Alpaca Market Data Streaming (WebSocket)

asyncapi: '2.6.0'
id: 'urn:markets:alpaca:market-data:websocket'
info:
  title: Alpaca Market Data Streaming (WebSocket)
  version: '1.0.0'
  description: |
    AsyncAPI 2.6 description of Alpaca's **real-time market data WebSocket API**.

    Unlike many providers, Alpaca publishes a genuine, documented public
    WebSocket (`wss://`) surface for streaming market data. Clients open a
    WebSocket connection to a feed-specific endpoint, send an `auth` control
    message, then send `subscribe` messages to select channels per symbol (or
    with a `*` wildcard). The server pushes a continuous stream of market data
    messages until the client unsubscribes or disconnects.

    Endpoints (documented at
    https://docs.alpaca.markets/docs/streaming-market-data and
    https://docs.alpaca.markets/docs/real-time-crypto-pricing-data):

    - Stocks: `wss://stream.data.alpaca.markets/v2/{feed}` where `{feed}` is one
      of `iex`, `sip`, `delayed_sip`, or `test`. The `test` feed streams fake
      symbols (for example `FAKEPACA`) 24/7 for development. On the free Basic
      plan the real-time stock feed is `iex`; the full-market `sip` feed
      requires Algo Trader Plus.
    - Crypto: `wss://stream.data.alpaca.markets/v1beta3/crypto/us`. The
      v1beta3 crypto feed distributes data from Alpaca and Kraken and adds an
      `orderbooks` channel (Level 2 book snapshots and updates).
    - Options: `wss://stream.data.alpaca.markets/v1beta1/{feed}`
      (`indicative` or `opra`).
    - Sandbox mirror: `wss://stream.data.sandbox.alpaca.markets/...`.

    Messages are exchanged as JSON arrays of message objects (msgpack is also
    supported). Each message object carries a `T` field identifying its type:
    control messages (`success`, `error`, `subscription`) and data messages
    (`t` trade, `q` quote, `b` minute bar, `d` daily bar, `u` updated bar,
    `s` trading status, `l` LULD, `c` correction, `x` cancel error, and
    `o` crypto orderbook).

    A separate Trading API account/order WebSocket exists at
    `wss://{paper-}api.alpaca.markets/stream` (listen then receive
    `trade_updates`); it is noted in the review but not modeled in this
    document, which focuses on the market-data stream.
  contact:
    name: API Evangelist
    email: kin@apievangelist.com
    url: https://apievangelist.com
  license:
    name: API documentation - Alpaca Terms of Service
    url: https://alpaca.markets/terms
  x-transport-notes:
    transport: WebSocket
    protocol: wss
    direction: bidirectional (client sends control messages, server pushes data)
    mediaType: application/json (msgpack also supported)
    stocksEndpoint: 'wss://stream.data.alpaca.markets/v2/{feed}'
    cryptoEndpoint: 'wss://stream.data.alpaca.markets/v1beta3/crypto/us'
    optionsEndpoint: 'wss://stream.data.alpaca.markets/v1beta1/{feed}'
    sandboxEndpoint: 'wss://stream.data.sandbox.alpaca.markets'
    source: https://docs.alpaca.markets/docs/streaming-market-data
defaultContentType: application/json
servers:
  stocks:
    url: stream.data.alpaca.markets/v2/{feed}
    protocol: wss
    description: |
      Real-time US equities WebSocket. `{feed}` selects the data source:
      `iex` (free Basic), `sip` (full market, Algo Trader Plus),
      `delayed_sip` (15-minute delayed SIP), or `test` (fake symbols, 24/7).
    variables:
      feed:
        enum:
          - iex
          - sip
          - delayed_sip
          - test
        default: iex
        description: The stock data feed.
    security:
      - apiKeyAuth: []
  crypto:
    url: stream.data.alpaca.markets/v1beta3/crypto/us
    protocol: wss
    description: |
      Real-time crypto WebSocket (v1beta3), distributing Alpaca and Kraken
      data. Adds the `orderbooks` channel for Level 2 market depth.
