SyncFolder — Desktop User Guide

Mobile Access and Sharing

Mobile Access and Sharing lets Android and iOS devices running the SyncFolder mobile app connect securely to your Windows PC and exchange files — without a third-party cloud service in between. Your files stay on your machine; only paired, authorised devices on the same local Wi-Fi network can reach them.

Instead of manually configuring complex network sharing (SMB) in Windows Explorer, you can simply add folders here and access them directly within the SyncFolder Android app.

  • Easy Setup: No need for Windows user permissions or NAS configurations.
  • Bidirectional: Use your mobile device to upload or download files directly to these folders.
  • Fast & Secure: Works over your local network for high-speed synchronization.

Tip: Use this as a lightweight alternative to the "NAS" option in the Android app. Just add a folder, start the service, and find it on your mobile device.

⚠ Local network only. Mobile Access and Sharing works exclusively when your PC and mobile device are connected to the same local Wi-Fi network. Access over the internet or mobile data is not supported.

How it works

When Mobile Access and Sharing is active, SyncFolder starts a lightweight HTTPS file server on your Windows machine using the Kestrel web server. Kestrel automatically selects a free available port — there is nothing to configure. A self-generated TLS certificate is created automatically — no external certificate authority is required. All traffic between your mobile device and your PC is encrypted end-to-end. After the initial pairing handshake, every subsequent request is validated with a secure session token, so credentials are never sent in the clear.

Once pairing is complete, the mobile app locates your PC automatically using mDNS (Multicast DNS). This means you never need to look up or type an IP address — as long as both devices are on the same Wi-Fi network, the app finds the file server on its own, on whatever port it is using.

ⓘ What is mDNS? Multicast DNS is a zero-configuration protocol that allows devices on a local network to discover each other by name without a central DNS server. SyncFolder advertises the file server via mDNS so the mobile app can find it even if your PC's IP address changes (e.g. after a router restart).
ⓘ Firewall note. Kestrel picks a free port automatically each time it starts. If Windows Firewall prompts you to allow access when you first enable this feature, click Allow. Allowing SyncFolder by application name (rather than by a fixed port number) ensures the firewall rule remains valid across restarts.

Prerequisites

  • SyncFolder for Windows is installed and running.
  • SyncFolder for Android or iOS is installed on the mobile device.
  • Both the PC and the mobile device are connected to the same local Wi-Fi network.
  • At least one shared folder has been configured (see below).

Configuring shared folders

Before mobile devices can access any files, you must define which folders are available for sharing. Each share is a named entry that maps a display label to a physical folder path on your PC. Shared folders are the only server-side setting available — everything else is handled automatically.

Adding a shared folder

1
Open the Mobile Access and Sharing page from the left-hand navigation bar.
2
Under Shared Folders, click Add Share.
3
Enter a Share Name — this is the label mobile users will see (e.g., Documents, Projects, Media).
4
Click Browse and select the folder on your PC you want to share.
5
Click Save. The share appears in your list immediately.
✓ Tip. Use descriptive share names that mean something to your mobile users. The folder's actual path on disk is never shown to mobile devices — only the share name is visible.

Shared folders at a glance

Field Required Description
Share name Required The friendly label displayed to mobile devices. Must be unique across shares. Accepts letters, numbers, spaces, and hyphens.
Folder path Required An absolute path to an existing folder on the local drive or a mapped network drive accessible to SyncFolder.
⚠ Be selective with shared folders. Any paired mobile device can read and write files within a shared folder. Avoid sharing root drives or folders that contain sensitive system files.

Removing a shared folder

In the Shared Folders list, click the remove icon next to the share you want to delete, then confirm. The share entry is removed immediately; files on disk are not affected. Paired devices lose access to that share instantly.

Pairing a mobile device

Before a mobile device can connect, it must complete a one-time pairing process. Pairing uses a time-limited QR code so no passwords need to be typed or exchanged manually.

On your Windows PC

1
Go to Mobile Access and Sharing.
2
Locate the Pair a New Device section. A QR code is displayed automatically.
3
The QR code is valid for 5 minutes. After expiry it refreshes automatically — just wait for the new code.

