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CullKit vs Synology Photos: Which App for Culling?

By Ingo D ·

Your Synology NAS came with Synology Photos pre-installed and ready to go. It organises your library by faces, subjects, places, and dates. It gives you a mobile app for browsing your photos from anywhere, and a web interface for managing albums from your desktop. For viewing and organising a family photo collection, it does exactly what it promises.

But if you are a photographer who shoots in volume, weddings, events, portrait sessions, or travel, you know that organising is only half the job. Before you organise, you cull. You take 1,600 frames from a Saturday wedding and get them down to 120 keepers before you reach for an editing slider. That process, the first-pass triage every shoot-heavy photographer performs after every job, is where Synology Photos stops and CullKit begins.

What does Synology Photos do well?

Synology Photos is a capable photo library manager. For the task it was built for, browsing, organising, and sharing a personal photo collection, it delivers a solid feature set.

It sorts images by faces, detects subjects and scenes, arranges them on a timeline, and lets you create albums for sharing with family or clients. The mobile app mirrors the web experience and works over QuickConnect when you are away from home. The interface is clean, the setup is automatic if you use the default photo share, and the whole system runs on hardware you already own. Nothing is uploaded to a third-party cloud.

For a home user managing smartphone uploads and family snapshots, Synology Photos is the right tool. It was never designed to be a working photographer’s culling station.

Where does Synology Photos fall short for culling?

Three gaps make Synology Photos unfit for a professional culling workflow.

No rating system. Synology Photos does not support star ratings. There is no 1-to-5 scale you can apply to a frame, no reject flag you can raise, no colour label you can assign. The metadata vocabulary a photographer needs to separate keepers from discards simply does not exist in the app. You can mark a photo as a favourite, but a binary favourite is not a rating. It cannot tell you which of three near-identical frames in a burst is the one worth editing.

No culling interface. Even if ratings existed, there is no fast review mode. The web UI presents images one at a time, loaded from the server, in a layout designed for casual browsing. There is no full-screen gesture-driven pass where you swipe right to keep and left to reject, and the app advances automatically to the next frame. The mobile app is slightly more fluid, but it still lacks any concept of a culling session: a dedicated mode where your only job is to decide on each frame, quickly, with ratings written as you go. You are browsing, not culling, and the difference is half an hour of your evening.

No metadata portability. Synology Photos stores everything inside its own database on the NAS. Your album structure, your favourites, your face tags, all of it lives inside the Synology Photos ecosystem. None of it is written to XMP sidecars. None of it travels to Lightroom, Capture One, or Darktable. If you rate photos in another tool, Synology Photos will not see those ratings. If you organise inside Synology Photos, your desktop editor will not know about it. The metadata is walled inside the app.

These are not bugs. They are design decisions for a consumer photo manager. But for a photographer who needs to move metadata between tools, they make Synology Photos a dead end.

CullKit is an independent product. It is not affiliated with or endorsed by Synology Inc. It connects to Synology NAS devices via the standard SMB protocol and the Synology Photos API. Compatibility claims only.

How does CullKit handle culling on a Synology NAS?

CullKit is a dedicated culling and rating app. It is not a photo manager. It does not do face recognition, it does not build timelines, and it does not edit images. Its single job is to help you triage a large folder of photos quickly, and to write every decision you make into a format your editor can read.

When you point CullKit at a folder on your Synology NAS, it opens that folder in a full-screen culling interface. On iPhone and iPad, swipe right to keep a frame and swipe left to reject it. Tap a star to assign a 1-to-5 rating. Apply colour labels from the Lightroom palette, or add text tags for search later. The quick-access bar below each frame gives you all four rating dimensions in a single tap zone. Auto-advance moves you to the next frame immediately after you decide. On Mac, the same workflow runs from the keyboard: number keys for star ratings, P to pick, X to reject, 0 to clear, arrows to navigate. You move through frames at two to three seconds each, the same speed as keyboard culling in Lightroom, but you are doing it directly on the NAS with no import step.

A culling session runs in three phases: first you define the scope (all frames, unrated only, or a filter by minimum rating or label), then the main rating pass, then a batch review where you confirm your selects before the metadata is written. At session end, CullKit writes every rating, flag, label, and tag to XMP sidecar files stored alongside your RAW images on the NAS.

