Debug Realtime with Logger and Log Levels

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This is a copy of a troubleshooting article on Supabase's docs site. It may be missing some details from the original. View the original article.

What are logger and log_level parameters?

The Realtime client provides built-in logging to help you debug connection issues, track messages, and understand what's happening with your real-time connections. Two parameters control logging:

• logger: A custom function to handle log messages
• logLevel: Controls which messages the server logs (info, warn, or error)

By default, logging is disabled. When enabled, you can see:

• Messages sent and received
• Connection events (connect, disconnect, errors)
• Heartbeat status
• Channel subscriptions
• Worker events

How to enable logging in your Realtime client

Basic logging to console

import { createClient } from '@supabase/supabase-js'

const supabase = createClient(SUPABASE_URL, SUPABASE_KEY, {
  realtime: {
    logger: (kind, msg, data) => {
      console.log(`${kind}: ${msg}`, data)
    },
  },
})

With log levels for server-side filtering

const supabase = createClient(SUPABASE_URL, SUPABASE_KEY, {
  realtime: {
    logLevel: 'info', // 'info' | 'warn' | 'error'
    logger: (kind, msg, data) => {
      console.log(`[${kind}] ${msg}`, data)
    },
  },
})

Understanding log messages

The logger receives three parameters: kind, msg, and data.

Log kinds you'll see:

push - Messages sent to the server

push: realtime:chat heartbeat (42) {}
push: realtime:chat phx_join (1) { config: {...} }

receive - Messages received from server

receive: ok realtime:chat phx_reply (1) { response: {...} }
receive: realtime:chat broadcast { event: 'message', payload: {...} }

transport - Connection events

transport: connected to wss://project.supabase.co/realtime/v1
transport: heartbeat timeout. Attempting to re-establish connection
transport: close CloseEvent {...}
transport: leaving duplicate topic "realtime:chat"

error - Error events

error: error in heartbeat callback Error: ...
error: error waiting for auth on connect Error: ...

worker - Web Worker events

worker: starting default worker
worker: starting worker for from /worker.js
worker: worker error message

Common debugging scenarios

Debug why channel won't subscribe:

import { createClient } from '@supabase/supabase-js'

const supabase = createClient(SUPABASE_URL, SUPABASE_KEY, {
  realtime: {
    logger: (kind, msg, data) => {
      console.log(`[${kind}] ${msg}`, data)
    },
  },
})

const channel = supabase
  .channel('debug-channel')
  .on('broadcast', { event: 'test' }, (payload) => {
    console.log('Received:', payload)
  })
  .subscribe((status, err) => {
    console.log('Subscribe status:', status, err)
  })

// Check logs for:
// push: realtime:debug-channel phx_join - subscription attempt
// receive: ok realtime:debug-channel phx_reply - successful subscription
// Or error messages if subscription failed

Debug message delivery issues

const supabase = createClient(SUPABASE_URL, SUPABASE_KEY, {
  realtime: {
    logger: (kind, msg, data) => {
      if (kind === 'push' || kind === 'receive') {
        console.log(`[${kind}] ${msg}`, data)
      }
    },
  },
})

const channel = supabase.channel('chat', { config: { broadcast: { self: true } } })

channel.on('broadcast', { event: 'message' }, (payload) => {
  console.log('Message received:', payload)
})
// Send message after subscribing
channel.subscribe((status, err) => {
  if (status == 'SUBSCRIBED') {
    channel.send({
      type: 'broadcast',
      event: 'message',
      payload: { text: 'Hello' },
    })
  } else {
    console.error({ status, err })
  }
})

// Check logs:
// push: realtime:chat broadcast - message sent
// receive: realtime:chat broadcast - message received (if self: true)