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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, but the description adds real behavior beyond that: the card is interactive and a pick arrives back as the user's message using the slug, later picks override earlier ones, the agent should 'say one line and stop', and that this call is Free. What's not covered is what happens on dismissal or whether a pick has side effects, so it stops short of fully exhaustive.

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?

Four dense, front-loaded statements — what renders, when to use it, how the interaction flows, and the fallback — with no filler. Even the terse fragments ('Free.', 'No card (terminal)') each carry 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?

For a single optional-enum, read-only UI card tool, the definition covers rendering, trigger, interaction protocol, and the alternative path; the schema handles the only parameter, so nothing an agent needs to invoke it correctly is missing.

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 coverage is 100% with a single enum parameter that already documents `shorts` as Shorts Studio versus omitting for Explainer Studio. The description repeats the same mapping rather than adding new meaning (no defaults, no format nuances), so this sits at the high-coverage baseline.

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?

The description opens with a concrete rendering statement — a card showing Explainer Studio styles (or the Shorts equivalents under `format: "shorts"`) as a grid of reels playing in place — which is a specific verb+resource, not a restatement of the name. It is explicitly distinguished from the sibling `list_studio_styles`, which is described as the terminal/no-card variant.

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?

It gives an explicit trigger (user wants a trending look and named no style), an explicit exclusion/alternative (no card/terminal → `list_studio_styles`), and additional selection rules ('a later pick wins outright', 'never list them'). An agent can route between this and the list sibling without opening either schema.

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