Swantide's data transfer tool (https://app.swantide.com/transfer) offers some nice benefits over the native Salesforce Data Loader (https://dataloader.io/), primarily through surfacing potential errors in the upload and making it easier to correct them.

Currently, Swantide's data transfer tool supports updates and uploads for the Account, Contact, Opportunity, and Lead objects. Custom objects and upserts need to be handled through the Data loader.

Step 1: Log into Dataloader using your Salesforce credentials

Step 2: Select the file that you will be uploading, as well as the object and action you'll be performing

Step 3: Map fields from your CSV to Salesforce fields

Note that Dataloader will attempt to map fields automatically if there is an exact match, but is not always successful. Keep in mind the required fields for each object. You may need to edit your file to have all required fields, particularly if doing an upsert. See this guide for more information on upserts.

If there is an error in any of the records, they will not be uploaded to Salesforce, and the tool will provide you with a list of the failed records and the error reason. Download the file, correct the errors, and re-upload again.