Arbitrum Public WebSocket APIs

asyncapi: '2.6.0'
id: 'urn:com:arbitrum:public-wss'
info:
  title: Arbitrum Public WebSocket APIs
  version: '1.0.0'
  description: >-
    AsyncAPI description of the WebSocket surface that Arbitrum exposes from
    publicly documented endpoints.


    ## Important scope notes (from Arbitrum docs)


    Arbitrum's public RPC endpoints — `arb1.arbitrum.io/rpc`,
    `nova.arbitrum.io/rpc`, and `sepolia-rollup.arbitrum.io/rpc` — **do not
    expose JSON-RPC over WebSockets**. The Arbitrum documentation states
    explicitly: "Arbitrum public RPCs do not provide Websocket support."
    Production teams use Alchemy, QuickNode, Infura, Chainstack, dRPC, Ankr,
    Allnodes, or a self-hosted Nitro node to obtain a WSS JSON-RPC endpoint.


    The *only* WebSocket interface Arbitrum publishes on its own domains is the
    **Nitro Sequencer Feed**, a public, read-only broadcast of ordered
    `BroadcastFeedMessage` envelopes. This document describes:


      1. The Nitro Sequencer Feed channels (`arb1`, `nova`, `sepolia`).
      2. The `eth_subscribe` channels that work against an Arbitrum Nitro
         JSON-RPC WebSocket *when one is available* (self-hosted node or
         third-party provider). These are included so consumers can model the
         message shape with Arbitrum's documented block extensions
         (`l1BlockNumber`, `sendRoot`, `sendCount`, modified `mixHash`,
         fixed `difficulty` / `gasLimit`, custom transaction types).


    ## eth_subscribe support on Arbitrum Nitro


      * `newHeads` — supported. Blocks include the Arbitrum-specific fields
        documented under "RPC methods" (`l1BlockNumber`, `sendRoot`,
        `sendCount`, `extraData == sendRoot`, mixed `mixHash`, fixed
        `difficulty` / `gasLimit`).
      * `logs` — supported.
      * `newPendingTransactions` — Arbitrum has a single centralized Sequencer
        and orders transactions on receipt; there is no public mempool, so the
        practical utility differs from L1 Ethereum. The subscription topic is
        accepted by Nitro for compatibility but does not surface a mempool the
        way Ethereum does.
      * `syncing` — accepted by Nitro for go-ethereum compatibility.


    No `arb_subscribe` family of methods is documented by Offchain Labs at the
    time of writing.
  contact:
    name: API Evangelist
    url: https://apievangelist.com
    email: [email protected]
  license:
    name: Arbitrum docs (CC-BY)
    url: https://docs.arbitrum.io
  tags:
    - name: arbitrum
    - name: nitro
    - name: layer-2
    - name: sequencer-feed
    - name: json-rpc
    - name: websocket

defaultContentType: application/json

servers:
  arb1-feed:
    url: arb1-feed.arbitrum.io/feed
    protocol: wss
    description: >-
      Public Nitro Sequencer broadcast feed for Arbitrum One mainnet
      (chain ID 42161). Read-only stream of ordered `BroadcastFeedMessage`
      envelopes. The `blockNumber` carried inside messages refers to the
      parent-chain (L1) block; L2 block number is computed as
      `genesisBlockNumber + sequenceNumber` (Arbitrum One genesis is
      22207817).
  nova-feed:
    url: nova-feed.arbitrum.io/feed
    protocol: wss
    description: >-
      Public Nitro Sequencer broadcast feed for Arbitrum Nova (chain ID 42170,
      AnyTrust DAC chain).
  sepolia-feed:
    url: sepolia-rollup.arbitrum.io/feed
    protocol: wss
    description: >-
      Public Nitro Sequencer broadcast feed for Arbitrum Sepolia testnet
      (chain ID 421614).
  nitro-rpc-ws:
    url: '{host}'
    protocol: wss
    description: >-
      Generic JSON-RPC WebSocket endpoint exposed by a self-hosted Nitro node
      or a third-party provider (Alchemy, QuickNode, Infura, Chainstack, dRPC,
      Ankr, Allnodes). Arbitrum's own public RPC hosts
      (`arb1.arbitrum.io/rpc`, `nova.arbitrum.io/rpc`,
      `sepolia-rollup.arbitrum.io/rpc`) do not accept WebSocket upgrades.
    variables:
      host:
        description: Provider- or operator-supplied WSS host and path.
        default: arb-mainnet.g.alchemy.com/v2/YOUR_KEY

