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

Annotations already cover read-only, idempotent, non-destructive, and closed-world behavior. The description adds important error behavior beyond annotations: malformed input returns an {"error": ...} object instead of a protocol error, and retry after correction is safe.

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 purpose is front-loaded and the usage and error guidance are easy to scan. The full input/output example is useful but somewhat verbose, especially since an output schema exists.

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 a computation tool with complete schema documentation, rich annotations, and an output schema, the description supplies the remaining operational context: usage boundaries, error contract, and retry safety.

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 coverage is 100%, and the schema already documents tax_pct, discount_pct, and the line_items shape including the 100-item cap. The description's input example is helpful but largely illustrates rather than adding new parameter semantics beyond the schema.

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: totals an invoice and enumerates the exact components computed (per-line totals, subtotal, discount, tax, grand total). It clearly distinguishes itself from processor_fees and installment_plan by naming those siblings as out of scope.

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?

Explicitly says when to use it: several line items rolling up with discount and tax. It also names two alternatives and the conditions that select them, so an agent has direct routing guidance.

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