PreallocMethod (FIX tag 591)

charFIX 4.4FIX 5.0 SP2

PreallocMethod (tag 591) is a char field defined in FIX 4.4 and FIX 5.0 SP2. It appears in 10 message types, always optionally. It is an enumerated field with 2 defined values.

At a glance

Tag: 591
Name: PreallocMethod
Datatype: char
Dialects: FIX 4.4 and FIX 5.0 SP2
Messages: 10
Valid values: 2

What the specification says

Indicates the method of preallocation.

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

A real message using tag 591

NewOrderSingle · FIX 4.4

Tag	Field	Wire value	Meaning
8	BeginString	FIX.4.4
9	BodyLength	117
35	MsgType	D	Order – Single
49	SenderCompID	BOARTEAM
56	TargetCompID	COUNTERPARTY
34	MsgSeqNum	2
52	SendingTime	20240101-12:00:00.000
11	ClOrdID	ORD-10042
591	PreallocMethod	0	Pro-rata
54	Side	1	Buy
60	TransactTime	20240101-12:00:00.000
40	OrdType	1	Market
10	CheckSum	003

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	Pro-rata	PRO_RATA
1	Do not pro-rata = discuss first	DO_NOT_PRO_RATA_DISCUSS_FIRST

Where tag 591 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 5.0 SP2	Where in the message
CrossOrderCancelReplaceRequest	t	Optional	Optional	inside the SideCrossOrdModGrp component
ExecutionReport	8	Optional	Optional	directly on the message body
MultilegOrderCancelReplace	AC	Optional	Optional	directly on the message body
NewOrderCross	s	Optional	Optional	inside the SideCrossOrdModGrp component
NewOrderList	E	Optional	Optional	inside the ListOrdGrp component
NewOrderMultileg	AB	Optional	Optional	directly on the message body
NewOrderSingle	D	Optional	Optional	directly on the message body
OrderCancelReplaceRequest	G	Optional	Optional	directly on the message body
TradeCaptureReport	AE	Optional	Optional	inside the TrdCapRptSideGrp component
TradeCaptureReportAck	AR	Optional	Optional	directly on the message body

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 591 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 preallocMethod = message.fields[591]?.raw;// e.g. "0" — Pro-rata// The dictionary also carries the labels:const label = fix.dictionary  .fieldByTag(591)  ?.enumValues?.find((e) => e.value === preallocMethod)  ?.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