MDUpdateAction (FIX tag 279)

charFIX 4.4FIX 4.2

MDUpdateAction (tag 279) is a char field defined in FIX 4.4 and FIX 4.2. It appears in 1 message type and is required in 1 of them. It is an enumerated field with 3 defined values.

At a glance

Tag: 279
Name: MDUpdateAction
Datatype: char
Dialects: FIX 4.4 and FIX 4.2
Messages: 1
Valid values: 3

What the specification says

FIX 4.4

Type of Market Data update action

FIX 4.2

Type of Market Data update action.

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

A real message using tag 279

MarketDataIncrementalRefresh · FIX 4.4

Tag	Field	Wire value	Meaning
8	BeginString	FIX.4.4
9	BodyLength	81
35	MsgType	X	Market Data-Incremental Refresh
49	SenderCompID	BOARTEAM
56	TargetCompID	COUNTERPARTY
34	MsgSeqNum	2
52	SendingTime	20240101-12:00:00.000
268	NoMDEntries2 entries	2	repeating group
279	MDUpdateAction	0	New
279	MDUpdateAction	0	New
10	CheckSum	006

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.

Valid values

A value outside this list is not a parse error — the message still decodes — but validate() reports it as validate/value-not-in-enum.

Value	Meaning	Symbolic name
0	New	NEW / New
1	Change	CHANGE / Change
2	Delete	DELETE / Delete

Where tag 279 appears

Requiredness is a property of the message, not of the field: the same tag can be optional in one message and conditionally required in another.

Message	MsgType	FIX 4.4	FIX 4.2	Where in the message
MarketDataIncrementalRefresh	X	Required	Required	inside the MDIncGrp component

Wire format

A single character. Most char fields are enumerated, so the value is one of a fixed set rather than arbitrary text. @boarteam/fix keeps the value as a string and, for enumerated fields, reports validate/value-not-in-enum when it is not a defined value.

Read tag 279 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 mDUpdateAction = message.fields[279]?.raw;// e.g. "0" — New// The dictionary also carries the labels:const label = fix.dictionary  .fieldByTag(279)  ?.enumValues?.find((e) => e.value === mDUpdateAction)  ?.description;

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