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

Beyond the annotations (readOnlyHint=false, destructiveHint=false, openWorldHint=true), the description discloses the return shape (preview with plan_id), the non-mutating phase semantics, and a conditional warning surfaced when BROAD keywords land in a campaign without Smart Bidding. That is substantive behavioral context the annotations do not carry.

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 preview/non-mutation guarantee is front-loaded, followed by the plan_id mechanics and warning condition. Three tight sentences, each earning its place, with no restatement of the name or schema.

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 output schema exists and the description still flags the salient return elements (plan_id, BROAD/Smart Bidding warning), and the confirm_and_apply handoff closes the loop. An agent has everything needed to call it and act on the result.

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 schema already documents ad_group_id, keywords (with text/match_type shape), and customer_id. The description adds no parameter-level detail beyond the schema, so the baseline 3 applies.

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 names a specific verb+resource (draft keyword additions) and immediately clarifies the two-phase intent: it returns a PREVIEW and does NOT add keywords. This distinguishes it cleanly from the mutation siblings like add_negative_keywords and confirm_and_apply.

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?

It explicitly states the follow-up path — 'nothing changes until confirm_and_apply applies the returned plan_id' — which tells the agent how the draft fits into the workflow. It stops short of naming when to prefer this over alternatives such as discover_keywords or add_negative_keywords, so no explicit exclusion is given.

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