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

Annotations are minimal (readOnlyHint=false, destructiveHint=false), so the description carries the burden. It discloses that the tool generates a new image, removes source brand traces, switches the active brand when brandId is provided, and bills as one image generation. It does not detail error handling or output format, but these are minor for a generation tool. The description covers key behavioral traits beyond the annotations.

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?

The description is somewhat long but every sentence adds essential information: purpose, parameters, usage boundaries, and billing. It is front-loaded with the core purpose and then clarifies constraints and side effects. The all-caps emphasis ('IMAGES ONLY') quickly signals the primary usage restriction. While not terse, it is efficiently structured for the content it conveys.

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 two-parameter generation tool, the description covers the core usage: what it does, what to pass, how to select a brand, and the billing implication. It does not mention prerequisites like needing a saved brand or credit balance, but these are implied by 'uses your saved brand' and 'bills as one image generation.' The lack of an output schema is acceptable given the tool's simple nature. Overall, it is sufficiently complete for an agent to call 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 description coverage is 100%, so both parameters are already documented. The description adds a small amount of extra value by noting that brandId switches the active brand 'like use_brand' and by reiterating the purpose of imageUrl as 'the static ad image to remix.' This does not significantly exceed the schema's own descriptions, so a baseline 3 is appropriate.

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 clearly states the tool's purpose: it remixes a static ad image into an on-brand version, preserving layout but replacing branding. Specific verbs ('rebuild', 'remix') and resource ('static ad image') distinguish it from sibling tools like render_ad (for video) and generate_image. The scope is unambiguous.

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?

Explicitly instructs when to use: 'IMAGES ONLY — for video ads use render_ad.' Also explains how to target a specific brand via brandId and notes the side effect of switching the active brand. This provides clear routing and usage context, covering both when to use and what to pass.

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