Shipping Rates & Postage Calculator
Server Details
Live USPS, UPS & FedEx shipping rates plus USPS postage and stamp prices. Free, no API key.
- Status
- Healthy
- Last Tested
- Transport
- Streamable HTTP
- URL
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Tool Definition Quality
Average 4.8/5 across 2 of 2 tools scored.
The two tools are clearly distinct: one handles postage for letters/envelopes/postcards via USPS First-Class, while the other handles shipping rates for packages via multiple carriers. The descriptions explicitly state scope and point to the other tool when the item is a package vs. a letter.
Both tools follow a consistent verb_noun pattern: get_postage_price and get_shipping_rates. The naming is descriptive and predictable.
With only two tools, the server is minimal but covers the core functions of postage and shipping rate calculation. However, additional tools for tracking or international letter postage might be expected, making the count feel slightly thin.
The tools cover the primary use cases: postage for domestic letters and shipping rates for packages domestically and internationally. A notable gap is the lack of international letter postage rates, but the descriptions are thorough and include important details like stamp combinations and discounted rates.
Available Tools
2 toolsget_postage_priceGet USPS postage priceARead-onlyInspect
Get the current USPS First-Class postage price for a letter, large envelope (flat), or postcard mailed within the US — including how many Forever stamps to put on it and an exact combination of stamp denominations that covers the postage with no waste. Prices are zone-independent (same anywhere in the US). For boxes and parcels use get_shipping_rates instead.
| Name | Required | Description | Default |
|---|---|---|---|
| ounces | No | Weight in ounces (default 1; max 3.5 for letters, 13 for large envelopes) | |
| mail_class | Yes | What is being mailed |
Tool Definition Quality
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already indicate readOnlyHint true, and description adds that prices are zone-independent and provides stamp combination details. No contradictions; description enriches behavioral understanding beyond annotations.
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?
Two sentences only, front-loaded with purpose, then immediately provides scope, limitations, and sibling reference. Every sentence adds value, no redundancy.
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?
Given the tool's low complexity (2 params, simple enum), the description covers purpose, usage scope, result details (stamps), and alternative. No output schema needed as result is explained. Complete and sufficient.
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?
Input schema has 100% coverage with descriptions, so baseline is 3. The tool description adds no new parameter-specific information beyond what is in the schema. However, it does explain the overall result (stamp combinations) which is contextual.
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?
Clearly states the tool gets USPS postage price for specific mail types (letter, large envelope, postcard) and includes stamp recommendations. Explicitly distinguishes from sibling tool get_shipping_rates by stating it is for boxes and parcels.
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?
Explicitly says when to use: for letters, envelopes, postcards within US. Also says when not to use: 'For boxes and parcels use get_shipping_rates instead.' Provides clear context and alternative.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
get_shipping_ratesGet package shipping ratesARead-onlyInspect
Get live USPS, UPS, and FedEx shipping rates for a package from a US ZIP code to a US or international destination. Returns carrier, service, price in USD, and estimated transit days, sorted cheapest first. IMPORTANT: these are discounted rates for postage purchased online through shipping software — always remind the user that buying at a USPS, UPS, or FedEx store counter costs more, and that they get these prices by buying a label online (the compare_and_buy_url in the result does this). Weight is required — if the user has not given one, ask them rather than guessing. Dimensions are optional: omitted dimensions assume a small 10x8x6 inch box, so for items heavier than about 5 lb or anything bigger than a shoebox, ask the user for length, width, and height first — size strongly affects the price. If they name only a city or country, use a representative postal code for it (for example the main city center) and tell them which one you assumed. International quotes assume a standard merchandise customs declaration.
| Name | Required | Description | Default |
|---|---|---|---|
| to_zip | Yes | Destination postal code: 5-digit ZIP for US, local postal code format otherwise (e.g. M5V 2T6 for Toronto) | |
| weight | Yes | Package weight | |
| from_zip | Yes | Origin US ZIP code (5 digits). Quotes are US-outbound only. | |
| width_in | No | Package width in inches (optional) | |
| height_in | No | Package height in inches (optional) | |
| length_in | No | Package length in inches (optional) | |
| to_country | No | Destination country as a 2-letter ISO code (default 'US') | |
| weight_unit | No | Unit for weight, 'oz' or 'lb' (default 'lb') |
Tool Definition Quality
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
The description explains behavioral details beyond readOnlyHint: returns discounted rates, sorted cheapest first, includes compare_and_buy_url. It clarifies assumptions (dimensions default, customs declaration). No contradiction with annotations.
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 thorough but slightly long. However, every sentence is valuable, and key points are front-loaded. It could be trimmed slightly, but structure is logical and clear.
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?
Despite lacking output schema, the description lists return fields (carrier, service, price, transit days) and provides all necessary context for correct invocation, including edge cases and reminders.
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%, but description adds critical context: weight is required and must be asked; dimensions are optional with a default box size; to_zip format for international; to_country default. It compensates fully for any schema gaps.
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 tool 'Get live USPS, UPS, and FedEx shipping rates' with specific scope (from US ZIP, domestic or international). It distinguishes from sibling 'get_postage_price' by focusing on live rates from three carriers. The verb 'get' and resource 'shipping rates' are precise.
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 provides explicit when-to-use and how-to-use guidance: ask if weight missing, remind user of discounted pricing, ask dimensions for larger items, use representative postal codes for cities/countries. It also tells what to do when input is vague.
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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