OCPP API

OCPP integration documentation

Technical instructions for installers and developers to connect OCPP chargers to Joulo's Central System Management Server (CSMS).

OCPP 1.6J
WebSocket
SHA-256

// connection

WebSocket endpoint

URL format

wss://ocpp.joulo.nl/<charge_point_id>?auth=<security_secret>
charge_point_idUnique ID of your charger • assigned during registration in the Joulo dashboard.
security_secret20-digit automatically generated secret. Available in the charger panel after connection.

// messages

Supported OCPP messages

BootNotification
CP → CSMS

Registration on connection • vendor, model, firmware

Heartbeat
CP → CSMS

Periodic status check • every 60 seconds

StatusNotification
CP → CSMS

Connector status: Available, Charging, Faulted

StartTransaction
CP → CSMS

Start charging session with meter value

StopTransaction
CP → CSMS

End session, final meter reading and reason

MeterValues
CP → CSMS

Intermediate energy measurements (Wh)

Authorize
CP → CSMS

User authorization • always accepted

DataTransfer
CP ↔ CSMS

Vendor-specific messages

// security

Authentication & security

Each charger receives a unique 20-digit security secret at registration. This secret:

  • is stored with your registration, so you can look up the connection URL again later • only your own account can read it (Row Level Security)
  • travels over an encrypted WebSocket (wss://)
  • stays visible in your dashboard • replace it and the old value stops working immediately

The gateway validates every connection by comparing SHA-256 of the presented secret against the hash on your registration. Connections without a valid secret are rejected. Every message is validated against the OCPP 1.6J schema.

// configuration

Configuration per brand

OCPP settings are located in different places per brand. After connecting your charger in the Joulo dashboard, you'll receive step-by-step instructions specific to your brand.

Web interface

Many chargers have a built-in web server (e.g. 192.168.x.x) where you configure the OCPP URL.

Manufacturer app

Some brands (Alfen, EVBox) offer an app or cloud portal where you set the OCPP backend URL.

Installer

In some installations, the installer configures the OCPP settings during mounting.

Tip: set WebSocketPingInterval to 60 seconds. Some brands (including Alfen) ship with a 10-second default, which generates unnecessary traffic and causes false disconnects on flaky connections.

Related pages

Joulo for developers

Overview of all tools, APIs and integrations.

OCPP connection

Connect any OCPP 1.6J charger to Joulo.

OCPP API

OCPP WebSocket integration and configuration.

Home Assistant

Sensors, lovelace and automations via the REST API.

Platform status

Realtime status of all Joulo services.

Developer Docs

Quickstart, authentication, guides and REST API reference.

status.joulo.nl

Realtime status of all Joulo services.

Ready to get started?

Create a free account and connect your charger. Find your API token directly in the dashboard.

Sign up freeAPI docs