lighthouse/book/src/websockets.md

Websocket API

By default, a Lighthouse beacon_node exposes a websocket server on localhost:5053.

The following CLI flags control the websocket server:

• --no-ws: disable the websocket server.
• --ws-port: specify the listen port of the server.
• --ws-address: specify the listen address of the server.

All clients connected to the websocket server will receive the same stream of events, all triggered by the BeaconChain. Each event is a JSON object with the following schema:

{
    "event": "string",
    "data": "object"
}

Events

The following events may be emitted:

Beacon Head Changed

Occurs whenever the canonical head of the beacon chain changes.

{
    "event": "beacon_head_changed",
    "data": {
        "reorg": "boolean",
        "current_head_beacon_block_root": "string",
        "previous_head_beacon_block_root": "string"
    }
}

Beacon Finalization

Occurs whenever the finalized checkpoint of the canonical head changes.

{
    "event": "beacon_finalization",
    "data": {
        "epoch": "number",
        "root": "string"
    }
}

Beacon Block Imported

Occurs whenever the beacon node imports a valid block.

{
    "event": "beacon_block_imported",
    "data": {
        "block": "object"
    }
}

Beacon Block Rejected

Occurs whenever the beacon node rejects a block because it is invalid or an error occurred during validation.

{
    "event": "beacon_block_rejected",
    "data": {
        "reason": "string",
        "block": "object"
    }
}

Beacon Attestation Imported

Occurs whenever the beacon node imports a valid attestation.

{
    "event": "beacon_attestation_imported",
    "data": {
        "attestation": "object"
    }
}

Beacon Attestation Rejected

Occurs whenever the beacon node rejects an attestation because it is invalid or an error occurred during validation.

{
    "event": "beacon_attestation_rejected",
    "data": {
        "reason": "string",
        "attestation": "object"
    }
}