Add video watermark

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

Annotations (destructiveHint=true) are complemented by the description stating that output_path may be overwritten and that input files are read-only. This adds behavioral context beyond the annotations, though it does not cover error handling or permissions.

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 two sentences with no extraneous information. It front-loads the core action and then lists supported features, making it easy to scan for an AI agent.

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 complexity (8 parameters, output schema), the description covers the essential behavior: read-only inputs, overwritable output, and supported controls. It does not explain return values (output schema exists), error conditions, or prerequisites, but it is sufficient for typical use.

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 coverage is 100%, so the baseline is 3. The description enumerates control types ('named, pixel, and percentage positions plus opacity, margin, CRF, and preset controls') but does not add meaning beyond what the schema already provides. It serves as a concise summary.

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 action ('overlay an image watermark onto an existing video') and the resource ('render a new output file'). It distinguishes the tool from siblings like video_overlay by explicitly mentioning 'watermark' and specifying supported position types and controls.

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 implies the tool is for watermarking but does not provide explicit guidance on when to use it versus alternatives such as video_overlay or video_add_text. No 'when not to use' or alternative tool names are mentioned.

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