Next.js

2

Get your project token

Required

You’ll need your PostHog project token to authenticate log requests. This is the same key you use for capturing events and exceptions with the PostHog SDK.

Important: Use your project token which starts with phc_. Do not use a personal API key (which starts with phx_).

You can find your project token in Project Settings (opens in a new tab).

3

Enable instrumentation in Next.js

Required

Note: For Next.js 15 and later, the instrumentation hook is enabled by default. You can skip this step if you’re on Next.js 15+.

Add the following to your next.config.js (or next.config.mjs) to enable the instrumentation hook:

JavaScript

PostHog AI

/** @type {import('next').NextConfig} */
const nextConfig = {
  experimental: {
    instrumentationHook: true,
  },
}
module.exports = nextConfig

4

Create the instrumentation file

Required

Create an instrumentation.ts (or instrumentation.js) file in the root of your project (or inside src/ if you use that folder).

typescript

PostHog AI

import { BatchLogRecordProcessor, LoggerProvider } from '@opentelemetry/sdk-logs'
import { OTLPLogExporter } from '@opentelemetry/exporter-logs-otlp-http'
import { logs } from '@opentelemetry/api-logs'
import { resourceFromAttributes } from '@opentelemetry/resources'
// Create LoggerProvider outside register() so it can be exported and flushed in route handlers
export const loggerProvider = new LoggerProvider({
  resource: resourceFromAttributes({ 'service.name': 'my-nextjs-app' }),
  processors: [
    new BatchLogRecordProcessor(
      new OTLPLogExporter({
        url: 'https://us.i.posthog.com/i/v1/logs',
        headers: {
          Authorization: 'Bearer <ph_project_token>',
          'Content-Type': 'application/json',
        },
      })
    ),
  ],
})
export function register() {
  if (process.env.NEXT_RUNTIME === 'nodejs') {
    logs.setGlobalLoggerProvider(loggerProvider)
  }
}

Note: The loggerProvider is created outside of register() so it can be exported and used to flush logs in route handlers. This pattern is necessary because Route Handlers complete execution before batched logs have a chance to be sent to the collector. By exporting the provider, we can manually flush logs at the end of each request.

Important: The Content-Type: application/json header is required.

Alternatively, you can pass the API key as a query parameter:

typescript

PostHog AI

new OTLPLogExporter({
  url: 'https://us.i.posthog.com/i/v1/logs?token=<ph_project_token>',
  headers: {
    'Content-Type': 'application/json',
  },
})

5

Use OpenTelemetry logging

Required

Now you can use OpenTelemetry logging in your server-side code (API routes, Server Components, etc.):

typescript

PostHog AI

import { SeverityNumber } from '@opentelemetry/api-logs'
import { after } from 'next/server'
import { loggerProvider } from '@/instrumentation'
const logger = loggerProvider.getLogger('my-nextjs-app')
export async function GET() {
  logger.emit({
    body: 'API request received',
    severityNumber: SeverityNumber.INFO,
    attributes: {
      endpoint: '/api/example',
      method: 'GET',
    },
  })
  // Ensure logs are flushed before the serverless function freezes
  after(async () => {
    await loggerProvider.forceFlush()
  })
  return Response.json({ success: true })
}

Important: Without calling forceFlush(), your logs may not be sent. Route Handlers complete execution before the OpenTelemetry batch processor has a chance to send logs to the collector. The after() function from next/server runs code after the response is sent, ensuring logs are flushed before the serverless function freezes.

6

Test your setup

Recommended

Once everything is configured, test that logs are flowing into PostHog:

1. Send a test log from your application
2. Check the PostHog Logs interface for your log entries
3. Verify the logs appear in your project

View your logs in PostHog (opens in a new tab)

Next steps

Checkpoint

What you can do with your logs

Troubleshoot common issues (opens in a new tab)