Insert a new scene into a video

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

Beyond the annotations (non-read-only, open-world, non-idempotent), the description discloses cost ('paid render, billed per second of NEW scene'), the return value ('returns the whole video's URL'), clip-length limits, and the crucial resumeTime behavior where a later time discards intervening footage. This is exactly the behavioral context annotations cannot convey.

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 core mechanism is front-loaded in the first sentence and every subsequent sentence adds distinct value: use cases, resumeTime semantics, reference limits, duration limits, and cost/return. No filler.

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 paid mutation tool with no output schema, the description covers cost model, return value, time-range constraints, and the startTime/resumeTime interaction. An agent has everything needed to invoke 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?

With 100% schema coverage the baseline is 3, but the description genuinely adds meaning: it explains that resumeTime = startTime preserves every original second while a later resumeTime cuts footage in between, and clarifies refImages/refVideos limits. It does not elaborate on the 'video' source parameter beyond 'a clip you already have'.

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 uses a specific verb and resource ('INSERT a newly generated scene into a clip') and explains the exact mechanism (plays to startTime, new scene, resumes at resumeTime). It is highly clear but never names or distinguishes itself against closely related siblings such as make_insert, edit_video, or stitch_video, which is the only thing keeping it from a 5.

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 gives concrete use cases ('product close-up, a reaction, a reveal or a missing beat in the middle of an ad without re-rendering the rest') and explains the resumeTime tradeoff, which tells the agent when this tool fits. It does not explicitly state when not to use it or which sibling to choose instead.

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