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

The description adds real behavioral context beyond the annotations: it discloses that existing caption content is replaced and that output lands on a dedicated "Captions" track, and it explains that the karaoke preset highlights the spoken word. Minor tension with destructiveHint=false given the stated replacement, though the overwrite is scoped to one generated track; it still omits auth needs and what is returned.

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 sentences, front-loaded with the core action and the replacement caveat before the preset list. The preset enumeration repeats the enum but is short enough to justify as quick orientation; nothing else is wasted.

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?

Incorrectly scored here for emphasis: for an 11-parameter, nested-schema, mutation tool with no output schema and an implicit transcript dependency, this description is too thin – it should at least flag that chunking parameters control caption segmentation and that a transcript is required. This is a significant gap for the tool's complexity.

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 only 27% across 11 parameters, including a 20+ property nested text style object, and the description compensates for almost none of it – range, maxChars, maxWords, maxDuration, trackName, projectId and y are untouched. The preset list it enumerates merely restates the schema enum, adding no meaning beyond it.

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 action and target: auto-generates captions from the transcript onto a "Captions" text track. This implicitly separates it from manual text tools like add_text, but it never mentions the closest alternative, voice_captions, so an agent cannot fully disambiguate from the sibling list alone.

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 "from the transcript" – you need an existing transcript and want timed captions. There is no explicit when-to-use/when-not, no statement of prerequisites (e.g. that transcribe_media must run first), and no routing versus add_text or voice_captions.

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