> ## Documentation Index
> Fetch the complete documentation index at: https://docs.kraken.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Header & Trailer

> Standard FIX message header and trailer fields required in every FIX message.

Every FIX message must include a standard header and trailer. The header contains essential routing and sequence information, while the trailer provides message integrity verification.

<Tabs>
  <Tab title="FIX Specification">
    <ParamField path="8 - BeginString" type="string" required>
      FIX.4.4. Must be the first field in the message.
    </ParamField>

    <ParamField path="9 - BodyLength" type="integer" required>
      Must be the second field in the message.
    </ParamField>

    <ParamField path="35 - MsgType" type="string" required>
      Must be the third field in the message.
    </ParamField>

    <ParamField path="49 - SenderCompID" type="string" required>
      Provided by Customer during onboarding.
    </ParamField>

    <ParamField path="56 - TargetCompID" type="string" required>
      Provided by Customer during onboarding.
    </ParamField>

    <ParamField path="34 - MsgSeqNum" type="integer" required>
      Message sequence number.
    </ParamField>

    <ParamField path="43 - PossDupFlag" type="boolean">
      Always required for retransmitted messages, whether prompted by the sending system or as the result of a resend request.
    </ParamField>

    <ParamField path="97 - PossResend" type="boolean">
      Required when the message may be duplicate of another message sent under a different sequence number.
    </ParamField>

    <ParamField path="52 - SendingTime" type="string">
      Time of message transmission expressed in UTC. Format: YYYYMMDD-HH:MM:SS.uuu (required).
    </ParamField>

    <ParamField path="122 - OrigSendingTime" type="string">
      Required for message re-sent as a result of a ResendRequest. If data is not available set to same value as SendingTime (52). Format: YYYYMMDD-HH:MM:SS.uuu
    </ParamField>

    <ParamField path="10 - CheckSum" type="string" required>
      Three byte, simple checksum. See the FIX spec for details.
    </ParamField>
  </Tab>
</Tabs>