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

Annotations cover the mutation/safety profile (readOnly=false, destructive=false, idempotent=false), and the description adds real operational context beyond them: ~1 minute latency, a returned batchId checked via get_image_status, and mode-dependent behavior (new images use brand settings, edits preserve the original scene). It does not mention auth/permission needs, so not a full 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?

Front-loaded with the core create/edit duality and packed with routing information; every sentence earns its place. It is a dense single paragraph with heavy em-dash use, which is slightly harder to scan but not padded.

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 7-parameter async generation tool with no output schema, the description covers the workflow, the polling path (batchId -> get_image_status), prerequisites, mode behavior, and sibling alternatives. An agent has everything needed to call it correctly.

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 adds cross-parameter and cross-tool meaning the schema cannot — imageUrl switches the call into edit mode, and referenceImageUrls must come from use_character_reference to render the actual person. It does not explain count/imageType/aspectRatio defaults, which the schema already handles.

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+resource ('Create a standalone image from a description, or EDIT an uploaded image') and explicitly distinguishes the two modes by the imageUrl parameter. It also names the siblings it is not (change_image, create_post_from_image), so an agent can route correctly 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?

Gives explicit when-to-use ('when the user asks for an image, a picture, a thumbnail or a graphic rather than a post'), names the alternatives for the post case, and states a prerequisite (call use_character_reference first for a named person). Nothing is left to inference.

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