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 burden of disclosing behavioral traits. It states the overlay operation and optional parameters, but fails to mention whether the output is written to output_path, whether the original video is overwritten, or any format/codec requirements. The description does not disclose the non-destructive nature (if any) or permissions needed, leaving significant ambiguity.

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, front-loaded sentence that conveys the action, target, and main options without waste. Every word adds value and no redundant details are present.

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 video-processing tool with no output schema and no annotations, the description should clarify output destination and possible side effects. It covers the core functionality but omits whether the result is written to output_path and does not differentiate from similar tools like burn_subtitles. The presence of complete schema descriptions compensates partially, but the missing output semantics leave a gap.

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 parameters are individually documented in the schema. The description adds high-level meaning (corner, size, opacity) but does not give format details or default values beyond what the schema provides. This matches the baseline of 3 for full schema coverage.

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 'Overlay' with a clear resource ('an image on the video') and includes key modifiers ('chosen corner', 'size and opacity'). This clearly distinguishes it from siblings like add_text_overlay (text overlay) and burn_subtitles (subtitle overlay).

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 makes the tool's purpose obvious: adding a logo/watermark to a video. It does not explicitly state when not to use it or name alternatives, but the context is clear enough for an agent to select it for watermarking needs. No exclusions or alternative tools are mentioned.

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