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

Annotations (readOnlyHint, idempotentHint, openWorldHint) already cover safety and idempotency. The description adds the three rate types but introduces the ambiguous '($0.001 USDC)' element—possibly a per-call cost—without explanation. It doesn't contradict annotations but also doesn't clarify the fee or response behavior.

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 a single sentence, front-loaded with the core action and resource. It's efficient but the parenthetical is cryptic and could be omitted or clarified. No wasted words otherwise.

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?

For a simple read-only tool with full schema coverage and annotations, the description covers the basics. However, it leaves the fee/currency ambiguity unresolved and doesn't mention geographic scope (ZIP implies US but not explicit). The output schema exists, so return format isn't required, but the missing fee clarity is a gap.

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 each parameter is already described in the schema. The tool description adds no additional parameter semantics (e.g., format constraints, range, or interplay between weight and ZIPs). Baseline 3 applies.

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 clearly states the verb 'Calculates' and the resource (shipping rates) with specific service types (ground, priority, express). It distinguishes from siblings by being the only shipping-rate tool. However, the parenthetical '($0.001 USDC)' is ambiguous—whether it's a fee or a currency unit—which slightly muddies the purpose.

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?

No guidance on when to use this tool vs alternatives. It doesn't mention prerequisites (e.g., US-only ZIPs), limitations, or when not to use it. Given the sibling list includes unrelated estimators, there's no exclusion or routing context.

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