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

Annotations already signal that this is not read-only and is open-world, but the description goes further by disclosing a concrete side effect (billing $0.03 per image) and the asynchronous execution pattern. This adds real behavioral context beyond the annotations. It does not contradict the annotations, and there is no mention of other side effects, but the disclosed information is meaningful.

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 exceptionally concise: two sentences, zero filler. The primary purpose is front-loaded, and the critical asynchronous workflow and cost are conveyed in the second sentence. Every word earns its place, and the structure is optimally scannable.

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?

Given the tool's moderate complexity (3 parameters, no output schema) and the rich sibling set, the description covers the essential operational details: purpose, cost, and the polling protocol with a specific sibling (get_generation). It omits details like possible failure modes or what the expanded image looks like, but these are not critical for a correct first call. The description is complete enough for an agent to use the tool 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?

All three parameters are fully described in the input schema with 100% coverage, including the enum for aspect_ratio and the max length for prompt. The description does not add any parameter-specific details, which is acceptable given the schema already carries the explanatory burden. The baseline of 3 applies.

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 phrase 'Extend images with AI' clearly states a specific verb (extend) and resource (images), which distinguishes it from general-purpose tools like ai_image_editor or ai_image_generator. However, it does not explicitly name an alternative tool, so it misses the full 5 that comes with explicit sibling differentiation.

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 description provides clear operational guidance: it explains that the call is asynchronous and instructs the agent to poll get_generation until status is 'completed'. This is valuable for invoking the tool correctly. However, it lacks any guidance on when to choose this tool over alternatives, leaving the selection decision to inference.

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