On the mobile device

1
Open the SyncFolder app on your Android or iOS device.
2
Select or create a backup/sync task with a storage location set to Local Windows computer, tap Windows computer and select the computer that appears in the list.
3
When the Scan QR Code page appears point your camera at the QR code shown on your PC.
4
After a successful scan the app connects automatically and lets you select a folder from the available shares.
ⓘ What the QR code contains. The code encodes a short-lived pairing token. Once pairing completes, a long-lived secure session token replaces the pairing token — the QR code itself cannot be reused. On all subsequent connections the mobile app uses mDNS to locate the server and its current port automatically.
⚠ Keep the QR code private. Anyone who scans it within the 5-minute window — and is on the same local network — can pair their device to your PC. Only display the pairing page when you are ready to pair a trusted device.
Scenario A
Normal pairing
Phone and PC on the same Wi-Fi. Open the pairing page, scan the code, and you are done. The mobile app will locate the PC via mDNS on every subsequent connection.
Scenario B
QR code expired mid-scan
The page auto-refreshes with a new code every 5 minutes. Simply tap Scan QR Code again on the mobile app and scan the new code.
Scenario C
PC gets a new IP address
No action needed. Because the mobile app uses mDNS for discovery, it finds the PC's updated address and port automatically on the next connection attempt.

Managing paired devices

All devices that have successfully paired are listed in the Paired Devices section of the Mobile Access and Sharing page. Each entry shows the device name (as reported by the mobile OS) and the date it was paired.

Column Description
Device name The friendly name reported by the mobile device (e.g., "Ana's iPhone", "Galaxy S24").
Platform Android or iOS, shown as a small icon.
Paired on Date and time the pairing was completed.
Last seen Date and time of the most recent connection from this device.
Actions A remove button to revoke access for this device immediately.

Removing a paired device

Click the remove icon next to a device and confirm the prompt. The device's session token is immediately invalidated. The next time that device attempts to connect, it will receive an authentication error and must be re-paired to regain access.

✓ Tip. If you lose a device or suspect unauthorised access, remove it from this list straight away. Its token is revoked server-side — no action is required on the mobile device itself.

Security overview

Layer Mechanism Detail
Transport HTTPS / TLS All traffic is encrypted using a self-generated certificate created at first run. The certificate is pinned in the mobile app during pairing.
Pairing Time-limited QR token The pairing token embedded in the QR code expires after 5 minutes and is single-use. A new one is generated automatically.
Session Secure bearer token After pairing, every API request carries a signed session token. Tokens are stored securely in the app's keychain / keystore.
Network scope Local Wi-Fi only The file server is reachable only within the local network. No internet exposure is possible.
Access scope Shared folder list Mobile devices can only browse and transfer files within explicitly configured shared folders. The rest of your file system is not reachable.
Revocation Per-device removal Removing a device immediately invalidates its token. No further access is possible until the device re-pairs.
ⓘ Self-signed certificate warning on mobile. Because the certificate is self-generated rather than issued by a public CA, the SyncFolder mobile app uses certificate pinning during pairing to establish trust. You may see a brief "untrusted certificate" notice on first connection; this is expected and safe to proceed.

Troubleshooting

Mobile device cannot find the PC after scanning

  • Confirm both devices are on the same local Wi-Fi network — this is required for the feature to work.
  • Check that Windows Firewall is not blocking SyncFolder. In Windows Defender Firewall → Allow an app through Windows Firewall, verify SyncFolder is listed and checked for Private networks. Because Kestrel selects its port automatically, the firewall rule must allow the application by name rather than by a specific port number.
  • Some routers have AP isolation (also called client isolation) enabled, which prevents devices on the same Wi-Fi from communicating with each other. Check your router settings and disable AP isolation if present.
  • mDNS relies on multicast traffic on the local network. If your router or security software blocks multicast, the mobile app will not be able to discover the PC automatically. Check that multicast is enabled on your router.
  • Try disabling your VPN — many VPN clients block local network traffic and mDNS multicast.

QR code expires before I can scan it

  • The code refreshes automatically every 5 minutes. Wait for the new code to appear, then scan without delay.
  • Ensure the Mobile Access and Sharing page remains in the foreground on your PC while scanning — navigating away does not pause the timer.

A paired device shows "Authentication error"

  • The device's session token may have been revoked, or the server certificate may have been regenerated. Remove the computer entry from the mobile app and repeat the pairing process.

Slow transfer speeds

  • Performance depends on your local network. For best results, connect your PC via Ethernet and keep the mobile device close to the Wi-Fi access point.
  • Large files transferred over a 2.4 GHz Wi-Fi band will be noticeably slower than on 5 GHz or Wi-Fi 6.

Last updated: May 14, 2026