    security:
      - apiKeyAuth: []
channels:
  /v2/{feed}:
    description: |
      Stock market data stream. After connecting, the server sends a
      `[{"T":"success","msg":"connected"}]` control message. The client then
      sends an `auth` message, receives
      `[{"T":"success","msg":"authenticated"}]`, and sends `subscribe`
      messages. The server thereafter pushes arrays of data messages (trades,
      quotes, bars, etc.) for the subscribed symbols.
    parameters:
      feed:
        description: The stock data feed (iex, sip, delayed_sip, test).
        schema:
          type: string
    publish:
      operationId: sendStockControlMessage
      summary: Send a control message (auth, subscribe, unsubscribe).
      description: |
        Client-to-server control frames. The first frame after connecting must
        be `auth`; subsequent frames add or remove channel subscriptions.
      message:
        oneOf:
          - $ref: '#/components/messages/AuthMessage'
          - $ref: '#/components/messages/SubscribeMessage'
          - $ref: '#/components/messages/UnsubscribeMessage'
    subscribe:
      operationId: receiveStockDataMessages
      summary: Receive streamed market data and control acknowledgements.
      description: |
        Server-to-client frames. Each frame is a JSON array of one or more
        message objects; each object's `T` field identifies its type.
      message:
        oneOf:
          - $ref: '#/components/messages/SuccessMessage'
          - $ref: '#/components/messages/ErrorMessage'
          - $ref: '#/components/messages/SubscriptionMessage'
          - $ref: '#/components/messages/TradeMessage'
          - $ref: '#/components/messages/QuoteMessage'
          - $ref: '#/components/messages/BarMessage'
          - $ref: '#/components/messages/TradingStatusMessage'
  /v1beta3/crypto/us:
    description: |
      Crypto market data stream. Same auth/subscribe handshake as the stock
      stream, plus an `orderbooks` channel carrying Level 2 book snapshots
      (first message per symbol) and incremental updates.
    publish:
      operationId: sendCryptoControlMessage
      summary: Send a crypto control message (auth, subscribe, unsubscribe).
      description: Client-to-server control frames for the crypto stream.
      message:
        oneOf:
          - $ref: '#/components/messages/AuthMessage'
          - $ref: '#/components/messages/SubscribeMessage'
          - $ref: '#/components/messages/UnsubscribeMessage'
    subscribe:
      operationId: receiveCryptoDataMessages
      summary: Receive streamed crypto market data.
      description: Server-to-client frames including trades, quotes, bars, and orderbooks.
      message:
        oneOf:
          - $ref: '#/components/messages/SuccessMessage'
          - $ref: '#/components/messages/ErrorMessage'
          - $ref: '#/components/messages/SubscriptionMessage'
          - $ref: '#/components/messages/TradeMessage'
          - $ref: '#/components/messages/QuoteMessage'
          - $ref: '#/components/messages/BarMessage'
          - $ref: '#/components/messages/OrderbookMessage'
components:
  securitySchemes:
    apiKeyAuth:
      type: userPassword
      description: |
        Alpaca API key ID and secret, supplied in the WebSocket `auth`
        control message body as `{"action":"auth","key":"<KEY_ID>","secret":"<SECRET>"}`.
