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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is captured structurally. The description adds the useful behavioral detail that nothing is changed during the preview, reinforcing the annotations, but it does not disclose other behaviors such as cost calculation caveats or plan-tier assumptions beyond what the annotations and output schema already communicate.

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 a single, front-loaded sentence that states the action, the object, the condition, and the safety guarantee without any filler. Every word contributes value.

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 simple preview tool with one well-documented parameter, explicit read-only annotations, and an output schema, the description fully covers the agent's needs. It explains what the tool does, what input it requires, and that it has no side effects, leaving no critical gap for correct invocation.

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%, with the single parameter desiredKeywordCount already fully described as 'Total number of active keywords you want.' The tool description repeats this concept ('desired number of active keywords') but adds no new meaning beyond the schema, so the baseline of 3 is appropriate.

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 uses a specific verb ('Preview') and resource ('plan and price required for a desired number of active keywords'), which clearly identifies the tool's function. The phrase 'without changing anything' reinforces that this is a read-only estimation tool and distinguishes it from sibling activation or keyword-management tools.

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 clearly implies the tool is for checking billing before committing to a keyword count, and the 'without changing anything' phrase signals a non-mutating preview. However, it does not explicitly name alternatives such as add_keywords or activate_pending_keywords, nor does it state when not to use it, so the guidance is mostly implied.

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