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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint, so safety is covered. The description adds genuinely new behavioral context beyond them: the Keyword Planner throughput ceiling of roughly one request per second per account and the consequence that separate calls serialize. That rate-limit disclosure is the kind of thing annotations cannot express.

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 sentences, all load-bearing: what you get, when to reach for it, and how to batch around the rate limit. The rate-limit rationale is front-loaded into the batching instruction rather than tacked on as trivia.

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 read-only research tool with no output schema, the description covers purpose, entry condition, batching, and the rate-limit constraint, and hints that the result reports how many ideas were found. What remains unsaid (exact response shape, geo/network interaction) is minor given the schema already documents every parameter.

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 goes beyond the schema by telling the agent how to group seeds ('Put related seed keywords into ONE call (up to 20 seeds)'), which is usage semantics rather than a restatement of maxItems, and by framing seeds as a batching unit.

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 ('Research keywords for a client') and enumerates the payload the agent will get back: search volume, competition, top-of-page bid range. This clearly distinguishes it from write-side siblings like ads_add_keywords or ads_add_negative_keywords, which the agent could otherwise confuse with keyword research.

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?

'Start here when building a campaign' gives an explicit entry-point condition, and 'never invent keywords or guess volumes' is a concrete when-to-use mandate. It also tells the agent how to batch seeds across calls. It stops short of naming a specific alternative sibling, which keeps it from a 5.

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