channels:
  /feed/arb1:
    servers:
      - arb1-feed
    description: >-
      Nitro Sequencer broadcast feed for Arbitrum One. The connection is a
      raw WebSocket; each text frame is a JSON `BroadcastMessage`.
    subscribe:
      operationId: receiveArb1SequencerFeed
      summary: Receive ordered sequencer broadcast messages from Arbitrum One.
      message:
        $ref: '#/components/messages/BroadcastMessage'
  /feed/nova:
    servers:
      - nova-feed
    description: Nitro Sequencer broadcast feed for Arbitrum Nova.
    subscribe:
      operationId: receiveNovaSequencerFeed
      summary: Receive ordered sequencer broadcast messages from Arbitrum Nova.
      message:
        $ref: '#/components/messages/BroadcastMessage'
  /feed/sepolia:
    servers:
      - sepolia-feed
    description: Nitro Sequencer broadcast feed for Arbitrum Sepolia testnet.
    subscribe:
      operationId: receiveSepoliaSequencerFeed
      summary: Receive ordered sequencer broadcast messages from Arbitrum Sepolia.
      message:
        $ref: '#/components/messages/BroadcastMessage'

  eth_subscribe/newHeads:
    servers:
      - nitro-rpc-ws
    description: >-
      `eth_subscribe("newHeads")` on a Nitro JSON-RPC WebSocket. Emits a
      notification for every new L2 head produced by the Sequencer. Blocks
      include Arbitrum-specific fields (`l1BlockNumber`, `sendRoot`,
      `sendCount`, modified `mixHash`, fixed `difficulty` / `gasLimit`).
    publish:
      operationId: subscribeNewHeads
      summary: Open a `newHeads` subscription.
      message:
        $ref: '#/components/messages/JsonRpcSubscribeRequestNewHeads'
    subscribe:
      operationId: receiveNewHeads
      summary: Receive `eth_subscription` notifications for new heads.
      message:
        $ref: '#/components/messages/EthSubscriptionNewHead'

  eth_subscribe/logs:
    servers:
      - nitro-rpc-ws
    description: >-
      `eth_subscribe("logs", {address, topics})` on a Nitro JSON-RPC
      WebSocket. Emits a notification for each log matching the supplied
      address/topics filter.
    publish:
      operationId: subscribeLogs
      summary: Open a `logs` subscription with an address/topics filter.
      message:
        $ref: '#/components/messages/JsonRpcSubscribeRequestLogs'
    subscribe:
      operationId: receiveLogs
      summary: Receive `eth_subscription` notifications for matching logs.
      message:
        $ref: '#/components/messages/EthSubscriptionLog'

  eth_subscribe/newPendingTransactions:
    servers:
      - nitro-rpc-ws
    description: >-
      `eth_subscribe("newPendingTransactions")`. Accepted by Nitro for
      go-ethereum compatibility, but Arbitrum's centralized Sequencer orders
      transactions on receipt — there is no public mempool, so the stream is
      effectively empty / of limited use compared to L1 Ethereum.
    publish:
      operationId: subscribeNewPendingTransactions
      summary: Open a `newPendingTransactions` subscription.
      message:
        $ref: '#/components/messages/JsonRpcSubscribeRequestNewPendingTxs'
    subscribe:
      operationId: receiveNewPendingTransactions
      summary: Receive pending transaction hash notifications.
      message:
        $ref: '#/components/messages/EthSubscriptionPendingTxHash'

