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

Annotations already declare destructiveHint=true and idempotentHint=true, so the safety profile is covered. The description adds genuinely useful scope beyond that: it clarifies that timing, other captions, and the spoken audio are preserved, which narrows what "destructive" means here. It stops short of addressing partial-failure or auth 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 tight sentences, front-loaded with the action and followed by the preservation guarantee. No filler, and the second clause carries real information rather than restating the name.

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?

An output schema exists, so return values need not be described. The description covers the action and its side effects adequately, but omits guidance on the required idempotencyKey and the batch constraint (max 200 updates), which an agent must know to invoke correctly.

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 25% (only projectId has a trivial "UUID string" note). The description partially compensates by explaining that updates target words via "stable IDs" (wordId), but leaves idempotencyKey, workspaceId, array size limits, and the text-length constraint entirely unexplained in both schema and description.

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 ("Replace selected caption words") and the mechanism ("by their stable IDs"), which is easy to distinguish from the list-oriented sibling captions_words_list. It does not explicitly name or contrast any sibling, so it falls just short of the top mark.

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 description implies the use case (correcting already-existing caption words identified by ID, which presupposes a prior captions_words_list call) but never states when to use this versus alternatives or any prerequisites. Usage is inferable but not documented.

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