NoLegs (FIX tag 555)

NumInGroupFIX 4.4group counter

NoLegs (tag 555) is a NumInGroup field defined in FIX 4.4. It appears in 50 message types and is required in 2 of them. Its datatype is NumInGroup, which makes it a repeating-group counter: its value is the number of entries that follow, not a quantity in its own right.

At a glance

Tag: 555
Name: NoLegs
Datatype: NumInGroup (int)
Dialects: FIX 4.4
Messages: 50

What the specification says

Number of InstrumentLeg repeating group instances.

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

A real message using tag 555

ExecutionReport · FIX 4.4

Tag	Field	Wire value	Meaning
8	BeginString	FIX.4.4
9	BodyLength	163
35	MsgType	8	Execution Report
49	SenderCompID	BOARTEAM
56	TargetCompID	COUNTERPARTY
34	MsgSeqNum	2
52	SendingTime	20240101-12:00:00.000
37	OrderID	ORD-10042
17	ExecID	EXEC-88117
150	ExecType	0	New
39	OrdStatus	0	New
54	Side	1	Buy
151	LeavesQty	0
14	CumQty	1000000
6	AvgPx	1.09215
555	NoLegs2 entries	2	repeating group
600	LegSymbol	EXAMPLE
600	LegSymbol	EXAMPLE
10	CheckSum	235

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 555 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	Requiredness	Where in the message
Advertisement	7	Optional	inside the InstrmtLegGrp component
AllocationInstruction	J	Optional	inside the InstrmtLegGrp component
AllocationReport	AS	Optional	inside the InstrmtLegGrp component
AssignmentReport	AW	Optional	inside the InstrmtLegGrp component
CollateralAssignment	AY	Optional	inside the InstrmtLegGrp component
CollateralInquiry	BB	Optional	inside the InstrmtLegGrp component
CollateralInquiryAck	BG	Optional	inside the InstrmtLegGrp component
CollateralReport	BA	Optional	inside the InstrmtLegGrp component
CollateralRequest	AX	Optional	inside the InstrmtLegGrp component
CollateralResponse	AZ	Optional	inside the InstrmtLegGrp component
Confirmation	AK	Optional	inside the InstrmtLegGrp component
CrossOrderCancelReplaceRequest	t	Optional	inside the InstrmtLegGrp component
CrossOrderCancelRequest	u	Optional	inside the InstrmtLegGrp component
DerivativeSecurityList	AA	Optional	inside RelSymDerivSecGrp › InstrmtLegGrp
DontKnowTrade	Q	Optional	inside the InstrmtLegGrp component
Email	C	Optional	inside the InstrmtLegGrp component
ExecutionReport	8	Optional	inside the InstrmtLegExecGrp component
IOI	6	Optional	inside the InstrmtLegIOIGrp component
MarketDataIncrementalRefresh	X	Optional	inside MDIncGrp › InstrmtLegGrp
MarketDataRequest	V	Optional	inside InstrmtMDReqGrp › InstrmtLegGrp
MarketDataSnapshotFullRefresh	W	Optional	inside the InstrmtLegGrp component
MassQuote	i	Optional	inside QuotSetGrp › QuotEntryGrp › InstrmtLegGrp
MassQuoteAcknowledgement	b	Optional	inside QuotSetAckGrp › QuotEntryAckGrp › InstrmtLegGrp
MultilegOrderCancelReplace	AC	Required	inside the LegOrdGrp component
NewOrderCross	s	Optional	inside the InstrmtLegGrp component
NewOrderMultileg	AB	Required	inside the LegOrdGrp component
News	B	Optional	inside the InstrmtLegGrp component
PositionMaintenanceReport	AM	Optional	inside the InstrmtLegGrp component
PositionMaintenanceRequest	AL	Optional	inside the InstrmtLegGrp component
PositionReport	AP	Optional	inside the InstrmtLegGrp component
Quote	S	Optional	inside the LegQuotGrp component
QuoteCancel	Z	Optional	inside QuotCxlEntriesGrp › InstrmtLegGrp
QuoteRequest	R	Optional	inside QuotReqGrp › QuotReqLegsGrp
QuoteRequestReject	AG	Optional	inside QuotReqRjctGrp › QuotReqLegsGrp
QuoteResponse	AJ	Optional	inside the LegQuotGrp component
QuoteStatusReport	AI	Optional	inside the LegQuotStatGrp component
QuoteStatusRequest	a	Optional	inside the InstrmtLegGrp component
RFQRequest	AH	Optional	inside RFQReqGrp › InstrmtLegGrp
RequestForPositions	AN	Optional	inside the InstrmtLegGrp component
RequestForPositionsAck	AO	Optional	inside the InstrmtLegGrp component
SecurityDefinition	d	Optional	inside the InstrmtLegGrp component
SecurityDefinitionRequest	c	Optional	inside the InstrmtLegGrp component
SecurityList	y	Optional	inside SecListGrp › InstrmtLegSecListGrp
SecurityListRequest	x	Optional	inside the InstrmtLegGrp component
SecurityStatus	f	Optional	inside the InstrmtLegGrp component
SecurityStatusRequest	e	Optional	inside the InstrmtLegGrp component
TradeCaptureReport	AE	Optional	inside the TrdInstrmtLegGrp component
TradeCaptureReportAck	AR	Optional	inside the TrdInstrmtLegGrp component
TradeCaptureReportRequest	AD	Optional	inside the InstrmtLegGrp component
TradeCaptureReportRequestAck	AQ	Optional	inside the InstrmtLegGrp component

Wire format

The number of entries in the repeating group that follows. The next field on the wire is the group's delimiter tag. @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 555 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);// NoLegs is a group counter, so the entries live on message.groups —// NOT on message.fields. message.fields[555] is undefined.const entries = message.groups[555] ?? [];for (const entry of entries) {  // entry.fields is keyed by tag; entry.groups holds nested groups}

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