  eth_subscribe/syncing:
    servers:
      - nitro-rpc-ws
    description: >-
      `eth_subscribe("syncing")`. Accepted by Nitro for go-ethereum
      compatibility. Notifications reflect the local node's sync status.
    publish:
      operationId: subscribeSyncing
      summary: Open a `syncing` subscription.
      message:
        $ref: '#/components/messages/JsonRpcSubscribeRequestSyncing'
    subscribe:
      operationId: receiveSyncing
      summary: Receive `syncing` status notifications.
      message:
        $ref: '#/components/messages/EthSubscriptionSyncing'

components:
  messages:
    BroadcastMessage:
      name: BroadcastMessage
      title: Nitro Sequencer Broadcast Envelope
      summary: >-
        Top-level envelope emitted by the Nitro Sequencer feed broadcaster.
      contentType: application/json
      payload:
        $ref: '#/components/schemas/BroadcastMessage'

    JsonRpcSubscribeRequestNewHeads:
      name: JsonRpcSubscribeRequestNewHeads
      title: eth_subscribe newHeads request
      contentType: application/json
      payload:
        allOf:
          - $ref: '#/components/schemas/JsonRpcRequest'
          - type: object
            properties:
              method:
                const: eth_subscribe
              params:
                type: array
                minItems: 1
                maxItems: 1
                items:
                  - const: newHeads

    JsonRpcSubscribeRequestLogs:
      name: JsonRpcSubscribeRequestLogs
      title: eth_subscribe logs request
      contentType: application/json
      payload:
        allOf:
          - $ref: '#/components/schemas/JsonRpcRequest'
          - type: object
            properties:
              method:
                const: eth_subscribe
              params:
                type: array
                minItems: 1
                maxItems: 2
                items:
                  - const: logs
                  - $ref: '#/components/schemas/LogsFilter'

    JsonRpcSubscribeRequestNewPendingTxs:
      name: JsonRpcSubscribeRequestNewPendingTxs
      title: eth_subscribe newPendingTransactions request
      contentType: application/json
      payload:
        allOf:
          - $ref: '#/components/schemas/JsonRpcRequest'
          - type: object
            properties:
              method:
                const: eth_subscribe
              params:
                type: array
                minItems: 1
                maxItems: 2
                items:
                  - const: newPendingTransactions
                  - type: boolean
                    description: >-
                      Optional boolean. If true, emit full transaction objects
                      instead of just hashes (provider-dependent).

    JsonRpcSubscribeRequestSyncing:
      name: JsonRpcSubscribeRequestSyncing
      title: eth_subscribe syncing request
      contentType: application/json
      payload:
        allOf:
          - $ref: '#/components/schemas/JsonRpcRequest'
          - type: object
            properties:
              method:
                const: eth_subscribe
              params:
                type: array
                minItems: 1
                maxItems: 1
                items:
                  - const: syncing

    EthSubscriptionNewHead:
      name: EthSubscriptionNewHead
      title: eth_subscription notification — newHeads
      contentType: application/json
      payload:
        allOf:
          - $ref: '#/components/schemas/JsonRpcSubscriptionNotification'
          - type: object
            properties:
              params:
                type: object
                properties:
                  subscription:
                    type: string
                  result:
                    $ref: '#/components/schemas/ArbitrumBlockHeader'

    EthSubscriptionLog:
      name: EthSubscriptionLog
      title: eth_subscription notification — logs
      contentType: application/json
      payload:
        allOf:
          - $ref: '#/components/schemas/JsonRpcSubscriptionNotification'
          - type: object
            properties:
              params:
                type: object
                properties:
                  subscription:
                    type: string
                  result:
                    $ref: '#/components/schemas/Log'

    EthSubscriptionPendingTxHash:
      name: EthSubscriptionPendingTxHash
      title: eth_subscription notification — pending tx hash
      contentType: application/json
      payload:
        allOf:
          - $ref: '#/components/schemas/JsonRpcSubscriptionNotification'
          - type: object
            properties:
              params:
                type: object
                properties:
                  subscription:
                    type: string
                  result:
                    type: string
                    pattern: '^0x[0-9a-fA-F]{64}$'
                    description: 32-byte transaction hash.