        For OAuth-based apps, send `"key":"oauth"` and `"secret":"<ACCESS_TOKEN>"`.
  messages:
    AuthMessage:
      name: AuthMessage
      title: Authenticate
      summary: First client message; authenticates the connection.
      contentType: application/json
      payload:
        type: object
        required:
          - action
          - key
          - secret
        properties:
          action:
            type: string
            enum:
              - auth
          key:
            type: string
            description: API key ID (or the literal "oauth" for OAuth access tokens).
          secret:
            type: string
            description: API secret key (or the OAuth access token).
      examples:
        - name: auth
          payload:
            action: auth
            key: PK00000000000000000
            secret: aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
    SubscribeMessage:
      name: SubscribeMessage
      title: Subscribe
      summary: Subscribe to one or more channels per symbol or with a wildcard.
      contentType: application/json
      payload:
        type: object
        required:
          - action
        properties:
          action:
            type: string
            enum:
              - subscribe
          trades:
            type: array
            items:
              type: string
            description: Symbols to receive trades for. Use ["*"] for all symbols.
          quotes:
            type: array
            items:
              type: string
            description: Symbols to receive quotes for.
          bars:
            type: array
            items:
              type: string
            description: Symbols to receive minute bars for.
          dailyBars:
            type: array
            items:
              type: string
            description: Symbols to receive daily bars for.
          updatedBars:
            type: array
            items:
              type: string
            description: Symbols to receive updated (late/corrected) bars for.
          statuses:
            type: array
            items:
              type: string
            description: Symbols to receive trading status events for.
          orderbooks:
            type: array
            items:
              type: string
            description: Crypto pairs to receive Level 2 orderbook data for (crypto stream only).
      examples:
        - name: subscribeStocks
          summary: Subscribe to AAPL trades and quotes, all-symbol bars
          payload:
            action: subscribe
            trades:
              - AAPL
            quotes:
              - AAPL
              - TSLA
            bars:
              - '*'
        - name: subscribeCryptoOrderbook
          summary: Subscribe to BTC/USD orderbook
          payload:
            action: subscribe
            orderbooks:
              - BTC/USD
    UnsubscribeMessage:
      name: UnsubscribeMessage
      title: Unsubscribe
      summary: Remove channel subscriptions.
      contentType: application/json
      payload:
        type: object
        required:
          - action
        properties:
          action:
            type: string
            enum:
              - unsubscribe
          trades:
            type: array
            items:
              type: string
          quotes:
            type: array
            items:
              type: string
          bars:
            type: array
            items:
              type: string
    SuccessMessage:
      name: SuccessMessage
      title: Success control frame
      summary: Server acknowledgement (connected / authenticated).
      contentType: application/json
      payload:
        type: object
        properties:
          T:
            type: string
            enum:
              - success
          msg:
            type: string
            description: For example "connected" or "authenticated".
      examples:
        - name: authenticated
          payload:
            T: success
            msg: authenticated
    ErrorMessage:
      name: ErrorMessage
      title: Error control frame
      summary: Server error (bad auth, invalid subscription, connection limit, etc.).
      contentType: application/json
      payload:
        type: object
        properties:
          T:
            type: string
            enum:
              - error
          code:
            type: integer
            description: Alpaca stream error code (for example 402 not authenticated, 406 connection limit exceeded).
          msg:
            type: string
            description: Human-readable error message.
      examples:
        - name: notAuthenticated
          payload:
            T: error
            code: 402
            msg: auth failed
    SubscriptionMessage:
      name: SubscriptionMessage
      title: Subscription control frame
      summary: Server echo of the current active subscriptions after a subscribe/unsubscribe.
      contentType: application/json
      payload:
        type: object
        properties:
          T:
            type: string
            enum:
              - subscription
          trades:
            type: array
            items:
              type: string
          quotes:
            type: array
            items:
              type: string
          bars:
            type: array
            items:
              type: string
      examples:
        - name: current
          payload:
            T: subscription
            trades:
              - AAPL
            quotes:
              - AAPL
              - TSLA
            bars:
              - '*'
    TradeMessage:
      name: TradeMessage
      title: Trade (T=t)
      summary: A single executed trade.
      contentType: application/json
      payload:
        type: object
        properties:
          T:
            type: string
            enum:
              - t
          S:
            type: string
            description: Symbol.
          i:
            type: integer
            description: Trade ID.
          p:
            type: number
            description: Trade price.
          s:
            type: integer
            description: Trade size.
