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

Annotations already mark it read-only, idempotent, non-destructive, and closed-world, but the description adds critical behavior: incomplete scenarios return needs_input with no numeric comparison, and complete scenarios return contribution, maximum CPA, and ROAS. It also enforces a strict null-vs-zero/default-currency rule for unknown inputs. This goes well beyond what annotations provide.

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 four tight sentences with no filler. It front-loads the scope, then covers input rules, incomplete-scenario behavior, complete-scenario output, and exclusions. Every sentence earns its place.

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 nested input schema and existing output schema, the description covers the key scope, input constraints, and return behavior for incomplete versus complete scenarios. It does not explain return fields, which is acceptable because an output schema exists. The main gap is explicit routing away from sibling tools like calculate_break_even_roas.

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 adds aggregate constraints such as two-to-five scenarios and one currency, plus a strong null handling rule. However, the schema already contains detailed field-level descriptions for the nested inputs, so the description mostly repeats or summarizes those semantics rather than adding new per-parameter meaning. This is adequate but not rich.

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 states a specific verb and resource: compare two to five pricing or cost scenarios in one currency. It also clarifies the outputs (contribution, maximum CPA, ROAS) and exclusions, so an agent can distinguish it from general marketing tools. It does not explicitly name a sibling alternative, which keeps it below a perfect score.

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 gives clear usage context: two to five scenarios, unknown inputs must be null, and incomplete scenarios must prompt labeled questions. It also states what the tool does not do, such as predict sales or change pricing or advertising. However, it does not name an alternative like calculate_break_even_roas, so the when-to-use routing is not fully explicit.

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