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X12 Envelope Reference: ISA, GS, ST, SE, GE and IEA Elements

Most X12 file errors that stop a whole interchange happen in the envelope, not in the PO or invoice data. This table lists each element of ISA, GS, ST, SE, GE and IEA with its type and length so you can check a file or build a map.

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Segment	Element	Name	Type	Length (min/max)	Notes
ISA	ISA01	Authorization Information Qualifier	ID	2/2	00 means no authorization information present. Most partners use 00.
ISA	ISA02	Authorization Information	AN	10/10	Ten spaces when ISA01 is 00.
ISA	ISA03	Security Information Qualifier	ID	2/2	00 means no security information present.
ISA	ISA04	Security Information	AN	10/10	Ten spaces when ISA03 is 00.
ISA	ISA05	Interchange ID Qualifier (sender)	ID	2/2	Common values: 01 (DUNS), 12 (phone), 14 (DUNS plus suffix), ZZ (mutually defined).
ISA	ISA06	Interchange Sender ID	AN	15/15	Pad with trailing spaces to exactly 15 characters.
ISA	ISA07	Interchange ID Qualifier (receiver)	ID	2/2	Same code list as ISA05.
ISA	ISA08	Interchange Receiver ID	AN	15/15	Pad with trailing spaces to exactly 15 characters.
ISA	ISA09	Interchange Date	DT	6/6	YYMMDD.
ISA	ISA10	Interchange Time	TM	4/4	HHMM.
ISA	ISA11	Repetition Separator (4020 and later) or Standards ID	ID	1/1	In version 004010 and earlier this is a standards identifier, normally U. From 004020 it holds the repetition separator.
ISA	ISA12	Interchange Control Version Number	ID	5/5	For example 00401 or 00501. Note: this is the envelope version, not the GS08 transaction version.
ISA	ISA13	Interchange Control Number	N0	9/9	Zero padded, unique per interchange, must equal IEA02.
ISA	ISA14	Acknowledgment Requested	ID	1/1	0 no, 1 yes. 1 requests a TA1 interchange acknowledgment.
ISA	ISA15	Interchange Usage Indicator	ID	1/1	P production, T test. Wrong value is a common go-live error.
ISA	ISA16	Component Element Separator	AN	1/1	Often > or :. This character ends the ISA and also tells the parser the sub-element separator.
GS	GS01	Functional Identifier Code	ID	2/2	PO for 850/860, SH for 856, IN for 810, FA for 997, PR for 855, SM for 204.
GS	GS02	Application Sender's Code	AN	2/15	Often matches ISA06 trimmed, but partners may assign a separate code.
GS	GS03	Application Receiver's Code	AN	2/15	Often matches ISA08 trimmed.
GS	GS04	Date	DT	8/8	CCYYMMDD.
GS	GS05	Time	TM	4/8	HHMM, HHMMSS or HHMMSSDD.
GS	GS06	Group Control Number	N0	1/9	Must equal GE02. Unique per group within the interchange.
GS	GS07	Responsible Agency Code	ID	1/2	X for ASC X12.
GS	GS08	Version / Release / Industry Identifier Code	AN	1/12	For example 004010 or 004010VICS or 005010.
ST	ST01	Transaction Set Identifier Code	ID	3/3	For example 850, 855, 856, 810, 997.
ST	ST02	Transaction Set Control Number	AN	4/9	Must equal SE02. Usually starts at 0001 in each group.
ST	ST03	Implementation Convention Reference	AN	1/35	Used in 005010 guides. Absent in most 004010 files.
SE	SE01	Number of Included Segments	N0	1/10	Counts every segment from ST through SE inclusive. A wrong count causes AK502 code 4.
SE	SE02	Transaction Set Control Number	AN	4/9	Must match ST02.
GE	GE01	Number of Transaction Sets Included	N0	1/6	Count of ST/SE pairs in this group.
GE	GE02	Group Control Number	N0	1/9	Must match GS06.
IEA	IEA01	Number of Included Functional Groups	N0	1/5	Count of GS/GE pairs in the interchange.
IEA	IEA02	Interchange Control Number	N0	9/9	Must match ISA13.

The ISA segment is fixed length: 106 characters including the segment terminator. Separators are declared by position inside the ISA (element separator is character 4, component separator is ISA16, segment terminator follows ISA16). Always confirm separators, qualifiers and version with the partner guide.

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How the envelope nests

An interchange starts with ISA and ends with IEA. Inside it are one or more functional groups (GS to GE), and inside each group are transaction sets (ST to SE). Control numbers must match at each level: ISA13 with IEA02, GS06 with GE02, ST02 with SE02. The counts must also match: IEA01 counts groups, GE01 counts sets, and SE01 counts segments in the set.

Fixed length rules in the ISA

The ISA is the only segment where every element has a fixed length, which is how a parser finds the separators before it knows them. That is why ISA06 and ISA08 must be padded to exactly 15 characters and why ISA02 and ISA04 are ten spaces. A sender ID of 9 characters followed by only 3 spaces gives a short ISA, and the partner's gateway will either reject the file or misread the date.

ISA06 and ISA08: exactly 15 characters.
ISA13: exactly 9 digits, zero padded.
ISA15: P for production, T for test.
ISA16: a single character separator, not blank.

Common envelope mistakes

Test files sent with ISA15 set to P cause real orders at the partner. Production files left with T are ignored. Another frequent issue is recycling ISA13 after a counter reset, which gets the interchange dropped as a duplicate. Counters should be stored in the translator and never reset by hand during a live relationship. Check that SE01 counts include the added segments that a mapping tool inserts after the template was designed.

Frequently Asked Questions

Why must ISA06 and ISA08 be 15 characters?

The ISA is a fixed length segment so a parser can read the separators by position before it knows them. IDs shorter than 15 characters are padded with trailing spaces. Without padding, every later element shifts and the interchange fails.

What is the difference between ISA12 and GS08?

ISA12 is the version of the interchange envelope, such as 00401. GS08 is the version of the transaction sets inside the group, such as 004010 or 004010VICS. They often look similar but control different things.

Can ISA13 repeat?

It should not repeat for the same sender and receiver pair. A repeated interchange control number is commonly treated as a duplicate. Keep the counter in the translator and avoid manual resets.

Does SE01 include the ST segment?

Yes. SE01 counts all segments from ST through SE inclusive. A set with ST, BAK, one PO1 and SE has SE01 of 4.

If envelope settings are scattered across spreadsheets for many partners, Netray can help centralize them and compare them to what your ERP integration layer actually sends.

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