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

Annotations (readOnlyHint=true, openWorldHint=false) correctly signal a pure, non-destructive computation, and the description adds substantial context beyond them: the exact return shape, a per-call credit price with the CAD-cent conversion, and the failure-billing rule (schema-invalid input is rejected before billing). That billing edge case is exactly the kind of thing an agent cannot infer from the structured fields.

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?

Three sentences, front-loaded with the operation, then the return contract, then commercial terms. Nothing is redundant, and the long return-field enumeration earns its length because no 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?

There is no output schema, and the description fully compensates by listing every returned field. Combined with the billing rule and the 'no customer details' scope note, an agent has everything needed to invoke it correctly and predict what comes back.

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 explains qty, sku truncation, unitCents, depositPct and discountPct with ranges and defaults. The description restates that a discount and HST are applied but adds no semantics the schema lacks — notably it never states what HST rate is used, though 'rate' appears in the return list.

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 concrete verbs (totals, applies, computes) against a concrete resource (line items, discount, HST, deposit) and enumerates the exact output fields. The scope line 'No customer details taken' draws a clear boundary that separates it from an invoicing tool, and the compounding of discount + HST + deposit makes it read as the full calculator vs. the narrower hst-calc sibling.

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?

Usage is implied by 'totals line items... computes a deposit' — you call it when you need a priced quote. But there is no explicit when-to-use or when-not statement, and the sibling hst-calc (HST-only) is never named as the alternative for a simpler calculation.

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