Add fade in/out

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

Since no annotations are provided, the description carries the full burden of behavioral disclosure. It discloses that both video and audio are affected and that fades go to/from black, which is useful. However, it does not clarify what happens if no fade durations are supplied (e.g., does it error or do nothing?) or whether output_path is required to avoid overwriting the input file. These gaps prevent a higher score.

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, well-structured sentence that conveys the core functionality without any redundant or tangential information. It is front-loaded and every word earns its place.

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 tool's relative simplicity (4 parameters, no nested objects, no output schema), the description covers the primary use case but leaves some edge cases unaddressed, such as default behavior when both fade_in and fade_out are omitted and the exact role of output_path (whether it is required or defaults to overwriting). This is a moderate gap in completeness, so a score of 3 is appropriate.

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 already provides 100% description coverage for all four parameters, so the baseline is 3. The description does not add additional parameter-level semantics beyond what the schema already states; it merely rephrases the fade_in/fade_out durations implicitly via 'start and/or end.'

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 the specific verb 'Fade' and clearly identifies the resource ('the video (and its audio)') and the exact behavior ('in from black at the start and/or out to black at the end'). This makes the tool's purpose unmistakable and distinguishes it from sibling video editing tools like trim_video or convert_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 provides clear context that this tool is for adding fade effects, which implicitly tells an agent when to use it. However, it does not explicitly mention alternatives or exclusions, such as 'use trim_video for cutting segments instead.' The absence of explicit alternatives is not misleading, so this is a 4 rather than a 5.

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