Asynchronous messaging API supporting core pub-sub, request-reply, queue groups, and JetStream persistent messaging with streams, consumers, key-value stores, and object stores.
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asyncapi: 3.0.0
info:
title: NATS Messaging API
version: 2.10.0
description: >-
AsyncAPI specification for NATS messaging patterns including
core pub/sub, request-reply, queue groups, and JetStream
persistent messaging. NATS provides a simple, high-performance
messaging system for cloud-native applications, microservices,
IoT, and edge computing.
contact:
name: NATS.io
url: https://nats.io
license:
name: Apache 2.0
url: https://www.apache.org/licenses/LICENSE-2.0
externalDocs:
description: NATS Documentation
url: https://docs.nats.io
servers:
default:
host: localhost:4222
protocol: nats
description: Default NATS server connection
cluster:
host: localhost:6222
protocol: nats
description: NATS cluster route connection
websocket:
host: localhost:443
protocol: ws
description: NATS WebSocket connection
defaultContentType: application/json
channels:
corePublish:
address: '{subject}'
title: Core NATS Publish
description: >-
Core NATS publish/subscribe channel. Messages are delivered
at-most-once with no persistence. Supports subject-based
routing with wildcards (* for single token, > for multiple tokens).
parameters:
subject:
description: >-
NATS subject for message routing. Supports dot-separated
hierarchical subjects and wildcards. Examples: orders.new,
events.*, logs.>
messages:
coreMessage:
$ref: '#/components/messages/CoreNATSMessage'
requestReply:
address: '{subject}'
title: Request-Reply
description: >-
NATS request-reply pattern. A client sends a request on a
subject and receives a reply on an auto-generated inbox subject.
Supports scatter-gather patterns when multiple responders exist.
parameters:
subject:
description: NATS subject for the request
messages:
request:
$ref: '#/components/messages/RequestMessage'
reply:
$ref: '#/components/messages/ReplyMessage'
queueGroup:
address: '{subject}'
title: Queue Group Subscription
description: >-
Queue group subscriptions distribute messages among members
of a named group. Only one member of the group receives
each message, enabling load-balanced message processing.
parameters:
subject:
description: NATS subject for queue group subscription
messages:
queueMessage:
$ref: '#/components/messages/CoreNATSMessage'
jetStreamPublish:
address: '{stream_subject}'
title: JetStream Publish
description: >-
JetStream publish channel for persistent messaging. Messages
are stored in streams with configurable retention policies,
storage backends, and replication factors. Publishers receive
acknowledgments confirming message storage.
parameters:
stream_subject:
description: >-
JetStream stream subject. Must match a configured stream
subject filter. Example: orders.>, events.processed
messages:
jetStreamMessage:
$ref: '#/components/messages/JetStreamMessage'
publishAck:
$ref: '#/components/messages/JetStreamPublishAck'
jetStreamConsume:
address: '$JS.API.CONSUMER.MSG.NEXT.{stream}.{consumer}'
title: JetStream Consumer
description: >-
JetStream consumer channel for pulling messages from streams.
Consumers track delivery state and support multiple delivery
policies including all, last, new, by-start-sequence, and
by-start-time. Messages require explicit acknowledgment.
parameters:
stream:
description: JetStream stream name
consumer:
description: JetStream consumer name
messages:
consumeMessage:
$ref: '#/components/messages/JetStreamMessage'
jetStreamKeyValue:
address: '$KV.{bucket}.{key}'
title: JetStream Key-Value Store
description: >-
JetStream Key-Value store built on top of streams. Provides
a familiar key-value interface with watch capabilities for
real-time change notification. Supports TTL, history, and
cross-cluster replication.
parameters:
bucket:
description: Key-Value bucket name
key:
description: Key within the bucket
messages:
kvEntry:
$ref: '#/components/messages/KeyValueEntry'
jetStreamObjectStore:
address: '$OBJ.{bucket}'
title: JetStream Object Store
description: >-
JetStream Object Store for storing large objects that exceed
the maximum message size. Objects are chunked and stored in
a stream with metadata tracking.
parameters:
bucket:
description: Object Store bucket name
messages:
objectMeta:
$ref: '#/components/messages/ObjectStoreMeta'
operations:
publishMessage:
action: send
channel:
$ref: '#/channels/corePublish'
summary: Publish a message to a NATS subject
description: >-
Publishes a message to the specified subject. All subscribers
matching the subject receive the message. Fire-and-forget
with at-most-once delivery semantics.
messages:
- $ref: '#/channels/corePublish/messages/coreMessage'
subscribeMessage:
action: receive
channel:
$ref: '#/channels/corePublish'
summary: Subscribe to messages on a NATS subject
description: >-
Subscribes to messages matching the specified subject pattern.
