A gateway connects to the cloud first (MQTT / Waveshare). Modbus devices are attached behind it. OCPP wallboxes live on the other tab and link here for site load only.

Local: mqtt://localhost:1883 (monorepo python-mqtt). Cloud TLS: host mqtt.ems-dev… + port 8883 → auto mqtts:// (self-signed OK in this sim). Copy Sub/Pub from EMS wizard when targeting cloud. LWT on {base}/lwt with birth 0x01 / will 0x00.

The charge point WebSocket runs in this browser tab (closing or removing it disconnects the wallbox). Point it at local ws://localhost:9000/<ocppSecret> or a deployed wss://…/<ocppSecret>. Gateway is optional — pick one only to couple EV load into Modbus inverter/meter registers. HTTPS pages cannot open ws://localhost (mixed content); use npm run site locally for a local CSMS.