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

Annotations already cover safety (readOnly, idempotent, non-destructive, closed-world), and the description adds the real behavioral payload: a player appears in the chat, it targets the latest edit now and the export once that finishes, and the person saves the file via a Download button. It doesn't cover edge cases such as what is shown when a project has no edits yet, which keeps it off 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?

The core action is front-loaded in the first clause. The third sentence restates the same point ('this player is how the person sees what they changed') at some length, so it is efficient but not maximally tight.

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 reasonably explains what calling it produces: a player in the chat and a Download path for exports. A brief note on behavior when no edit or export exists is the only missing piece for a single-parameter tool.

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 with 100% schema description coverage ('Project id or exact name'), so the schema already carries the semantics. The description adds no format, lookup, or error behavior beyond it, which is the baseline 3 case.

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: it opens Cardboard's player in the chat, on the project's latest edit or on its export once finished. It also implicitly differentiates itself from siblings by naming apply_timeline, undo_timeline and caption_from_transcript as tools that produce nothing visible without it.

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 when: one call once a reply's edits are done. And an explicit why-not-alternatives: apply_timeline, undo_timeline and caption_from_transcript show nothing in the chat by themselves. An agent knows exactly when to reach for this versus the mutation tools.

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