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

Annotations already declare readOnlyHint=false, destructiveHint=false, and openWorldHint=true, so the write/open-world profile is covered. The description adds real value beyond that: it discloses lossless stream-copy behavior ('without re-encoding quality loss (-c copy stream demuxing)') and the output delivery (streaming preview and full-speed download links). It stops short of auth, size limits, or failure behavior, so not a 5.

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?

Two dense, front-loaded sentences with no filler; the core action and its key constraint (lossless copy) lead. The parenthetical technical aside is useful but the MP4/MP3 phrasing is slightly narrower than the four-format enum, a minor imprecision rather than padding.

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?

With no output schema, the description compensates by describing the return artifacts (streaming preview link and full-speed download link). For a single-required-param, non-destructive write tool whose safety profile is covered by annotations, this is largely complete, though the format enumeration in the description (MP4/MP3) does not match the schema's four options.

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 all five parameters (including the nested segments pairs) are already documented in the schema, establishing a baseline of 3. The description reinforces the 'segments' input ('based on the selected highlight segments') and the copy-based output, but adds no syntax, format, or constraint detail beyond the schema.

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 gives a specific verb ('assembles and cuts'), a specific resource (media file), and a specific output (consolidated FastStart MP4/MP3 clip built from selected highlight segments). It also implicitly ties the operation to the discover_highlights workflow via 'based on the selected highlight segments', making it distinguishable from the upload/upload_chunk siblings.

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?

Usage is implied by the phrase 'based on the selected highlight segments', which signals this is a post-discovery step, but there is no explicit when-to-use/when-not guidance, no prerequisites stated, and no named alternatives among the siblings. Adequate but leaves the agent to infer placement in the workflow.

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