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

Annotations already declare write (readOnlyHint=false), non-destructive, and idempotent, and the description adds genuine context by explaining what happens when no trailer exists (an animated title card is built from the cover). It does not disclose whether an uploaded trailer replaces an existing one, any size/duration/encoding limits, or permission requirements — notable gaps for an upload tool.

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?

Two short sentences, front-loaded with the action and followed by the fallback behavior, with no filler. Slightly under-informative rather than bloated.

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 three-required-parameter upload tool with no output schema, the description covers purpose and default behavior but omits replacement semantics, constraints on the video itself, and what is returned after upload. With annotations covering the safety profile, this is adequate but not complete.

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 only 33%: video_base64 is documented in the schema, while game and key are undocumented anywhere. The description partially compensates by explaining what the MP4 is for (the shared-link playback video), but adds nothing about how game and key select the target experience.

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 pairs a specific verb (upload) with a specific resource (the MP4 that plays when the experience's link is shared), which tells an agent exactly what asset this tool controls. It is distinguishable from set_cover because it names the cover only as the fallback, though it never uses the word 'trailer' that the tool name implies, leaving the mapping slightly implicit.

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?

The fallback sentence implies when to use it (when you want a real video rather than the auto-generated title card), but no explicit when-to-use, when-not-to-use, or alternative is named. There is no guidance on prerequisites such as whether the experience must exist first or how game/key identify the target.

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