ISO 8583 is the international standard for financial transaction messaging between cards, terminals, acquirers, and issuers. A message has a Message Type Indicator, one or two bitmaps marking which data elements are present, and the data elements themselves.

What is the bitmap in ISO 8583?

The bitmap is a 64-bit field where each set bit indicates that the corresponding data element is present. If bit 1 of the primary bitmap is set, a secondary bitmap follows, extending coverage to fields 65 through 128.

ISO 8583 Decoder — Parse MTI, Bitmap & Data Elements

About ISO 8583

ISO 8583 is the messaging standard that moves an authorization, reversal, or settlement record between a terminal, an acquirer, a network, and an issuer. Every message opens with a four-character Message Type Indicator describing its version, class, function, and origin, followed by a bitmap that flags which of the 128 possible data elements are present, and then the data elements themselves in order.

Reading the bitmap

The primary bitmap is 64 bits covering fields 1 through 64
If field 1 is set, a secondary bitmap follows, covering fields 65 through 128
Each set bit means that data element is present in the message body

This decoder identifies the MTI, expands both bitmaps, and lists every present field with its standard name. Field value parsing depends on each acquirer's data-element format table, so values are not split here — the focus is structure and which elements are declared.

Frequently asked questions

What is the MTI?

The Message Type Indicator is the four-digit code at the start of the message — for example 0200 is an authorization request and 0210 its response.

Why only the field list, not field values?

Data-element formats vary by network and acquirer specification. The bitmap and field names are universal; reliably splitting values requires the specific format table.

Integrating with an acquirer host?

We build and certify against acquirer and network specifications regularly. See platform integrations →