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

Annotations already declare readOnly=false, destructiveHint=true, idempotent=false, and openWorld=true, so the mutation profile is covered. The description adds genuinely useful behavior beyond that: it explains that an ENABLED ad in a running campaign serves immediately from the campaign budget once Google approves it, and that PAUSED holds it. It does not mention that creation cannot be undone or any required OAuth/permission scope, which keeps it short of a 5.

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 purpose is front-loaded, followed by a short explanatory paragraph, then a clean Args section and a one-line Returns. Given that the schema has no parameter descriptions, the long Args block earns its space; the Returns note is slightly redundant because an output schema exists.

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 non-idempotent, destructive-annotated mutation tool with an output schema, the description covers what is created, all constraints, the status semantics, and the return value. An agent has everything needed to invoke it correctly; the only gap is sibling routing, which is not essential here.

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 it does: customer_id format ('numbers only, no hyphens'), headline min/max counts and 30-character limit, description min/max counts and 90-character limit, path1/path2 optionality plus 15-character limits, and status enum values with default. This is complete semantic coverage for all 8 parameters.

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 states a precise verb and resource ('Creates a responsive search ad in an ad group') and follows with a one-line explanation of what an RSA is, so an agent knows exactly which entity is produced. It distinguishes the ad type from asset-creation siblings (create_text_asset, create_image_asset, etc.) by naming the ad unit explicitly, though it never contrasts itself with those tools in words.

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?

Usage is only implied: you call this when you need an RSA placed in an existing ad group. There is no explicit 'use this instead of create_text_asset' or prerequisite guidance (e.g., that the ad group must already exist, or that headlines/descriptions become assets), and no when-not-to-use conditions.

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