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

The description discloses several behavioral traits beyond the annotations: the $1.50 cost, the +6s duration, asynchronous execution, and the required polling workflow with get_generation. This is substantial, actionable information that the annotations do not provide.

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?

Three short sentences deliver purpose, cost, duration, and async workflow with zero filler. The most important usage fact (returns generation_id, poll get_generation) is front-loaded after the purpose.

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 simple two-param async tool with full schema coverage and no output schema, the description explains the return value and completion condition sufficiently. It could be slightly more complete by noting possible non-completed terminal statuses like 'failed', but nothing essential to invoking the tool 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 description coverage is 100%, so both video and prompt are already documented in the input schema. The description adds cost and duration context, but no additional parameter-level meaning beyond what the schema provides, matching the baseline of 3.

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 states a specific action and resource: "Make clips longer," plus the concrete output of each extension (+6s). This clearly differentiates it from siblings like ai_video_upscaler (resolution) and ai_image_expander (images), even without naming them.

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 gives clear post-invocation guidance: "returns a generation_id; call get_generation until status is 'completed'." However, it does not state when to choose this tool over alternatives or any exclusions, so the when-to-use context is only implied by the purpose.

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