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

Beyond the annotations, it discloses two critical behavioral traits: the campaign is created PAUSED (safe default despite destructiveHint=false), and Google rejects an asset group missing any required element. That validation behavior is exactly the kind of context an agent cannot get from the schema or annotations.

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?

Three dense sentences, front-loaded with what gets created and the paused state, then requirements, then the dependency. No filler; every clause carries actionable constraint information.

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-value explanation is unnecessary, and the description covers asset requirements and the upload dependency well. It leaves the confirm flag and the basic identity/budget parameters undocumented, which for a 12-parameter mutation tool is a noticeable gap.

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?

With 0% schema description coverage the description must carry parameter meaning, and it does for the hardest ones: minimum counts and character limits for headlines, long_headlines and descriptions, plus aspect-ratio requirements for the three image arrays and their exact parameter names. It omits meaning for customer_id, name, daily_budget, final_url, business_name and especially confirm, so it is strong but incomplete.

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 Performance Max campaign') and immediately clarifies the scope: budget + campaign + asset group + assets. It also distinguishes the output state ('PAUSED'), which separates it from the many other create_*_campaign siblings.

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 prerequisite ordering ('Upload the images first with upload_image_asset and pass the returned resource_names') and names the exact parameter slots to use. It does not say when to choose PMax over other campaign types or what happens if confirm is omitted, so it stops short of full 5.

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