OPC UA Pub/Sub supports two encodings: Binary (compact and fast, about 30% of the payload size of JSON) and JSON (human-readable, debug-friendly, easy to integrate with web and REST stacks). The choice depends on the performance versus interoperability trade-off.

Binary encoding shrinks payloads to roughly 30% of the JSON size and parses very quickly, but it is hard to debug without a Wireshark dissector or an equivalent tool. JSON is verbose but parses with any standard library and can be inspected with curl, Postman or a browser. The typical split is Binary for machine-to-machine traffic where performance dominates, and JSON for IT and IoT integrations where readability and cross-language compatibility matter more. The two encodings can coexist within the same installation, attached to different transports.

When debugging a stuck Pub/Sub pipeline, temporarily switch one publisher to JSON: a five-minute capture in any text tool will save you hours of binary trace reading.