CullKit vs. Synology Photos: what does each one offer?

The two tools address different parts of a photographer’s workflow, and comparing them feature-for-feature clarifies which belongs where.

Culling workflow

Synology Photos has no culling workflow. There is no keep-or-reject mechanic, no session structure, and no batch review. You scroll through a grid and open images one at a time. CullKit is built entirely around the culling decision. The full-screen interface, gesture and keyboard controls, auto-advance, undo, and crash recovery are all designed for one task: move through frames fast and record your decisions.

Star ratings and metadata

Synology Photos offers no star ratings, no reject flags, no colour labels, and no keyword tags. You have a favourite toggle, and that is it. CullKit delivers five-star ratings, pick and reject flags, five colour labels from the Lightroom palette, and free-text tags. All four travel together in the same XMP sidecar.

Speed and interface

The Synology Photos web UI loads images one at a time in a file-browser layout with server round-trips between frames. The mobile app is faster but still operates as a browsing gallery, not a triage deck. CullKit is a native SwiftUI app that renders full-resolution previews progressively on device. No server round-trips between frames. The interface is stripped to the image and the rating controls, with nothing else on screen.

Platform availability

Synology Photos runs on the web, on iOS, and on Android. It covers every platform that can reach a browser. CullKit is Apple-native: iPhone, iPad, and Mac from a single SwiftUI codebase. There is no Android, Windows, or web version. If your workflow runs on Apple hardware, you get a fast, native experience. If you are on Android or Windows, CullKit is not an option.

Metadata portability

This is the largest functional gap between the two tools. Synology Photos stores ratings and organisation inside its own database. Nothing is written to XMP sidecars. If you ever move your library away from Synology Photos, your metadata stays behind. CullKit writes every rating directly to XMP sidecar files. An XMP sidecar is a small text file (a few kilobytes) that sits alongside your RAW on disk. If your file is DSC_4723.NEF, the sidecar is DSC_4723.NEF.xmp. Lightroom, Capture One, and Darktable all read this format natively. When you finish a culling session and open your working folder in Lightroom, your five-star picks are already marked. No re-import. No export step. Your metadata is portable.

Storage reach

Synology Photos works on Synology NAS devices only. It is the official Synology photo app, and it does not connect to other NAS brands. CullKit connects to Synology in two ways: standard SMB (the same protocol Finder uses) and the Synology Photos API for browsing Personal Space, Shared Space, and Albums. But SMB also means CullKit works with QNAP, TrueNAS, UGREEN, Asustor, and any other NAS that exposes a file share. It also reads local folders on your Mac and external SSDs plugged into your iPad. If your photos live somewhere, CullKit can probably reach them. Synology Photos is tied to the Synology ecosystem.

Privacy

Both tools are local by design. Synology Photos runs on your NAS and no photos are uploaded to a cloud unless you explicitly configure Synology’s cloud sync features. CullKit is also 100% local: it processes every frame on your device, writes ratings to your own storage, and stores credentials in your device Keychain. There is no CullKit server, no account that holds your library, and no path for your photos to leave your network. If you chose a NAS to own your data, both tools respect that choice, though they handle the resulting metadata differently. (For more on CullKit’s privacy model, see the privacy FAQ.)

How do I connect CullKit to my Synology library?

CullKit reaches a Synology NAS through two connection methods, and you choose based on how your library is structured.

SMB file share. This is the standard network file-sharing protocol. If your RAWs live in a shared folder on the NAS (for example the default photo share, or a custom shoots share), point CullKit at smb://diskstation.local/photo with your DSM username and password. This method browses the raw folder structure on disk. It is the most direct path, and it is the connection to use for working RAW folders that do not need the Synology Photos album layer.

Synology Photos API. If your library is already organised inside Synology Photos, with albums and shared spaces and the full Synology Photos database, connect via the Photos API. CullKit reads your Personal Space, Shared Space, and Albums directly, preserving the organisation you have already built. You can connect with your QuickConnect ID for remote access, or via local IP for the fastest home-network speed.

