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Action Tags Mobile App

Action Tags — Mobile App Action Tags

Article ID RC-AT-11 — Action Tags: Mobile App Action Tags
Domain Action Tags
Applies To REDCap Mobile App only; requires Project Design and Setup rights
Prerequisite RC-AT-01 — Action Tags: Overview; REDCap Mobile App must be installed and project initialized
Version 1.0
Last Updated 2026
Author See KB-SOURCE-ATTESTATION.md
Related Topics RC-AT-01 — Action Tags: Overview; RC-AT-02 — @HIDDEN & @READONLY — Visibility Control — @HIDDEN & @READONLY

1. Overview

REDCap provides five action tags designed exclusively for use in the REDCap Mobile App. This article covers three of them (@BARCODE-APP, @APPUSERNAME-APP, @SYNC-APP), which extend mobile data collection with barcode/QR scanning, automatic capture of the mobile user's identity, and syncing of uploaded images from the server to the app. The remaining two (@HIDDEN-APP and @READONLY-APP) are documented in RC-AT-02 — @HIDDEN & @READONLY — Visibility Control.

Mobile App only. All three tags in this article function only within the REDCap Mobile App. They have no effect on browser-based data entry forms or survey pages.

2. @APPUSERNAME-APP

Sets a field's value to the app username of the person currently using the mobile app. The app username is the credential used to log in to the mobile app, which may differ from the user's REDCap server username.

This is the mobile equivalent of @USERNAME (which captures the REDCap server username). Use @APPUSERNAME-APP when you need to identify who entered data in the field via the app specifically.

Applies to: Text Box fields.

Syntax (no parameters):

@APPUSERNAME-APP

Note: If the same field has @USERNAME and @APPUSERNAME-APP, they will conflict. Use the appropriate tag for the context in which data will be collected (browser vs. mobile app), or use @USERNAME for browser-based entry and keep @APPUSERNAME-APP on a separate field.

3. @BARCODE-APP

Enables the device's camera to capture a barcode or QR code value and store it in the tagged field. When the user taps the field in the mobile app, a scan button appears. Activating it opens the camera; once a code is detected, the decoded value is stored in the field automatically.

Applies to: Text Box fields.

Syntax (no parameters):

@BARCODE-APP

Common uses: Scanning participant wristbands, specimen labels, drug vials, or equipment tags to capture identifiers without manual typing — reducing transcription errors in field or clinical settings.

Camera permission required. The device must grant the REDCap Mobile App permission to access the camera before scanning can occur. If permission is denied, the scan button will not function.

4. @SYNC-APP

When a project is initialized in the REDCap Mobile App and a File Upload or Signature field has @SYNC-APP, any image files uploaded to a record on the REDCap server will be sent down to the app so they are viewable when editing that record offline.

Without this tag, images uploaded via the browser are not automatically pushed to the app — users in the field would see the field but not the image content.

Applies to: File Upload fields and Signature fields.

Syntax (no parameters):

@SYNC-APP

Common uses: Making reference images (e.g., body maps, consent forms, photo IDs) available to field staff who collect data offline via the app.

Storage consideration: Syncing images increases the amount of data downloaded to each device during synchronization. In projects with many large files, this can slow sync times and consume significant device storage.

5. Common Questions

Q: Do mobile app action tags do anything on browser-based forms or surveys?

A: No. @APPUSERNAME-APP, @BARCODE-APP, and @SYNC-APP are all silently ignored when a form is opened in a web browser.

Q: What is the difference between @USERNAME and @APPUSERNAME-APP?

A: @USERNAME captures the REDCap server username (the login used on the REDCap website). @APPUSERNAME-APP captures the username used to log in to the mobile app, which is set up separately and may be different. In some configurations both usernames are the same, but they are not guaranteed to match.

Q: Can @BARCODE-APP store any type of barcode format?

A: The REDCap Mobile App supports standard 1D barcodes (UPC, EAN, Code 128, etc.) and 2D codes (QR codes, Data Matrix). The decoded value is stored as a text string regardless of format.

Q: If I use @APPUSERNAME-APP and also @USERNAME on the same field, what happens?

A: This creates a conflict. The field cannot store both usernames simultaneously. Avoid combining them on the same field. Instead, use @USERNAME on a separate field for web-based entry and @APPUSERNAME-APP on a different field for mobile app entry.

Q: Does @SYNC-APP work offline, or do images need to be present before syncing?

A: Images must be uploaded to the REDCap server first (via web or another app user). When a mobile device syncs with the server, @SYNC-APP pulls server-side images down to the app so they are available for viewing when working offline. The tag does not affect images uploaded from within the mobile app itself.

6. Common Mistakes & Gotchas

Expecting mobile app tags to work in the browser. These tags have no effect outside the REDCap Mobile App. Confirm that data collection actually occurs via the app before adding these tags.

Using @SYNC-APP on non-image file types. The tag is designed for image and signature files. Behavior with other file types (PDFs, Word documents, etc.) may be unpredictable or files may not sync as expected.

Not accounting for increased sync time with @SYNC-APP. In projects with many records and large attached images, enabling sync can significantly extend the time required to synchronize the app with the server, particularly on slow connections.