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

Annotations already declare readOnly/idempotent/non-destructive/openWorld=false, so safety is covered. The description adds real behavioral value beyond that: the tiering rules and 才數 formula, region-dependent pricing with outer-island caveat, and the disclaimer that actual cost is subject to HCT's physical measurement. It doesn't describe pagination/response shape, but that is minor here.

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?

Purpose and tier table are front-loaded, then a clearly marked 用法 block, then the disclaimer. Dense but every segment carries operational information. The tier/roof-of-charge listing is long, but it is load-bearing rather than 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?

An output schema exists so return values need not be explained. Given the tool's complexity (tiered pricing, region variance, multiple invocation modes), the description covers all modes, the class thresholds, the formula, and the accuracy caveat. Nothing an agent needs to call it correctly is missing.

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%, so baseline would be 3, but the description adds cross-parameter semantics not in the schema: the requirement that length/width/height be supplied together, that weight alone can determine a class, and that city must use official county names. These interaction rules genuinely extend the per-field schema docs.

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+resource (試算超材費) and narrows the scope precisely (台灣國內最後一段配送, 新竹物流宅配, 桃園所出發). It also pins the domain to the 0523.tw/c official implementation, which an agent can use to distinguish it from siblings like lucky_freight_quote.

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 用法 section explicitly describes three invocation modes: no params → rate table, L/W/H (+optional weight/city) → precise estimate, weight-only → weight-based class. That is clear when-to-use guidance for each mode. It does not, however, route the agent away from or toward any sibling tool, so it stops short of 5.

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