Great question! Because some apps have custom fields, it's not always easy to know beforehand what fields will be available in each step of your Zap. The best way to know for sure is to do the following

1. Connect the apps to your Zap
2. Test your Trigger step for a sample to view the fields that come over within that sample
3. Check out the template in your action step and click on the "refresh fields" button near the bottom of the action template to see if that helps pull in any additional fields

Sometimes, your Trigger sample will only show certain fields if you didn't fill out all available fields on the sample you tested with. When creating a new record of sorts, it's always a good idea to fill out all fields to ensure they show up in your Zap.

Alternatively, if you're comfortable looking at API documentation, most will list available fields.

Note: While most available fields are supported on Zapier, this isn't the case 100% of the time. If you come across a field that is available through the app's API but isn't available through Zapier, please email our support team at contact@zapier.com so they can log the request for you.