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

Annotations already declare readOnlyHint=true, which covers the safety profile of this pure calculation tool. The description adds no additional behavioral context beyond what annotations provide, such as side effects or prerequisites, but it does not contradict the annotations either.

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, clear sentence that gets straight to the point. It contains zero filler and is appropriately sized for a simple calculator tool, making it highly efficient and front-loaded.

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?

Given the simplicity of the tool, the description is largely complete. However, it does not explicitly state the formula or the return value format, though these are strongly implied by the tool's purpose and the parameter names. Annotations and schema cover the remaining context, making it adequate for a basic calculator.

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 input schema fully describes both parameters ('Total cost' and 'Impressions'), and the description adds no extra meaning beyond what is already in the schema. With schema description coverage at 100%, the baseline score 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 'Calculate' and clearly identifies the resource as 'Cost per 1,000 impressions (CPM).' This distinguishes it from sibling calculator tools like cpc-calculator and ctr-calculator by naming the exact metric, leaving no ambiguity about the tool's function.

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 implies usage for computing CPM but provides no explicit guidance on when to choose this over other calculators or any exclusions. Since the tool name and description are self-explanatory, the usage context is implied rather than stated.

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