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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), so the bar is lower. The description adds genuinely useful preconditions (matching codec/resolution/frame rate), but omits critical merge behavior: whether input array order determines output order, output format, size limits, and whether base64 strings are required.

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?

A single front-loaded sentence with zero filler; the purpose comes first and the constraint follows immediately.

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 one-parameter tool with no output schema, the description covers the core operation and its main precondition. It still leaves the agent guessing about return value, input ordering semantics, and encoding expectations, which are consequential for a merge 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?

Schema description coverage is 0% for the single parameter filesBase64, so the description must compensate. The format-matching constraint is input-related and helpful, but it never explains that filesBase64 expects base64-encoded video strings, that at least two are required, or that ordering matters.

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?

States a specific verb (merge) and resource (multiple videos) plus the result (into one), which is unambiguous and distinct from video_trim, video_compress, video_convert. It stops short of explicitly contrasting with the nearest alternative (e.g., video_convert as a pre-step), so it lands at 4 rather than 5.

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 matching codec/resolution/frame-rate clause implies a usage path (normalize with video_convert first if inputs differ), but the description never states when to use this tool versus alternatives, nor what to do when inputs mismatched.

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