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

The description adds real behavior beyond the annotations: creation mutates no ad and takes effect only after an asset-group link. That is the key mental model for a non-destructive-but-mutating tool. It does not address duplicate handling, despite idempotentHint=false, which is the remaining gap.

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?

The critical behavioral caveat is front-loaded in the second sentence, and the Args block is tight. The trailing 'Tools revision' line is noise, and the Returns block restates what the output schema already provides.

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 simple three-parameter create tool, an agent has what it needs: identifier formats, the optional-name default, and the fact that linking is required for effect. The return-value explanation is redundant given the output schema exists, but nothing essential 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 0%, so the description carries the full burden and largely does: customer_id is numbers-only with no hyphens, youtube_video_id is shown extracted from a URL with an example, and asset_name documents its default-to-video-ID fallback. Only minor validation detail (length/charset limits) is absent.

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 and resource ('Creates a YouTube video asset') plus the scoping context ('for use in Performance Max campaigns'). This clearly separates it from the many sibling asset creators such as create_image_asset, create_text_asset, and create_sitelink_asset without needing the schema.

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?

Explicitly says the created asset is inert until added to an asset group, and names the sibling tools that do that (create_asset_group, add_assets_to_asset_group). That is concrete next-step routing, though it stops short of stating when to prefer this asset type over other asset creators.

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