    EthSubscriptionSyncing:
      name: EthSubscriptionSyncing
      title: eth_subscription notification — syncing
      contentType: application/json
      payload:
        allOf:
          - $ref: '#/components/schemas/JsonRpcSubscriptionNotification'
          - type: object
            properties:
              params:
                type: object
                properties:
                  subscription:
                    type: string
                  result:
                    oneOf:
                      - type: boolean
                        description: false when not syncing.
                      - type: object
                        properties:
                          syncing:
                            type: boolean
                          status:
                            type: object
                            additionalProperties: true

  schemas:
    JsonRpcRequest:
      type: object
      required:
        - jsonrpc
        - id
        - method
      properties:
        jsonrpc:
          type: string
          const: '2.0'
        id:
          oneOf:
            - type: integer
            - type: string
        method:
          type: string
        params:
          type: array

    JsonRpcSubscribeResponse:
      type: object
      required:
        - jsonrpc
        - id
        - result
      properties:
        jsonrpc:
          type: string
          const: '2.0'
        id:
          oneOf:
            - type: integer
            - type: string
        result:
          type: string
          description: Subscription ID (hex-encoded) returned by the node.

    JsonRpcSubscriptionNotification:
      type: object
      required:
        - jsonrpc
        - method
        - params
      properties:
        jsonrpc:
          type: string
          const: '2.0'
        method:
          type: string
          const: eth_subscription
        params:
          type: object
          required:
            - subscription
            - result
          properties:
            subscription:
              type: string
              description: The subscription ID this notification belongs to.
            result:
              description: Subscription-specific payload.

    LogsFilter:
      type: object
      properties:
        address:
          oneOf:
            - type: string
              pattern: '^0x[0-9a-fA-F]{40}$'
            - type: array
              items:
                type: string
                pattern: '^0x[0-9a-fA-F]{40}$'
        topics:
          type: array
          maxItems: 4
          items:
            oneOf:
              - type: 'null'
              - type: string
                pattern: '^0x[0-9a-fA-F]{64}$'
              - type: array
                items:
                  type: string
                  pattern: '^0x[0-9a-fA-F]{64}$'

    ArbitrumBlockHeader:
      type: object
      description: >-
        Block header as returned by an Arbitrum Nitro node. Extends the
        Ethereum block header with Arbitrum-specific fields documented under
        "RPC methods" in the Arbitrum developer docs.
      properties:
        number:
          type: string
          description: L2 block number (hex).
        hash:
          type: string
          pattern: '^0x[0-9a-fA-F]{64}$'
        parentHash:
          type: string
          pattern: '^0x[0-9a-fA-F]{64}$'
        nonce:
          type: string
        sha3Uncles:
          type: string
        logsBloom:
          type: string
        transactionsRoot:
          type: string
        stateRoot:
          type: string
        receiptsRoot:
          type: string
        miner:
          type: string
        difficulty:
          type: string
          const: '0x1'
          description: Fixed at 0x1 on Arbitrum.
        totalDifficulty:
          type: string
        extraData:
          type: string
          description: >-
            On Arbitrum, `extraData` is equivalent to `sendRoot` — the Merkle
            root of the outbox tree state.
        size:
          type: string
        gasLimit:
          type: string
          const: '0x4000000000000'
          description: Fixed at 0x4000000000000 on Arbitrum.
        gasUsed:
          type: string
        timestamp:
          type: string
        transactions:
          type: array
          items:
            type: string
        uncles:
          type: array
          items:
            type: string
        mixHash:
          type: string
          description: >-
            On Arbitrum, the first 8 bytes mirror `sendCount` and the second
            8 bytes mirror `l1BlockNumber`.
        l1BlockNumber:
          type: string
          description: >-
            Arbitrum-specific. Approximate block number of the first
            non-Arbitrum ancestor chain (Ethereum L1 for Arbitrum One / Nova /
            Sepolia) that occurred before this child-chain block.
        sendRoot:
          type: string
          description: >-
            Arbitrum-specific. Merkle root of the outbox tree state. Equal
            to `extraData`.
        sendCount:
          type: string
          description: >-
            Arbitrum-specific. Number of child-to-parent chain messages since
            Nitro genesis.

