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

Beyond the bare annotations, the description discloses meaningful behavior: it is project-scoped to the explicit project_id, saves a video_clip, does not place it in the program until insert_media, omits audio, and caps duration at 1-20s. This gives the agent clear expectations about side effects.

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 dense but every sentence serves a purpose: scope, core behavior, anti-pattern warning, parameter semantics, and post-processing notes. It is front-loaded with project-scoping, though the repeated 'PROJECT-SCOPED' phrasing is somewhat redundant.

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?

The description covers composition rules, duration limits, file persistence, insertion status, and audio behavior. However, with no output schema, it only vaguely says 'returns the project identity with its result'—it does not specify the exact response shape or whether the operation is synchronous or asynchronous, leaving some uncertainty for an agent invoking it.

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 schema only lists `columns` as a bare array and `duration_s` as a number, with 33% description coverage. The description compensates by explaining the two valid formats for columns (list of asset_keys or list of column clip-lists) and defining each clip's structure as {asset_key, start, duration}, plus the valid range/default for duration_s.

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 states precisely what the tool does: 'build ONE 16:9 clip that shows 2 or 3 independent videos side-by-side on a solid BLACK canvas'. It also distinguishes itself from the naive approach ('Do NOT fake this with pad_blur inserts plus small PIP overlays'), making its unique purpose clear relative to sibling tools.

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?

It gives strong context for when to use the tool—creating the signature multi-panel athlete/action wall—and explicitly warns against faking it with pad_blur inserts and PIP overlays. It also points to follow-up steps: insert_media with fit='pad' and add_music for audio. It doesn't name specific alternative tool names, but the guidance is usable.

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