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

Adds genuinely non-obvious behavioral facts the annotations cannot convey: the returned URL is short-lived and raw bytes must be PUT to it with separate file/HTTP tools, and the call consumes no image credits. Annotations already declare readOnlyHint=false, destructiveHint=true, idempotentHint=true and openWorldHint=true, and the description does not contradict them. It omits any note on expiration duration or what happens if the subsequent PUT never occurs.

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, each earning its place: identity of the operation, the call sequence, and a cost caveat. Front-loaded and free of filler.

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?

No output schema exists, and the description still explains that a URL is returned and how to use it, plus the credit-cost caveat. Missing pieces are the meaning of 'private' (visibility/lifecycle), URL expiry timing, and whether repeated calls create separate upload slots — relevant given the idempotentHint and destructiveHint annotations.

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?

With 0% schema description coverage, the description carries the burden and does so for two of three parameters: it tells the agent that sha256 and bytes must be computed from the local file rather than guessed. mimeType is left unexplained in prose but its enum in the schema is self-documenting, so the gap is minor.

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 ('Prepare a private reference upload') and immediately follows with the concrete mechanics of the operation. An agent can tell this is the pre-upload step for reference images, distinct from generate_image or delete_reference_image, without opening the 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?

Gives an explicit ordered workflow: compute SHA-256 and byte size locally, call this tool, then PUT raw bytes to the returned short-lived URL. That is clear when-to-use guidance. It does not name alternatives or state when not to use it (e.g., versus a direct generate_image reference path), so it falls short of a 5.

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