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

With only a title in annotations, the description carries the behavioral burden and delivers the important non-obvious facts: images are copied into the in-app element library, durable URLs are returned, and re-using the same name replaces the existing sheet (an overwrite/upsert semantic that is not readable from the schema). It omits permission/auth requirements and any rate or size constraints beyond what the schema encodes.

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 core action, then triggers, then flow guidance, then the sibling disambiguation. It is dense rather than bloated, though the run of example trigger phrases is longer than strictly necessary.

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, but the description discloses the return value (durable URLs) and the overwrite behavior. For a 4-param upsert-style tool with full schema coverage and a title-only annotation set, nothing an agent needs to invoke 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, but the description adds real meaning for the name parameter by explaining the sheet is fetched later by that name and that re-using the name replaces the sheet — behavior the schema does not state. The kind/notes/images params are left to the (already thorough) schema.

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 (save) and resource (character sheet = named set of reference images for reuse across sessions), and explicitly contrasts with the sibling var2_upload_asset for one-off uploads. An agent can distinguish it from upload/asset tools 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?

Provides concrete trigger phrases, names the alternative (var2_upload_asset) with the condition that selects it, and sketches the intended UGC pipeline (hero image → upscale → image-to-image angles → save). When-to-use and when-not-to-use are both covered.

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