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

Annotations declare destructiveHint=true, and the description earns that back by explaining that bid_modifier 0 excludes the device entirely – the concrete meaning of the destructive flag for this tool. It stops short of stating auth requirements, whether the campaign must be running, or whether the change is reversible.

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?

Four compact units, each covering one parameter or the core action, with the action stated first. No filler sentences and no restatement of the title.

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 values need no explanation, and for a four-parameter mutation the description covers the risky semantics and all non-obvious parameters. Nothing an agent needs in order to invoke it correctly is missing, aside from optional permission detail.

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 coverage the description carries the load, and it does: it enumerates the accepted device values (which the schema does not constrain via enum), translates the numeric multiplier into percentages, and explains the 0 edge case plus the optional workspace slug. Only campaign_id is left unexplained, which is close to self-evident.

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 specific verb and resource (set a campaign's device bid modifier) and names the affected entity precisely. It does not, however, differentiate itself from nearby siblings such as ads_update_campaign_bidding_strategy or ads_update_ad_group_bid, so an agent must infer the boundary from the tool name alone.

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 implied by the domain semantics – adjust bids per device – and the workspace note clarifies the multi-workspace case. There is no explicit statement of when to prefer this over the bidding-strategy or ad-group-bid tools, and no prerequisites or exclusions are given.

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