Headers

Message headers are used in a variety of JetStream contexts, such de-duplication, auto-purging of messages, metadata from republished messages, and more.

Publish

Headers that can be set by a client when a message being published.

Name	Description	Example	Version
Nats-Msg-Id	Client-defined unique identifier for a message that will be used by the server apply de-duplication within the configured Duplicate Window.	9f01ccf0-8c34-4789-8688-231a2538a98b	2.2.0
Nats-Expected-Stream	Used to assert the published message is received by some expected stream.	my-stream	2.2.0
Nats-Expected-Last-Msg-Id	Used to apply optimistic concurrency control at the stream-level. The value is the last expected Nats-Msg-Id and the server will reject a publish if the current ID does not match.	9f01ccf0-8c34-4789-8688-231a2538a98b	2.2.0
Nats-Expected-Last-Sequence	Used to apply optimistic concurrency control at the stream-level. The value is the last expected sequence and the server will reject a publish if the current sequence does not match.	328	2.2.0
Nats-Expected-Last-Subject-Sequence	Used to apply optimistic concurrency control at the subject-level. The value is the last expected sequence and the server will reject a publish if the current sequence does not match for the message's subject.	38	2.3.1
Nats-Rollup	Used to apply a purge of all prior messages in the stream or at the subject-level.	all for stream, sub for subject	2.6.2

RePublish

Headers set messages that are republished.

Name	Description	Example	Version
Nats-Stream	Name of the stream the message was republished from.	Nats-Stream: my-stream	2.8.3
Nats-Subject	The original subject of the message.	events.mouse_clicked	2.8.3
Nats-Time-Stamp	The original timestamp of the message.	2023-08-23T19:53:05.762416Z	2.8.3
Nats-Sequence	The original sequence of the message.	193	2.8.3
Nats-Last-Sequence	The last sequence of the message having the same subject, otherwise zero if this is the first message for the subject.	190	2.8.3

Sources

Headers that are implicitly added to messages sourced from other streams.

Name	Description	Example	Version
Nats-Stream-Source	Specifies the stream a message sourced from, if applicable.	my-stream	2.2.0

Headers-only

Headers added to messages when the consumer is configured to be "headers only" omitting the body.

Name	Description	Example	Version
Nats-Msg-Size	Indicates the message size in bytes.	1024	2.6.2

Mirror

Headers used for internal flow-control messages for a mirror.

Name	Description	Example	Version
Nats-Last-Consumer			2.2.1
Nats-Last-Stream			2.2.1
Nats-Consumer-Stalled			2.4.0
Nats-Response-Type			2.6.4