Add image watermark

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

No annotations are provided, so the description carries the full burden of behavioral disclosure. It only restates the core operation without explaining side effects: whether the source video is modified or a new file is created, how the output_path default works (it is not required in the schema), or any preconditions like codec compatibility. This is a significant gap for a tool that writes output.

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 a single sentence of 16 words, front-loaded with the verb 'overlay' and the resource. It is concise, well-structured, and contains zero filler, making it easy for an agent to parse quickly.

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?

Despite a rich schema, the description omits important context: it does not clarify that this is a video-processing operation that produces a new file (output_path is optional but not explained), nor does it describe the return value or how transparency in the watermark image is handled. The relationship to sibling tools like picture_in_picture is also unaddressed, leaving the agent to infer when to select this tool.

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?

The input schema has 100% description coverage, with all six parameters documented including defaults and enum values. The description adds no additional meaning beyond mentioning 'size and opacity,' which are already covered by the width and opacity schema descriptions. Thus, the baseline of 3 is appropriate.

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 tool overlays an image (logo/watermark) onto a video, specifying corner placement and optional size/opacity. This is a specific verb+resource that distinguishes it from sibling tools like add_text_overlay or draw_box, which handle text or shapes instead of images.

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 used when the user wants to add an image watermark to a video, with clear context about corner positioning and sizing options. However, it does not explicitly mention when not to use it or provide alternatives such as add_text_overlay for text-based watermarks, so it lacks explicit exclusions.

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