ListID (FIX tag 66)

StringFIX 4.4FIX 4.2

ListID (tag 66) is a String field defined in FIX 4.4 and FIX 4.2. It appears in 17 message types and is required in 6 of them.

At a glance

Tag: 66
Name: ListID
Datatype: String
Dialects: FIX 4.4 and FIX 4.2
Messages: 17

What the specification says

Unique identifier for list as assigned by institution, used to associate multiple individual orders. Uniqueness must be guaranteed within a single trading day. Firms which generate multi-day orders should consider embedding a date within the ListID field to assure uniqueness across days.

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

A real message using tag 66

ExecutionReport · FIX 4.4

Tag	Field	Wire value	Meaning
8	BeginString	FIX.4.4
9	BodyLength	144
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
66	ListID	EXAMPLE
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
10	CheckSum	209

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 66 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
AllocationInstruction	J	Optional	Optional	inside the OrdAllocGrp component
AllocationReport	AS	Optional	—	inside the OrdAllocGrp component
BidRequest	k	Conditional	Optional	inside the BidCompReqGrp component
BidResponse	l	Conditional	Optional	inside the BidCompRspGrp component
Confirmation	AK	Optional	—	inside the OrdAllocGrp component
ConfirmationRequest	BH	Optional	—	inside the OrdAllocGrp component
ExecutionReport	8	Optional	Optional	directly on the message body
ListCancelRequest	K	Required	Required	directly on the message body
ListExecute	L	Required	Required	directly on the message body
ListStatus	N	Required	Required	directly on the message body
ListStatusRequest	M	Required	Required	directly on the message body
ListStrikePrice	m	Required	Required	directly on the message body
NewOrderList	E	Required	Required	directly on the message body
OrderCancelReject	9	Optional	Optional	directly on the message body
OrderCancelReplaceRequest	G	Optional	Optional	directly on the message body
OrderCancelRequest	F	Optional	Optional	directly on the message body
TradeCaptureReport	AE	Optional	—	inside the TrdCapRptSideGrp component

Wire format

Free-form text. Any byte except the SOH separator is legal, so values are not trimmed or case-folded on the wire. @boarteam/fix keeps the value as a string; format rules are checked by validate(), which reports validate/invalid-value rather than throwing.

Read tag 66 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[66];field?.name;   // "ListID"field?.raw;    // the verbatim wire stringfield?.value;  // coerced to a string

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