OnBehalfOfSendingTime (FIX tag 370)

UTCTimestampFIX 4.2session envelope

OnBehalfOfSendingTime (tag 370) is an UTCTimestamp field defined in FIX 4.2. It belongs to the session envelope: every FIX 4.2 message carries it, so it identifies the session rather than describing the business event.

At a glance

Tag: 370
Name: OnBehalfOfSendingTime
Datatype: UTCTimestamp (String)
Format: YYYYMMDD-HH:MM:SS[.sss]
Dialects: FIX 4.2
Messages: 46

What the specification says

Used when a message is sent via a "hub" or "service bureau". If A sends to Q (the hub) who then sends to B via a separate FIX session, then when Q sends to B the value of this field should represent the SendingTime on the message A sent to Q. (always expressed in UTC (Universal Time Coordinated, also known as "GMT")

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

A real message using tag 370

OrderSingle · FIX 4.2

Tag	Field	Wire value	Meaning
8	BeginString	FIX.4.2
9	BodyLength	153
35	MsgType	D	Order Single
49	SenderCompID	BOARTEAM
56	TargetCompID	COUNTERPARTY
34	MsgSeqNum	2
52	SendingTime	20240101-12:00:00.000
370	OnBehalfOfSendingTime	20240101-12:00:00.000
11	ClOrdID	ORD-10042
21	HandlInst	1	Automated execution order, private, no Broker intervention
55	Symbol	EUR/USD
54	Side	1	Buy
60	TransactTime	20240101-12:00:00.000
40	OrdType	1	Market
10	CheckSum	089

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 4.2 dictionary and verified at build time: it parses and validates with no issues. Open the decoder to try your own message.

Where tag 370 appears

Session envelope field

Tag 370 appears in every one of the 46 FIX 4.2 message types, because it is part of the standard header or trailer. Listing them all would say nothing useful — it is present on anything you will ever decode.

Wire format

A UTC date and time. The fractional-seconds part is optional, so two timestamps can be equal but not byte-identical. @boarteam/fix keeps the value as a string; format rules are checked by validate(), which reports validate/invalid-value rather than throwing.

Read tag 370 in TypeScript

decode.tsts

import { createFixEngine } from "@boarteam/fix";import { dictionary } from "@boarteam/fix-dict-fix42";const fix = createFixEngine(dictionary);const { message, issues } = fix.parse(raw);const field = message.fields[370];field?.name;   // "OnBehalfOfSendingTime"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-fix42

Try the decoder Source on GitHub