AltMDSourceID (FIX tag 817)

StringFIX 4.4

AltMDSourceID (tag 817) is a String field defined in FIX 4.4. It appears in 1 message type, always optionally.

At a glance

Tag: 817
Name: AltMDSourceID
Datatype: String
Dialects: FIX 4.4
Messages: 1

What the specification says

Session layer source for market data (For the standard FIX session layer, this would be the TargetCompID (56) where market data can be obtained).

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

A real message using tag 817

MarketDataRequestReject · FIX 4.4

Tag	Field	Wire value	Meaning
8	BeginString	FIX.4.4
9	BodyLength	103
35	MsgType	Y	Market Data Request Reject
49	SenderCompID	BOARTEAM
56	TargetCompID	COUNTERPARTY
34	MsgSeqNum	2
52	SendingTime	20240101-12:00:00.000
262	MDReqID	REQ-1
816	NoAltMDSource2 entries	2	repeating group
817	AltMDSourceID	EXAMPLE
817	AltMDSourceID	EXAMPLE
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.

Where tag 817 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
MarketDataRequestReject	Y	Conditional	inside the MDRjctGrp 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 817 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[817];field?.name;   // "AltMDSourceID"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