Calculates ground, priority, and express shipping rates ($0.001 USDC)
| Name | Required | Description | Default |
|---|---|---|---|
| originZip | Yes | Origin 5-digit ZIP code | |
| weightLbs | Yes | Parcel weight in pounds | |
| destinationZip | Yes | Destination 5-digit ZIP code |
| Name | Required | Description | Default |
|---|---|---|---|
| success | Yes | Estimation status | |
| ratesUSD | Yes | USPS rate estimates |
Changes observed during successful MCP inspections.
Input schema / properties / destinationZip / descriptionAdded value: +"Destination 5-digit ZIP code"Input schema / properties / originZip / descriptionAdded value: +"Origin 5-digit ZIP code"Input schema / properties / weightLbs / descriptionAdded value: +"Parcel weight in pounds"Output schema / (root)Previous value: -nullNew value: +{
+ "properties": {
+ "ratesUSD": {
+ "description": "USPS rate estimates",
+ "type": "object"
+ },
+ "success": {
+ "description": "Estimation status",
+ "type": "boolean"
+ }
+ },
+ "required": [
+ "success",
+ "ratesUSD"
+ ],
+ "type": "object"
+}Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly, idempotent, non-destructive behavior. Description adds the $0.001 USDC cost detail, which is useful context beyond annotations, but does not explain rate determination or output structure.
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?
Single, front-loaded sentence with zero waste. Price detail in parentheses is relevant and concise.
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?
Output schema exists, so return values need not be explained. Description covers what the tool does, pricing, and tiers; only usage context and rate methodology are absent, which is minor given the schema and annotations.
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 parameters are fully documented. Description adds no parameter details, making the baseline 3 correct.
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 (calculates shipping rates) and names the three tiers (ground, priority, express). It does not differentiate from siblings, but no sibling overlaps, so 4 is appropriate.
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?
Implies use for shipping rate estimation but gives no when-to-use guidance, no prerequisites, and no alternatives. Adequate but minimal.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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