A purchase order tells you what a retailer wants. An invoice tells them what you want. The 856 sits between the two and tells the receiving dock what is on the truck, before the truck arrives. When it is late, incomplete or wrong, the dock has to count by hand, and someone sends you a bill for the time (here is how to dispute one).
This walkthrough follows a single shipment from the first segment to the last. You can read it with your own 856 open beside it.
The shape: shipment, order, pack, item
Every 856 is a tree. Each level opens with an HL segment, and its third element says which level it is: S for the shipment, O for each purchase order on it, P for each carton or pallet, and I for each item inside a carton. New to X12 itself? Read the X12 file format, explained.
- Shipment: carrier, bill of lading, ship date, ship-to location.
- Order: the PO number this part of the shipment fills.
- Pack: one SSCC-18 label per carton, in a
MAN*GMsegment. - Item: the UPC and how many units are in that carton.
HL*2*1*O~ PRF*4500012345~ HL*3*2*P~ MAN*GM*00012345600000000018~ HL*4*3*I~ LIN**UP*012345678905~ SN1**24*EA~
What the dock checks first
Receiving software does not read your 856 the way you wrote it. It reads it the way a person with a scanner would: carton by carton. When a label is scanned, the system looks for that SSCC in the ASN it already has. If it finds it, it knows what is inside without opening the box.
“If the label on the box and the MAN segment in the file disagree, the file loses. Every time.”
Timing
Most guides require the 856 to arrive before the shipment does, often within a set window after it leaves your dock. Your partner’s guide gives the exact rule; it is usually in the 856 section or the vendor compliance manual. Our retailer EDI requirements pages summarize the deadlines of major retailers.
Quantities
The SN1 quantities across every carton should add up to what physically ships, and should not exceed what the PO ordered unless the partner allows overshipping.
Carrier and bill of lading
The SCAC in TD5 and the reference in REF*BM let the dock match your ASN to the delivery appointment. A missing bill of lading is one of the most common reasons an ASN is rejected outright.
How Weredi handles this
A new 856 starts from the purchase order, so the order and item levels are already filled in. Weredi prints the SSCC-18 carton labels from the same data, so the labels and the MAN segments cannot drift apart.
In short
Send it on time, make the labels and the file agree, and let the quantities add up. Everything else in the 856 exists to make those three things checkable. The carton side is covered in SSCC-18 labels and GS1-128 barcodes, and the fees for getting it wrong in the most common EDI chargebacks.
Questions
What is an EDI 856?
An 856, or advance ship notice (ASN), is the X12 document a supplier sends to tell the retailer what is on a shipment before it arrives: the carrier, the purchase orders it fills, each carton’s SSCC label and the items inside.
When must the 856 be sent?
Before the shipment arrives, usually within a set window after it leaves your dock. The exact rule is in your retailer’s implementation guide.
What happens if the 856 is late or wrong?
The receiving dock has to count by hand, and many retailers charge a fee or take a deduction. The 856 and the partner’s 997 are your evidence if you dispute it: see building a dispute pack.