Guides

Choosing a Shopify inventory sync app

Every app in this category claims real-time sync. Here are the seven questions that actually separate them, and the answers that should worry you.

Every app in this category says the same three things: real-time, reliable, easy setup. None of that separates them, and none of it is what goes wrong. What goes wrong is specific, and it is usually invisible until it has cost you an order.

These are the questions worth asking before you install anything — including this one.

1. One-way or two-way?

One-way means one store is the source of truth and the others follow it. Two-way means either store can write, which needs a rule for what happens when both change at once — and every such rule is wrong in some scenario.

Pick one-way unless each store genuinely holds its own separate physical stock. It removes the question instead of answering it. The cost is real and worth naming: edits made in a destination store get overwritten, so everyone has to know which admin owns the number.

2. What happens to a SKU that does not match?

This is the question that predicts the most damage, and it has three possible answers.

• Reported and skipped. The item does not sync, you get told, nothing is corrupted. This is the right answer.
• A new product is created. This is how catalogues get duplicated, and it is one of the most common complaints across every app in this category. Reasonable as a feature you asked for; a catastrophe as a default.
• Guessed at. The worst, because it is silent. If the same SKU appears twice in one store, there is no correct answer to which one the other store should follow — an app that picks will be wrong about half the time and will not tell you.

Ask specifically about the duplicate case, not just the missing case.

3. Can you watch it before it writes?

A dry run against your real catalogue, logging what it would do while touching nothing. Not a demo, not a test store — test stores have clean SKUs, which is precisely what makes them worthless for this. The whole risk lives in the messy parts of your actual data.

If a tool cannot show you its intentions before acting on them, you are trusting a stranger with the number your customers buy against.

4. What happens when you disconnect?

Ask this in writing, and read the one-star reviews for the word “deleted”. This one has its own guide, built on the nineteen reviews in our dataset that mention leaving an app — ten of which are one star.

Some apps remove products they created or reset quantities when a connection is broken. That turns an ordinary migration — the thing you will eventually do — into an incident. The safe answer is that disconnecting stops the sync and changes nothing else, in either store.

5. Is every write logged?

When a number is wrong, the first question is whether the app wrote it. Without a per-write record you cannot answer that, and you end up debugging your own business by guesswork.

A useful log says what was attempted, what happened, and why something was skipped — not just a green tick and a timestamp.

6. How is it priced?

Three axes, and they fail very differently:

Per-variant pricing on a large catalogue is where the bill catches people out, because it moves for reasons unrelated to how much syncing you are doing.

7. Who answers when it breaks?

Inventory sync fails silently by nature — a dropped webhook, an expired token, a catalogue change that quietly stops matching. You will need to ask someone about it eventually, and the useful signal is not response-time promises but whether recent reviews mention support by name or with specifics.

What about speed?

Worth less than any of the above, and usually the only thing the marketing page talks about.

Speed matters in one narrow way: a scheduled sync’s interval is its window of wrongness, and that window gets worse exactly when you are busiest, because more sales land inside it. Event-driven sync does not degrade under load. But an event-driven sync that reads a quantity, does arithmetic, and writes it back can still lose a race against a simultaneous sale — so the question underneath “how fast” is whether the write is conditional. That detail is invisible from outside and worth asking about directly.

A shortlist you can actually run

1. Export products from both stores and count duplicate and blank SKUs. Twenty minutes, and it predicts most of how any app will behave for you.
2. Install the shortlist on the free tier and run each one’s match report against the real catalogue.
3. Compare what they claim matched. Disagreements between two apps on the same data are the most informative thing you will see.
4. Ask each vendor the disconnect question in writing.
5. Only then look at price.

Where StockUnison sits

One-way only. Duplicates reported and never synced. No product ever created in a connected store, nothing ever deleted. Every connection starts in preview mode, every write is logged with its result, and pricing is per live connected store — a destination in preview mode or paused does not count. Support reaches the person who writes the code.

It is the wrong choice if you need two-way sync, marketplace channels, or products and prices copied rather than quantities. And it is new: launched August 2026, with no review history to check, which is a real disadvantage against every established option and one you should weigh rather than take on faith. The free plan exists partly so you can run steps 1 to 3 above without trusting anything.

For the specific apps in this category and their public review records, see the comparison of Syncio and its alternatives. For pricing on this one, see the pricing page.