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

Adds substantial context beyond annotations: audio/cuts remain unchanged, a preview is returned without video encoding, empty `to` deletes words, replacement text is exact, and word-count/punctuation/capitalization changes are supported. These are precisely the behavioral traits an agent needs and they are not derivable from the readOnly/idempotent/destructive hints.

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?

Front-loads the critical scoping constraint ('PROJECT-SCOPED') before behavior, and every clause carries information. It is dense and semicolon-packed, which slightly hurts scannability but avoids filler.

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 no-output-schema mutation tool it covers scope, operation semantics, replacement syntax, and what is returned (project identity, previews, active fixes). Return shape is described only loosely, and the `clear` boolean remains unaddressed.

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?

With only 25% schema description coverage, the description compensates well: it explains the replacements anyOf form ([from,to] pairs or objects with from,to and optional start/end in OUTPUT seconds to target one occurrence) and the meaning of each operation value. It does not clarify the relationship between the boolean `clear` param and operation=clear.

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+resource: editing displayed captions via text fixes, with scoping ('acts only on the explicit project_id'). It clearly separates itself from caption-styling siblings (set_caption_style, set_caption_mutes) by describing text-level edits, though it never names a sibling explicitly.

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 operation breakdown (default replace overwrites the COMPLETE active set, append upserts, clear removes all, list returns preview) effectively tells an agent which mode to pick for a given intent. It stops short of explicit when-not-to-use guidance or naming alternative tools.

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