    Log:
      type: object
      properties:
        address:
          type: string
        topics:
          type: array
          items:
            type: string
        data:
          type: string
        blockNumber:
          type: string
        transactionHash:
          type: string
        transactionIndex:
          type: string
        blockHash:
          type: string
        logIndex:
          type: string
        removed:
          type: boolean

    BroadcastMessage:
      type: object
      description: >-
        Top-level Sequencer feed envelope (Go: `broadcaster/message.BroadcastMessage`).
        Fields use `omitempty`; the feed is forward-compatible and may add
        fields without breaking clients.
      required:
        - version
      properties:
        version:
          type: integer
          description: Broadcast protocol version.
        messages:
          type: array
          items:
            $ref: '#/components/schemas/BroadcastFeedMessage'
        confirmedSequenceNumberMessage:
          $ref: '#/components/schemas/ConfirmedSequenceNumberMessage'

    BroadcastFeedMessage:
      type: object
      description: >-
        A single ordered Sequencer message.
      properties:
        sequenceNumber:
          type: integer
          description: >-
            Monotonic message index. For Arbitrum One, the L2 block number
            equals `22207817 + sequenceNumber` (genesis offset).
        message:
          $ref: '#/components/schemas/MessageWithMetadata'
        blockHash:
          type: string
          pattern: '^0x[0-9a-fA-F]{64}$'
          description: Optional associated L2 block hash.
        signature:
          type: string
          description: Legacy / nullable signature field.
        signatureV2:
          type: string
          description: >-
            Current signature over (chainId, sequenceNumber, blockHash,
            blockMetadata, message).
        blockMetadata:
          type: string
          description: Optional opaque block-related metadata blob.

    MessageWithMetadata:
      type: object
      description: >-
        Carries the L1IncomingMessage plus delayed-message bookkeeping.
      properties:
        message:
          $ref: '#/components/schemas/L1IncomingMessage'
        delayedMessagesRead:
          type: integer

    L1IncomingMessage:
      type: object
      description: >-
        Inbox-message envelope: a header plus the L2 message bytes
        (decodable with Nitro's `ParseL2Transactions`).
      properties:
        header:
          $ref: '#/components/schemas/L1IncomingMessageHeader'
        l2Msg:
          type: string
          description: Base64- or hex-encoded L2 message bytes.

    L1IncomingMessageHeader:
      type: object
      properties:
        kind:
          type: integer
          description: >-
            Message kind. Maps to Arbitrum transaction types — e.g. 100
            (`ArbitrumDepositTx`, 0x64), 101 (`ArbitrumUnsignedTx`, 0x65),
            102 (`ArbitrumContractTx`, 0x66), 104 (`ArbitrumRetryTx`, 0x68),
            105 (`ArbitrumSubmitRetryableTx`, 0x6A), 106
            (`ArbitrumInternalTx`, 0x6B).
        sender:
          type: string
          pattern: '^0x[0-9a-fA-F]{40}$'
        blockNumber:
          type: integer
          description: >-
            Parent-chain (L1) block number at which this inbox message was
            posted — NOT the L2 block number.
        timestamp:
          type: integer
          description: Parent-chain (L1) timestamp.
        requestId:
          type: string
          description: >-
            Parent-to-child inbox queue position. Surfaces on cross-chain
            transactions.
        baseFeeL1:
          type: string
          description: Parent-chain base fee at the time of inclusion.

    ConfirmedSequenceNumberMessage:
      type: object
      properties:
        sequenceNumber:
          type: integer
          description: Highest sequencer number confirmed at this point in the stream.