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

Annotations only declare the generic profile (not read-only, not idempotent, not destructive); the description adds the materially important behavior that this incurs a 'new charge' and reuses the existing Look, background media, and loops so prior work is not re-billed. That cost and reuse disclosure is exactly the kind of context annotations cannot carry, though it says nothing about permissions or processing time.

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?

Two tight sentences with zero filler; the core action and eligible states come first, and the cost/reuse caveat follows logically. Nothing is repeated from the schema or annotations.

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 single-parameter, no-output-schema operation, the description covers the action, the eligible input states, and the billing/reuse consequences - everything an agent needs to decide and call correctly. No return-value explanation is required.

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?

With one parameter at 100% schema description coverage, the schema already documents video_id fully. The description adds no format, length, or ID-source detail beyond it, so 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 description states a specific verb ('Run ... again') and resource ('a finished, failed or cancelled video'), making it immediately distinguishable from siblings like create_video, cancel_video, and get_video. An agent can tell that this re-executes an existing video rather than producing a new one.

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?

It clearly states the applicable conditions - videos that are finished, failed, or cancelled - which tells the agent when this tool is usable rather than one of the create_* siblings. It stops short of explicitly naming an alternative tool or stating when not to use it (e.g., for in-progress videos).

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