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

Annotations already declare readOnlyHint=false, destructiveHint=false, idempotentHint=false, and openWorldHint=true, so the description mainly needs to add context. It contributes that the reference is private, permanently stored, that audio is trimmed to 15 seconds, and that the returned handle is the durable contract — useful, but most of these details are restated from the schema, and nothing is said about failures, name collisions, or what happens on re-creation of an existing handle.

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?

Two sentences, front-loaded with the primary action and its payload formats; the return-value and usage note comes second where it belongs. It is dense with parenthetical format details but no sentence is wasted.

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?

For a 6-parameter creation tool with full schema coverage and annotations present, the description covers purpose, input formats, the audio trimming behavior, and the returned handle's role in downstream prompts. With no output schema, it correctly states the return value; remaining gaps around permissions and error behavior are minor.

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 description coverage is 100%, so the baseline is 3. The description restates the kind-to-field pairing (four image kinds take image, audio takes audio) and the accepted formats, which largely duplicates what the schema already documents rather than adding new syntax or constraints.

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 first sentence gives a specific verb (Save) and resource (a private reference) and enumerates the concrete kinds, so an agent immediately understands what is created. It does not differentiate itself from siblings such as create_upload (which apparently handles the reserved image1/image2 uploads) or create_character, leaving a small ambiguity at the boundary.

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?

The closing clause 'mention it in a generate prompt as @handle' implicitly explains why one would call this rather than anything else, tying it to the generate flow. However, there is no explicit when-not guidance, no mention of list_references/delete_reference as the lifecycle alternatives, and no statement about when to prefer create_upload.

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