overlay_video

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

With no annotations provided, the description carries full burden for behavioral disclosure. It mentions the picture-in-picture effect but lacks critical details: whether it modifies original files, what permissions are needed, how errors are handled, output format, or performance characteristics. For a video processing tool with 6 parameters, this leaves significant behavioral gaps.

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 appropriately sized and front-loaded: the first sentence states the core purpose, followed by a clear parameter section. Each parameter explanation is brief but informative. There's minimal redundancy, though the Chinese-only format might limit accessibility in some contexts.

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 6 parameters, no annotations, and no output schema, the description provides adequate parameter semantics but lacks behavioral context. It covers what the tool does and parameter meanings, but doesn't address mutation behavior, error handling, or output characteristics. For a video processing tool, this leaves important gaps despite good parameter coverage.

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 0%, so the description must compensate. It provides meaningful explanations for all 6 parameters: clarifies 'background_video' and 'overlay_video' roles, explains 'position' enum values with detailed mappings, and defines 'dx' and 'dy' as offset values. This adds substantial value beyond the bare schema, though some details like file format requirements remain unspecified.

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's purpose: '两个视频叠加，注意不是拼接长度，而是画中画效果' (overlay two videos with picture-in-picture effect, not concatenation). It specifies the verb ('叠加' - overlay) and resource (videos), and distinguishes from sibling tools like 'concat_videos' by emphasizing it's not concatenation. However, it doesn't explicitly differentiate from all siblings like 'scale_video' or 'clip_video'.

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 usage context by stating '画中画效果' (picture-in-picture effect) and contrasting with concatenation, suggesting this tool is for overlaying videos rather than joining them end-to-end. However, it doesn't provide explicit guidance on when to use this versus alternatives like 'scale_video' or 'clip_video', nor does it mention prerequisites or exclusions.

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