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

Annotations only declare readOnlyHint=false and destructiveHint=false; the description goes well beyond them by warning that earlier ideas and their pictures are replaced, quoting a cost of about 4 credits with the actual amount returned in the result, and restricting scope to long videos. These are exactly the side effects an agent needs before invoking a non-read-only tool.

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?

Five short sentences, front-loaded with what is produced, followed by side effects, cost, constraint, and next step. No filler or repetition; each sentence carries distinct information.

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 still characterizes the return value (three labelled ideas plus a credit figure). Side effects, cost, scope restriction, and the follow-up tool are all covered, leaving nothing material an agent would need before calling it.

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?

There is a single parameter at 100% schema description coverage, and the schema already explains where videoId comes from (draft_video, list_my_videos, get_video). The description adds only the implication that the video must have a script, which is modest added meaning.

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 and resource (writes three thumbnail ideas A/B/C) and enumerates the produced artifacts: on-image words, angle, matching YouTube title, and scene to draw. It is clearly distinguished from the sibling draw_thumbnails (which draws pictures) and implicitly from show_thumbnails.

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?

Gives an explicit precondition ('Long videos only') and a workflow hand-off ('Then draw_thumbnails draws the pictures the user wants'), which tells the agent the correct next step. It does not name show_thumbnails for reviewing existing ideas, so the routing guidance is strong but not exhaustive.

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