Both connection methods produce the same outcome: a full-screen culling session with ratings written as XMP sidecars. The choice is about whether you think in folders or in albums.

Connecting CullKit is a one-time setup. Your credentials are stored securely in the device Keychain, and subsequent sessions open your library directly.

How do my CullKit ratings get into Lightroom?

After you finish a culling session, the ratings you assigned are already on disk alongside your RAW files as XMP sidecars. When you open your desktop editor, they are available immediately.

If the folder is new to your catalogue, import it. Lightroom reads the sidecars during import and applies the ratings. If the folder is already in your catalogue and you culled it afterwards, select the folder in the Library module and run Metadata → Read Metadata from Files. Lightroom pulls in the new star ratings, reject flags, and colour labels in one pass.

RAW and JPEG pairs from the same shot share a single sidecar, following the Lightroom convention. If a frame already had XMP data from a previous tool like Photo Mechanic, CullKit downloads the existing sidecar, merges its own ratings in, and writes the combined file back. Nothing is overwritten.

The handoff from CullKit to your editor is not a sync, not an export, and not a plugin. It is a file sitting in the same folder as your RAW, written in a format your editor was already designed to read.

Does CullKit replace Synology Photos, or work alongside it?

CullKit does not replace Synology Photos. It adds the one layer Synology Photos never shipped: fast, metadata-portable culling.

A photographer who uses both tools might run Synology Photos as their library hub, browsing by face or date, sharing albums with clients, using the mobile app to check a specific frame on location. When a new shoot lands on the NAS, they switch to CullKit for the culling pass, rating the keepers and rejecting the discards in a dedicated session. The ratings live on the NAS as XMP sidecars, ready for Lightroom. Synology Photos remains the library browser. CullKit handles the triage.

They are complementary, and the overlap is small. Synology Photos is where you look at your library. CullKit is where you decide what in your library is worth keeping.

Troubleshooting

CullKit cannot find my NAS. If you are using a local IP address and it stopped working, your DHCP lease probably changed. Assign a static IP to the NAS, or use diskstation.local (Bonjour) for a name-based connection that survives IP changes. Confirm SMB is enabled in DSM under Control Panel → File Services → SMB.

Credentials are rejected. Check that your DSM user account has read-write permissions on the photo share you are trying to connect to (Control Panel → Shared Folder → Edit → Permissions). If your account uses two-step verification, you may need to generate an app password in DSM specifically for CullKit.

Ratings are not appearing in Lightroom. The most common cause is an unfinished culling session: CullKit writes sidecars when the session completes. If you closed the session early, return to it and finish it. If the session completed, run Metadata → Read Metadata from Files on the folder in Lightroom’s Library module.

The culling session feels slow over Wi-Fi. Full-resolution RAW previews stream over the network and render progressively. A 5GHz Wi-Fi connection or a wired NAS makes a noticeable difference with large RAW files. If you are on 2.4GHz and working with 45-megapixel RAWs, expect some render delay between frames.

QuickConnect is slower than the local IP. QuickConnect routes traffic through Synology’s relay servers when a direct connection is not available. On your home network, use the local IP or diskstation.local for maximum speed.

Add culling to your Synology workflow

Synology Photos keeps your library organised. CullKit turns it into a working photographer’s library by adding the culling, rating, and metadata layer that makes every shoot move faster. You keep your NAS. You keep your folder structure. You add a step that removes the slowest part of your post-shoot routine.

CullKit is available on the App Store for iPhone, iPad, and Mac. The free tier lets you browse any connected library: Synology Photos, SMB NAS shares, external SSDs, and local folders. The Pro tier (7-day free trial, then monthly or yearly) unlocks the full culling workflow: star ratings, reject flags, colour labels, XMP sidecar writing, and folder organisation.

A built-in demo mode with seeded sample data lets you experience the full swipe-based culling flow before connecting your own library or committing to the trial.

Download CullKit on the App Store

CullKit is an independent product. It is not affiliated with or endorsed by Synology Inc. It connects to Synology NAS devices via the standard SMB protocol and the Synology Photos API. Compatibility claims only. Synology and Synology Photos are trademarks of Synology Inc.

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