Comparison
ShipStation Rate Shopper does not compare package types. What can?
Rate Shopper compares services for the package already on the order. It does not try other package types or boxes. ShipStation's help article says it "only compares services. It does not compare different package types." So the box has to be chosen before Rate Shopper runs.
What people do today
- Product defaults and automation rules
- ShipStation can set a package from a product's defaults or from a rule that matches a SKU, tag, or weight. That works when one SKU always ships in one box. Rules that match Item SKU only apply to orders with a single unique line item, and no native rule works out which of your boxes a mixed cart fits.
- Picking the box by hand
- A packer chooses the box, enters its size, and rates the order again. ShipStation runs its rules, Rate Shopper included, when an order imports and when you click Reprocess Automation Rules, so a changed box is not re-rated on its own.
- A script against the ShipStation API
- The script has to read product dimensions, choose a box, and write the size back. API writes do not re-run Rate Shopper, so it also has to rate the order itself. ShipStation's order write replaces the whole order, so a careless write resets fields set elsewhere.
What ShipExtension does
- It picks the box from your own box list. The smallest box that fits wins, which is also the one with the lowest dimensional weight.
- Every unit has to fit the box in three dimensions, turned any way, and the box has to hold their combined volume. It is a fit check, not a full packing simulation. When ShipStation lists a kit with its component items, the components are what get fitted.
- It writes the box size and weight to the order. If the box is linked to one of your ShipStation custom packages and a ShipStation V2 API key is connected, it sets that package instead.
- Then it rate shops that box across your connected carrier accounts and writes the lowest-cost eligible service back.
- It does not rate every box on your list, and it does not quote carrier flat-rate packaging. The one option is FedEx One Rate: a rule can also quote FedEx 2Day in the smallest One Rate box the order fits, as one more candidate. This also needs a V2 API key.
Rate Shopper and ShipExtension, side by side
| Feature | ShipStation Rate Shopper | ShipExtension |
|---|---|---|
|
Compares services and carriers |
Yes. Compares live rates and picks a service, with Best Value, Cheapest, and Fastest defaults. | Yes. Compares live rates across your connected carrier accounts and writes the lowest-cost eligible service. |
|
Tries other package types |
No. It rates the package already on the order. ShipStation notes a narrow exception for custom package types in Australia and New Zealand. | Not by rate. It picks the smallest of your boxes that fits, then rates that box. FedEx One Rate can be added as one more candidate. |
|
Chooses a box for a multi-item order |
No. Native rules set a package by SKU, tag, or weight, and SKU rules only apply to single-line-item orders. | Yes. Each unit must fit in three dimensions and the box must hold the combined volume. Listed kit components are fitted, not the kit row. |
|
Writes the box to the order |
No. The package has to be set before it runs. | Yes. Writes the size and weight, or your linked ShipStation custom package when a V2 API key is connected. |
|
Runs again after the order changes |
At import and when you click Reprocess Automation Rules. Changes made through the API do not re-run it. | Your rules run on new orders and on scheduled runs over orders awaiting shipment. |
FAQ
Frequently asked questions
- Does ShipStation Rate Shopper compare package types?
- No. ShipStation's help article says it only compares services and does not compare different package types. It rates the package already on the order. ShipStation notes a narrow exception for custom package types in Australia and New Zealand.
- Does Rate Shopper run again after an app changes the box?
- No. ShipStation runs its automation rules, Rate Shopper included, when an order imports and when you click Reprocess Automation Rules. A change made through the API does not trigger them.
- Does ShipExtension rate every box on my list?
- No. It picks the smallest box that fits, which is also the box with the lowest dimensional weight, and rate shops that box. It does not quote carrier flat-rate packaging, except FedEx One Rate when you turn it on in the rule and a V2 API key is connected.
- How does ShipExtension handle multi-item orders and kits?
- Each unit has to fit the box in three dimensions and the box has to hold their combined volume. When ShipStation lists a kit with its component items, the components are fitted instead of the kit row.
- Do I have to leave ShipStation?
- No. ShipExtension works through the ShipStation API. Your orders, carriers, and labels stay in your ShipStation account.
ShipStation behavior is cited from its Rate Shopper help article and automation-rules criteria article as of July 2026, and from our own API testing in September 2026.
Pick the box first, then the rate.
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