          t:
            type: string
            format: date-time
            description: RFC-3339 timestamp with nanoseconds.
          x:
            type: string
            description: Exchange code.
          c:
            type: array
            items:
              type: string
            description: Trade condition flags.
          z:
            type: string
            description: Tape (A, B, or C) for stocks.
      examples:
        - name: trade
          payload:
            T: t
            S: AAPL
            i: 12345
            p: 195.62
            s: 100
            t: '2026-07-11T14:30:00.123456789Z'
            x: V
            c:
              - '@'
            z: C
    QuoteMessage:
      name: QuoteMessage
      title: Quote (T=q)
      summary: A national best bid/offer (or crypto) quote.
      contentType: application/json
      payload:
        type: object
        properties:
          T:
            type: string
            enum:
              - q
          S:
            type: string
            description: Symbol.
          bp:
            type: number
            description: Bid price.
          bs:
            type: integer
            description: Bid size.
          ap:
            type: number
            description: Ask price.
          as:
            type: integer
            description: Ask size.
          t:
            type: string
            format: date-time
            description: RFC-3339 timestamp.
      examples:
        - name: quote
          payload:
            T: q
            S: AAPL
            bp: 195.6
            bs: 3
            ap: 195.63
            as: 2
            t: '2026-07-11T14:30:00.123456789Z'
    BarMessage:
      name: BarMessage
      title: Bar (T=b/d/u)
      summary: An OHLCV aggregate bar (minute, daily, or updated).
      contentType: application/json
      payload:
        type: object
        properties:
          T:
            type: string
            enum:
              - b
              - d
              - u
            description: b minute bar, d daily bar, u updated bar.
          S:
            type: string
            description: Symbol.
          o:
            type: number
            description: Open price.
          h:
            type: number
            description: High price.
          l:
            type: number
            description: Low price.
          c:
            type: number
            description: Close price.
          v:
            type: integer
            description: Volume.
          t:
            type: string
            format: date-time
            description: Bar timestamp.
      examples:
        - name: minuteBar
          payload:
            T: b
            S: AAPL
            o: 195.5
            h: 195.7
            l: 195.4
            c: 195.62
            v: 12500
            t: '2026-07-11T14:30:00Z'
    TradingStatusMessage:
      name: TradingStatusMessage
      title: Trading status (T=s)
      summary: A trading halt/resume or LULD status change for a symbol.
      contentType: application/json
      payload:
        type: object
        properties:
          T:
            type: string
            enum:
              - s
          S:
            type: string
            description: Symbol.
          sc:
            type: string
            description: Status code.
          sm:
            type: string
            description: Status message.
          t:
            type: string
            format: date-time
            description: Timestamp.
    OrderbookMessage:
      name: OrderbookMessage
      title: Crypto orderbook (T=o)
      summary: A Level 2 orderbook snapshot or update (crypto stream only).
      contentType: application/json
      payload:
        type: object
        properties:
          T:
            type: string
            enum:
              - o
          S:
            type: string
            description: Crypto pair, for example BTC/USD.
          t:
            type: string
            format: date-time
            description: Timestamp.
          b:
            type: array
            description: Bid levels. First message per symbol is a full snapshot; subsequent messages are updates.
            items:
              type: object
              properties:
                p:
                  type: number
                  description: Price level.
                s:
                  type: number
                  description: Size at the level (0 removes the level).
          a:
            type: array
            description: Ask levels.
            items:
              type: object
              properties:
                p:
                  type: number
                  description: Price level.
                s:
                  type: number
                  description: Size at the level (0 removes the level).
          r:
            type: boolean
            description: Reset flag - true when this message is a full snapshot.
      examples:
        - name: orderbookSnapshot
          payload:
            T: o
            S: BTC/USD
            t: '2026-07-11T14:30:00.123456789Z'
            b:
              - p: 61000.5
                s: 0.25
            a:
              - p: 61002.0
                s: 0.4
            r: true