How serial tracking works
A serial number stands for one physical unit. Where stock levels tell you that you hold 40 drills, serial tracking tells you which 40: each one has its own record. That record shows where the unit is, what status it's in, which receipt brought it in, which shipment took it out, and every step in between.
Serials or lots?
Both let you trace stock back to where it came from, but they answer different questions.
| Serial numbers | Lots | |
|---|---|---|
| Identifies | One unit | A batch of identical units |
| Typical goods | Electronics, tools, appliances, anything with a warranty or a unit-level recall | Food, supplements, cosmetics, chemicals — anything with an expiry date |
| You record | One serial per unit | A batch number and dates per receipt |
| Answers | Which unit went to which customer? | Which batch is about to expire, and who received it? |
A product can use either, depending on how you sell it. To set up lots, see Set up lot and expiration tracking.
Two switches turn it on
Serial tracking has an account-wide switch, Enable Serial Number Tracking, and a per-product switch, Track serial numbers for this product. Both must be on before a product's serials are recorded. With the account switch off, no product can track serials, whatever its own setting says. See Turn on serial tracking.
How serials are created
Each serial-tracked product has a Generation Mode:
- Manual — you enter each serial as the units arrive. SKU.io rejects a serial that already exists for that product.
- Auto — SKU.io generates serials from a format such as
{sku}-{seq:6}when units arrive, so you don't type them. You can still type your own; SKU.io generates serials only for the units you leave without one. - None — you type serials by hand, as with Manual.
Whatever the mode, a serial can only exist once per product. If a receipt that created a serial is deleted and you later receive the same serial again, SKU.io brings back the original record, so its history stays in one place.
Where a serial goes
Every movement of stock moves its serials with it:
- Receiving a purchase order, an inbound shipment or an inventory increase creates serials In Stock at the receiving warehouse.
- Shipping an order marks its serials Shipped.
- Transferring stock puts its serials In Transit until the destination receives them.
- Returning stock to a vendor marks its serials Returned.
- A stock take shortfall, an inventory adjustment that decreases stock, or units lost in transit mark serials Scrapped.
- Manufacturing or assembling a product marks the component serials Consumed and creates serials for what you made.
- Quarantining a serial holds it back from sale until you release it.
Undoing the document undoes the serial change too. Deleting or voiding a shipment, a transfer, a vendor return, a stock take, an adjustment, a production run or a customer return's receipt puts its serials back where they were.
The Serial numbers reference lists every status and what it means.
When nobody names a serial
You don't always type the serials that leave. A marketplace reports a shipment, a 3PL ships an order, or you simply leave the serial field blank. In each case, SKU.io picks the serials for you, oldest first: it takes the serials that have been In Stock at that warehouse the longest. The same rule applies to vendor returns, stock take shortfalls, components used in manufacturing and transfers.
When you do name serials, SKU.io uses the ones you named and picks the oldest only for any units left over.
A missing serial never blocks a shipment. If the warehouse has fewer serials in stock than the units shipping, the shipment still goes out. The line shows a Serials missing chip with the number of units that have no serial. That usually means the stock arrived without its serials being recorded. Once the serials are recorded, click Assign serials on the shipment to fill the gap; see Fix a "Serials missing" shipment. Record serials every time you receive stock, so later shipments always have serials to pick.
Checking the serials you name
Outbound Serial Match Mode decides what happens when you name a serial that SKU.io can't ship:
- Require exact match — SKU.io blocks the action and tells you which serial is the problem: it isn't on file, it isn't in stock, or it's at a different warehouse. Use this if your serials must always match the shelf.
- Log and allow mismatch — SKU.io records the mismatch and lets the action go ahead. Use this while you're still loading serials for existing stock, so that a gap in your records doesn't stop orders.
Receiving works the same in both modes: a serial that already exists for the product is always rejected.