MsgSeqNum (FIX tag 34)

SeqNumFIX 4.4FIX 4.2session envelope

MsgSeqNum (tag 34) is a SeqNum field defined in FIX 4.4 and FIX 4.2. It belongs to the session envelope: every FIX 4.4 message carries it, so it identifies the session rather than describing the business event.

At a glance

Tag: 34
Name: MsgSeqNum
Datatype: SeqNum (int)
Dialects: FIX 4.4 and FIX 4.2
Messages: 93

What the specification says

FIX 4.4

Integer message sequence number

FIX 4.2

Integer message sequence number.

Descriptions are quoted from the FIX Orchestra sources under the Apache 2.0 licence.

A real message using tag 34

MarketDataIncrementalRefresh · FIX 4.4

Tag	Field	Wire value	Meaning
8	BeginString	FIX.4.4
9	BodyLength	75
35	MsgType	X	Market Data-Incremental Refresh
49	SenderCompID	BOARTEAM
56	TargetCompID	COUNTERPARTY
34	MsgSeqNum	2
52	SendingTime	20240101-12:00:00.000
268	NoMDEntries1 entry	1	repeating group
279	MDUpdateAction	0	New
10	CheckSum	248

Edit and decode it yourself

Shown with | separators for readability. On the wire FIX uses SOH (0x01), an invisible control byte — and because BodyLength and CheckSum are computed over the actual bytes, the two forms have different checksums. Both are valid and both decode here.

Open in the full decoder →

Generated from the FIX 4.4 dictionary and verified at build time: it parses and validates with no issues. Open the decoder to try your own message.

Where tag 34 appears

Session envelope field

Tag 34 appears in every one of the 93 FIX 4.4 message types, because it is part of the standard header or trailer. Listing them all would say nothing useful — it is present on anything you will ever decode.

Wire format

A positive sequence number. Session-level, and monotonic within a session. @boarteam/fix parses the value as a number and reports parse/invalid-int when it does not lex as one; the raw string is kept either way.

Read tag 34 in TypeScript

decode.tsts

import { createFixEngine } from "@boarteam/fix";import { dictionary } from "@boarteam/fix-dict-fix44";const fix = createFixEngine(dictionary);const { message, issues } = fix.parse(raw);const field = message.fields[34];field?.name;   // "MsgSeqNum"field?.raw;    // the verbatim wire stringfield?.value;  // coerced to a number

Other SeqNum fields

Decode this in your own code

The same engine that produced the decoded example above is an Apache-2.0 npm package with zero runtime dependencies. It runs in Node and in the browser, and parse() returns problems as data instead of throwing.

npm i @boarteam/fix @boarteam/fix-dict-fix44

Try the decoder Source on GitHub