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

Annotations already declare destructiveHint=false and the mutation nature, but the description adds real value by clarifying the direction of effect: it 'only ever reduces reach and spend,' which lets an agent reason about blast radius. It omits reversibility/permissions detail, but the safety signal is genuinely additive beyond the annotations.

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?

Two sentences, front-loaded with the core action and effect, with no filler. Every clause carries information.

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 write tool whose annotations and schema already carry the safety profile and the tricky parameters (customerId, extraFields, validateOnly), the description covers purpose, effect direction, and use context. Given no output schema, it need not document returns; only matchType semantics are left unaddressed.

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?

The description says nothing about any of the five parameters, while schema description coverage sits at only 60%: keywords, its matchType enum, and campaignId carry no descriptions anywhere. The description does not compensate for that gap, so it adds no parameter meaning.

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 ('Add campaign-level negative keywords') and immediately explains the effect ('stop ads showing for those searches'). The 'campaign-level' qualifier explicitly distinguishes it from the sibling add_ad_group_negative_keywords.

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?

Gives clear context for use ('the usual first response to wasteful search terms found via get_search_terms'), naming both the triggering situation and the sibling tool that surfaces it. It does not state when NOT to use it (e.g. ad-group-level negatives), so it falls just 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.