To take full advantage of the Mass Create feature, the CSV that you upload has to be formatted properly, and be as concise as possible. There are a few brief questions to ask before uploading any CSV:

Question One: Is there any erroneous data outside of the main body of data in the CSV?
If there is any data outside of the main block of data, that will create issues with the Mass Create tool. At best, the CSV upload will take much longer than necessary; at worst, the upload will fail or timeout. To avoid this, make absolutely certain to right-click + delete all rows outside of the main body of data. Even if it appears that your data is clean, it always pays to double check.

Note: In Microsoft Excel, the scroll bar will end at the last data point in any spreadsheet. If the scroll bar on the right side of your screen is able to travel past the last row of the CSV, that indicates there is some kind of data further down the sheet the needs to be deleted. The easiest way to clear this out is to highlight all rows beneath the last, and right click + delete them.

Question Two: Have I deleted all columns that are not going to be used in this Mass Create?
Any CSV that has been freshly exported will contain a number of columns that should be removed from the CSV before it is uploaded using the Mass Create tool. The column headers required for common import functions are outlined below

Note: If your CSV contains information from multiple categories, you **must* include the Category column header for the Mass Create to work. Conversely, if your CSV contains information from only a single category, you should remove the Category column entirely and select the category on the Mass Create page instead.

Column Headers for Common Mass Create Actions:

Quantity Adjustment for Magic Singles
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Required column headers: 4
​Substitute "Add Qty" for "Qty" in this CSV to increment quantities instead of reset them.

Sell or Buy Price Adjustment
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Required column headers: 3

Question Three: Have I deleted all rows that are not going to be used in this Mass Create?
It is also beneficial to remove rows that are not making any changes in your CSV. Lets say, for example, that we are updating an existing CSV with the column header "Add Qty." Any product with an Add Qty of 0 is not going to make any changes to quantity, but the system will have to parse these rows regardless of whether a change is made or not. Removing them can dramatically increase your upload speed.

To remove these products, highlight all columns of your CSV in Excel, and in the Data tab, click Sort. In this example, we will choose to sort by "Add Qty" and Highest to Lowest. You can now see where the first line item with a 0 in the Add Qty field is, and can delete all lines with a 0 this column quickly and easily.