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

Goes well beyond the annotations: discloses exact per-kind pricing ($0.05, $1.50, $0.10/sec), that spending hits the member's wallet and is only charged when a saved result is produced, that both video kinds are async (start here, ready in a few minutes, nothing charged yet, poll my_studio), and that the result supplies the id and final length/price. The annotations only cover safety profile (readOnlyHint=false, destructiveHint=false), so this added context is genuinely valuable.

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?

Front-loads the key facts (wallet spend, confirm price first) before drilling into the three kinds. It is a single dense paragraph, but nearly every sentence carries actionable detail; only minor tightening would be possible.

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 must carry return-value context, and it does state that results yield an id and final length/price. For a complex three-mode tool it covers modes, cost, prerequisites, and async behavior well, leaving only minor gaps in exact response structure.

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 already 100%, so the baseline is 3, but the description adds real meaning: it explains what each kind's parameters should contain (subject/angle/lighting/background for 'description', 'what moves and how the camera moves' for movement, script 'written as they would say it out loud' up to 900 characters, image_id must be an id not a link). This enriches the terse schema descriptions.

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 ('Make something in the signed-in member's Studio') and enumerates three distinct modes with what each produces: an image from a description, a 5-second video from their own Studio image, and a video of their avatar speaking a script. It implicitly distinguishes itself from siblings like my_studio (view-only) and checkout_link (payment) by routing to them for readiness and funding.

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 explicit per-kind guidance: cost, when the charge applies ('charged only when the result is made and saved'), the requirement to confirm price first, and 'one thing per request'/'one at a time'. It also states prerequisites (avatar and voice must be READY per my_studio) and offers the fallback checkout_link when the wallet is short. No explicit when-NOT-to-use statement, so it falls just short of a 5.

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