Supports wildcard subjects for flexible routing.
messages:
- $ref: '#/channels/corePublish/messages/coreMessage'
sendRequest:
action: send
channel:
$ref: '#/channels/requestReply'
summary: Send a request and await a reply
description: >-
Sends a request message and waits for a reply on an
auto-generated inbox subject. Supports timeouts.
messages:
- $ref: '#/channels/requestReply/messages/request'
receiveReply:
action: receive
channel:
$ref: '#/channels/requestReply'
summary: Receive a reply to a request
messages:
- $ref: '#/channels/requestReply/messages/reply'
queueSubscribe:
action: receive
channel:
$ref: '#/channels/queueGroup'
summary: Subscribe as part of a queue group
description: >-
Subscribes to messages as a member of a named queue group.
Messages are load-balanced across group members.
messages:
- $ref: '#/channels/queueGroup/messages/queueMessage'
jetStreamPublish:
action: send
channel:
$ref: '#/channels/jetStreamPublish'
summary: Publish a persistent message to a JetStream stream
description: >-
Publishes a message to a JetStream stream. The server
acknowledges successful storage. Supports deduplication
via Nats-Msg-Id header.
messages:
- $ref: '#/channels/jetStreamPublish/messages/jetStreamMessage'
jetStreamConsume:
action: receive
channel:
$ref: '#/channels/jetStreamConsume'
summary: Consume messages from a JetStream consumer
description: >-
Pulls or pushes messages from a JetStream consumer. Requires
explicit acknowledgment (ack, nak, in-progress, term).
messages:
- $ref: '#/channels/jetStreamConsume/messages/consumeMessage'
watchKeyValue:
action: receive
channel:
$ref: '#/channels/jetStreamKeyValue'
summary: Watch for key-value changes
description: >-
Watches a key or wildcard pattern in a Key-Value bucket
for real-time change notifications.
messages:
- $ref: '#/channels/jetStreamKeyValue/messages/kvEntry'
components:
messages:
CoreNATSMessage:
name: CoreNATSMessage
title: Core NATS Message
summary: A basic NATS message with subject, payload, and optional headers
contentType: application/octet-stream
headers:
type: object
properties:
Nats-Msg-Id:
type: string
description: Optional message deduplication ID
payload:
type: object
description: >-
Message payload. NATS is payload-agnostic and supports
any binary or text content.
RequestMessage:
name: RequestMessage
title: NATS Request Message
summary: A request message with an auto-generated reply subject
contentType: application/json
headers:
type: object
properties:
Nats-Msg-Id:
type: string
description: Optional message deduplication ID
payload:
type: object
description: Request payload
ReplyMessage:
name: ReplyMessage
title: NATS Reply Message
summary: A reply message sent in response to a request
contentType: application/json
payload:
type: object
description: Reply payload
JetStreamMessage:
name: JetStreamMessage
title: JetStream Message
summary: >-
A persistent message stored in a JetStream stream with
delivery tracking and acknowledgment support
contentType: application/json
headers:
type: object
properties:
Nats-Msg-Id:
type: string
description: Message deduplication ID
Nats-Expected-Stream:
type: string
description: Expected stream name for publish verification
Nats-Expected-Last-Msg-Id:
type: string
description: Expected last message ID for optimistic concurrency
Nats-Expected-Last-Sequence:
type: string
description: Expected last sequence for optimistic concurrency
Nats-Expected-Last-Subject-Sequence:
type: string
description: Expected last subject sequence
payload:
type: object
description: Message payload stored in the stream
JetStreamPublishAck:
name: JetStreamPublishAck
title: JetStream Publish Acknowledgment
summary: Acknowledgment returned after a successful JetStream publish
contentType: application/json
payload:
type: object
properties:
stream:
type: string
description: Name of the stream the message was stored in
seq:
type: integer
description: Sequence number assigned to the message
duplicate:
type: boolean
description: Whether the message was a duplicate
domain:
type: string
description: JetStream domain
KeyValueEntry:
name: KeyValueEntry
title: Key-Value Entry
summary: A key-value entry with revision tracking
contentType: application/json
payload:
type: object
properties:
key:
type: string
description: Entry key
value:
type: string
description: Entry value (base64 encoded if binary)
revision:
type: integer
description: Entry revision number
created:
type: string
format: date-time
description: Entry creation timestamp
operation:
type: string
enum:
- PUT
- DEL
- PURGE
description: Operation type
bucket:
type: string
description: Bucket name
ObjectStoreMeta:
name: ObjectStoreMeta
title: Object Store Metadata
summary: Metadata for an object stored in the Object Store
contentType: application/json
payload:
type: object
properties:
name:
type: string
description: Object name
description:
type: string
description: Object description
size:
type: integer
description: Object size in bytes
chunks:
type: integer
description: Number of chunks
bucket:
type: string
description: Bucket name
nuid:
type: string
description: Unique object identifier
digest:
type: string
description: Object digest for integrity verification
deleted:
type: boolean
description: Whether the object has been deleted