# Field Mappers with JSON Forms

Your customers will come to you with custom third-party configurations. One customer may store their Lead information in a vanilla Salesforce **Lead** object, another might customize the **Lead** object with additional custom fields, and a third might use an entirely custom `my_lead__c` record type to store their Lead information.

You need to know where your users are storing their data, and which of their fields map to fields in your app. A field mapper JSON Forms data source allows you to prompt your users to map fields between your app and their third-party system, and then reference those mappings in your flows.

If you have not yet, we strongly recommend reviewing [Dynamic Data Sources](https://prismatic.io/docs/get-started/build-integrations/dynamic-data-sources.md) and [Intro to JSON Forms](https://prismatic.io/docs/get-started/build-integrations/json-forms-intro.md) before watching this video.

**Also See:**

* [Prismatic VS Code Extension](https://prismatic.io/docs/dev-tools/vscode-extension.md) that we used in this video
* [JSON Form validation](https://prismatic.io/docs/integrations/data-sources/json-forms/form-validation.md) to learn how to add validation to your JSON Forms