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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint=false, destructiveHint=false. The description adds real content beyond that: 'Free, no key,' which tells the agent there is no auth or credit cost, plus an inventory of what the payload contains. It stops short of describing response shape, but the 'free, no key' disclosure is genuinely useful non-annotation context.

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?

It is front-loaded with 'Free, no key,' which is good, but the remainder is a dense run-on: '10 variants with every config field and its default, the bars presets, frame sizes per aspect, and pricing (same as the burn).' Jargon like 'the bars presets' and 'same as the burn' requires rereading. Little fat, but poor parseability.

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 input params and no output schema, the description carries the full burden of explaining what comes back. It lists categories of content (variants, defaults, presets, frame sizes, pricing) but not the shape or format of the response, leaving the agent to guess how to consume 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?

The tool takes zero parameters and schema coverage is 100%, so there is nothing for the description to disambiguate. The audioVisual and style_preview references describe how to consume the result in other tools, not params here, and they add a small amount of useful connective tissue.

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 never states outright that this tool returns the visualizer catalog. The clearest fragment, '10 variants with every config field and its default, the bars presets, frame sizes per aspect, and pricing,' is a noun phrase with no verb, so purpose is inferred from the name. It does distinguish itself from siblings by naming caption_video, burn_captions, and style_preview, which helps.

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?

'Pass the chosen look as audioVisual' implies you call this first when running caption_video or burn_captions on audio-only input, and 'style_preview with audioVisual shows it free' implies a preview alternative. But neither the workflow nor any exclusion is spelled out explicitly. The agent has to reconstruct the call sequence.

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