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

Annotations already convey a safe read-only, idempotent operation. The description adds valuable behavioral details beyond that: results are in integer cents, both rounding totals and their exact discrepancy are reported, malformed lines throw, and mixing rounding methods is prohibited. No annotation contradiction exists.

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?

A single front-loaded sentence states the core operation immediately and earns its length by adding constraints and failure behavior with no filler.

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?

There is no output schema, but the description names the key output qualities (integer cents, discrepancy) and failure behavior, and the input schema fully covers parameters. It stops short of specifying the exact return shape/field names, which would make it fully complete.

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%, so the schema already documents lines, rounding, and taxInclusive. The description adds the GST-free and rounding-method context but does not add parameter-level details; with the schema carrying the full burden, a baseline 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 ('Total'), names the resource (multi-line invoice), and states the scope (handles GST-free lines, ATO rounding methods, discrepancy reporting). It clearly distinguishes this from sibling GST/payroll tools by focusing on invoice total computation rather than allowances or GST calculation.

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 the main use case and imposes a constraint ('an invoice must not mix them'), but it does not explicitly state when to prefer this tool over the sibling calculate_gst or other related tools, and offers no exclusions.

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