EncodedUnderlyingSecurityDesc (FIX tag 365)

dataFIX 4.4FIX 4.2FIX 5.0 SP2

EncodedUnderlyingSecurityDesc (tag 365) is a data field defined in FIX 4.4, FIX 4.2 and FIX 5.0 SP2. It appears in 59 message types, always optionally. It is length-prefixed — tag 364 carries the byte count, so the value may contain the SOH separator without breaking the message.

At a glance

Tag: 365
Name: EncodedUnderlyingSecurityDesc
Datatype: data
Dialects: FIX 4.4, FIX 4.2 and FIX 5.0 SP2
Messages: 59
Length field: tag 364

What the specification says

FIX 4.4

Encoded (non-ASCII characters) representation of the UnderlyingSecurityDesc (307) field in the encoded format specified via the MessageEncoding (347) field. If used, the ASCII (English) representation should also be specified in the UnderlyingSecurityDesc field.

FIX 4.2

Encoded (non-ASCII characters) representation of the UnderlyingSecurityDesc field in the encoded format specified via the MessageEncoding field. If used, the ASCII (English) representation should also be specified in the UnderlyingSecurityeDesc field.

FIX 5.0 SP2

Encoded (non-ASCII characters) representation of the UnderlyingSecurityDesc (307) field in the encoded format specified via the MessageEncoding (347) field. If used, the ASCII (English) representation should also be specified in the UnderlyingSecurityeDesc field.

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

A real message using tag 365

NewOrderSingle · FIX 4.4

Tag	Field	Wire value	Meaning
8	BeginString	FIX.4.4
9	BodyLength	177
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
711	NoUnderlyings2 entries	2	repeating group
311	UnderlyingSymbol	EXAMPLE
364	EncodedUnderlyingSecurityDescLen	7
365	EncodedUnderlyingSecurityDesc	EXAMPLE
311	UnderlyingSymbol	EXAMPLE
364	EncodedUnderlyingSecurityDescLen	7
365	EncodedUnderlyingSecurityDesc	EXAMPLE
54	Side	1	Buy
60	TransactTime	20240101-12:00:00.000
40	OrdType	1	Market
10	CheckSum	183

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 365 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	FIX 5.0 SP2	Where in the message
Advertisement	7	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
AllocationInstruction	J	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
AllocationInstructionAlert	BM	—	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
AllocationReport	AS	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
AssignmentReport	AW	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
CollateralAssignment	AY	Conditional	—	Optional	inside UndInstrmtCollGrp › UnderlyingInstrument
CollateralInquiry	BB	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
CollateralInquiryAck	BG	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
CollateralReport	BA	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
CollateralRequest	AX	Conditional	—	Optional	inside UndInstrmtCollGrp › UnderlyingInstrument
CollateralResponse	AZ	Conditional	—	Optional	inside UndInstrmtCollGrp › UnderlyingInstrument
Confirmation	AK	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
ContraryIntentionReport	BO	—	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
CrossOrderCancelReplaceRequest	t	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
CrossOrderCancelRequest	u	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
DerivativeSecurityList	AA	Conditional	—	Optional	inside the UnderlyingInstrument component
DerivativeSecurityListRequest	z	Conditional	—	Optional	inside the UnderlyingInstrument component
DerivativeSecurityListUpdateReport	BR	—	—	Optional	inside the UnderlyingInstrument component
DontKnowTrade	Q	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
Email	C	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
ExecutionAcknowledgement	BN	—	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
ExecutionReport	8	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
IOI	6	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
ListStrikePrice	m	Conditional	—	Optional	inside UndInstrmtStrkPxGrp › UnderlyingInstrument
MarketDataIncrementalRefresh	X	Conditional	—	Optional	inside MDIncGrp › UndInstrmtGrp › UnderlyingInstrument
MarketDataRequest	V	Conditional	—	Optional	inside InstrmtMDReqGrp › UndInstrmtGrp › UnderlyingInstrument
MarketDataSnapshotFullRefresh	W	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
MassQuote	i	Conditional	Optional	Optional	inside QuotSetGrp › UnderlyingInstrument
MassQuoteAcknowledgement	b	Conditional	Optional	Optional	inside QuotSetAckGrp › UnderlyingInstrument
MultilegOrderCancelReplace	AC	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
NewOrderCross	s	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
NewOrderList	E	Conditional	—	Optional	inside ListOrdGrp › UndInstrmtGrp › UnderlyingInstrument
NewOrderMultileg	AB	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
NewOrderSingle	D	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
News	B	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
OrderCancelReplaceRequest	G	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
OrderCancelRequest	F	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
OrderMassActionReport	BZ	—	—	Optional	inside the UnderlyingInstrument component
OrderMassActionRequest	CA	—	—	Optional	inside the UnderlyingInstrument component
OrderMassCancelReport	r	Conditional	—	Optional	inside the UnderlyingInstrument component
OrderMassCancelRequest	q	Conditional	—	Optional	inside the UnderlyingInstrument component
OrderMassStatusRequest	AF	Conditional	—	Optional	inside the UnderlyingInstrument component
OrderStatusRequest	H	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
PositionMaintenanceReport	AM	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
PositionMaintenanceRequest	AL	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
PositionReport	AP	Conditional	—	Optional	inside PosUndInstrmtGrp › UnderlyingInstrument
Quote	S	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
QuoteCancel	Z	Conditional	—	Optional	inside QuotCxlEntriesGrp › UndInstrmtGrp › UnderlyingInstrument
QuoteRequest	R	Conditional	—	Optional	inside QuotReqGrp › UndInstrmtGrp › UnderlyingInstrument
QuoteRequestReject	AG	Conditional	—	Optional	inside QuotReqRjctGrp › UndInstrmtGrp › UnderlyingInstrument
QuoteResponse	AJ	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
QuoteStatusReport	AI	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
QuoteStatusRequest	a	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
RFQRequest	AH	Conditional	—	Optional	inside RFQReqGrp › UndInstrmtGrp › UnderlyingInstrument
RequestForPositions	AN	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
RequestForPositionsAck	AO	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
SecurityDefinition	d	Conditional	Optional	Optional	inside UndInstrmtGrp › UnderlyingInstrument
SecurityDefinitionRequest	c	Conditional	Optional	Optional	inside UndInstrmtGrp › UnderlyingInstrument
SecurityDefinitionUpdateReport	BP	—	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
SecurityList	y	Conditional	—	Optional	inside SecListGrp › UndInstrmtGrp › UnderlyingInstrument
SecurityListRequest	x	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
SecurityListUpdateReport	BK	—	—	Optional	inside SecLstUpdRelSymGrp › UndInstrmtGrp › UnderlyingInstrument
SecurityStatus	f	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
SecurityStatusRequest	e	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
TradeCaptureReport	AE	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
TradeCaptureReportAck	AR	—	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
TradeCaptureReportRequest	AD	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
TradeCaptureReportRequestAck	AQ	Conditional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument

Wire format

Raw bytes, length-prefixed by a partner field. The value may legally contain the SOH separator, which is why the length matters. @boarteam/fix reads the partner length field first and takes exactly that many bytes, so an embedded separator does not truncate the value.

Read tag 365 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);// Length-prefixed: tag 364 carries the byte count, so the// value may contain the SOH separator without breaking the message.const length = message.fields[364]?.value;const encodedUnderlyingSecurityDesc = message.fields[365]?.raw;

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