distinct from a generic upload tool, but it never names or contrasts with the sibling create_upload, so sibling routing relies on inference.

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 states the downstream use explicitly: take the returned path and pass it as params.image to generate, for image-to-video start images. That is concrete when-to-use guidance, though it offers no exclusion such as when to prefer create_upload or another upload path.

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