Reference

The OPC UA reference

Everything on this site that is not a course. Free, open, no account needed, no registration wall. The specification itself is published by the OPC Foundation; this is the explanatory layer around it.

Status codes

What the code means, why it happened, and the fix: in diagnostic order.

127 pages →

Glossary

One concept per page, defined precisely, with the mistake people make.

134 pages →

IEC 62541 parts

What each numbered part of the specification governs, and whether you need it.

32 pages →

Companion models

DI, Machinery, MachineTool, PackML and the rest: with real type names.

52 pages →

SDKs and code

The same twelve tasks in every stack, pinned to a version, runnable against a public server.

10 pages →

Tools

Clients, simulators, model editors and diagnostics.

20 pages →

Integrations

PLCs, SCADA, brokers, historians and cloud: with the licensing traps.

17 pages →

Comparisons

OPC UA against MQTT, Modbus and OPC Classic, without a side to sell.

3 pages →

Last verified 7 September 2026 against OPC UA 1.05.07. OPC UA Connect is an educational resource and is not affiliated with the OPC Foundation.