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

Annotations already indicate readOnlyHint=false and destructiveHint=false, so the agent knows this is a mutating but non-destructive operation. The description adds useful behavioral context beyond annotations: it states the return value ('Returns the full updated/created object') and the Space scoping behavior, which are not specified in annotations. No contradiction exists.

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 description is two sentences, front-loaded with the purpose, then the return value and Space scoping. Every sentence earns its place, with no redundant or vague wording.

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?

The tool has a complex body schema and no output schema; the description covers the key contextual elements: what the tool does, what it returns, and how Space scoping works. It appropriately leaves field-level details to the schema. Slight gaps remain, such as not mentioning that the ad group and campaign must already exist, but those are implied by the required fields and are not explicitly stated elsewhere.

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%, so the baseline is 3. The description does not add significant parameter details beyond the schema: the space_id override behavior is already fully described in the schema, and the body's structure is referenced via 'Request body matching the AdCreate schema.' The description adds little new information about 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 'Create a new ad inside an ad group' with a specific verb and resource, and clearly distinguishes it from sibling tools like create_ad_group (which creates a group) and update_ad (which modifies an existing ad). The scope 'inside an ad group' adds further precision.

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 description gives clear usage context for Space scoping: 'Scoped to the active Space — see set_active_space to switch, or pass space_id to override for this one call.' This tells the agent how to control the Space context, but it does not explicitly state when to use this tool over alternatives or when not to use it, so it falls short of a 5.

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