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

Annotations only declare the generic write profile (readOnly=false, destructive=false, idempotent=false); the description adds substantial non-obvious context on top: the default transparent WebM vs opaque MP4 output, that VideoGen writes animation code and then renders, the 2–5 minute expected duration, and that a long-running in-progress job is healthy rather than a failure. That latency/expectation guidance is exactly what an agent needs to avoid aborting a valid call.

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 sentences, front-loaded with purpose then differentiation, then output format, then latency and operational guidance. No filler; even the last sentence about telling the user and polling calmly carries behavioral weight an agent would otherwise get wrong.

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?

An output schema exists, so return values need not be explained, and the description fills the remaining gaps: differentiation from siblings, default output container, latency expectation, and optional reference media use. Nothing an agent needs to invoke this 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 description coverage is 100% and every parameter (prompt, fileIds, entityIds, aspectRatio, subToolModes, durationSeconds, transparentBackground) is documented in the schema. The description only restates the transparentBackground default and mentions optional reference media ids, adding no syntax or constraint detail beyond the schema. Baseline 3 is correct.

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 ('Generate an animated motion graphic video from a text prompt') and then carves out a precise niche: 'precise text animations (typing effects, kinetic typography, lower thirds) that stock or generated footage can't express.' That niche statement is what separates it from the many video-generation siblings (generate_video_clip, prompt_to_video_clip, script_to_video).

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 a clear selection criterion (use when the content is precise text animation / kinetic typography that footage can't express) plus operational guidance to tell the user about the 2–5 minute wait and to poll calmly. It stops short of naming a sibling tool as the fallback for cases where footage *would* work, so routing is inferable rather than explicit.

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