August 11, 2026 · How-To

How to Browse an OPC UA Server Address Space

An OPC UA server is self-describing: it will hand you its entire structure if you ask. The asking is called browsing, and it is the first thing you do after connecting. Browse is what turns a server from an opaque endpoint into a navigable tree of objects, variables, and methods — and it is how you find the variables worth reading or subscribing to without an external tag list.

This guide walks through the full browse flow: connect, pick an endpoint, open a session, walk the address space, read a value. For the structure you are browsing, see the information model; for going further than reads, subscriptions.

Step 1 — Connect and Discover Endpoints

A UA server is reached at an opc.tcp:// URL, typically port 4840 (e.g. opc.tcp://192.168.1.10:4840). The first call is GetEndpoints, which returns every endpoint the server offers along with its security mode and policy. You pick the one matching your security requirements (see UA security).

Step 2 — SecureChannel and Session

With an endpoint chosen, you open a SecureChannel (the encrypted transport) and then a Session (the application-level context that holds subscriptions and state). At session creation you may authenticate as a user if the server requires it. From here on, every service call — Browse, Read, Subscribe — runs inside this session.

Step 3 — Browse From a Root Node

Browsing starts from a node and returns its children plus the reference types linking them. The standard starting points:

• Objects folder — where the server's exposed instances live. Almost everything you want is under here.
• Server object — standard server status, diagnostics, capabilities, and the namespace array.
• Types folder — the type system (object types, data types, reference types).

From Objects you follow HasComponent, Organizes, and HasProperty references down into the vendor's hierarchy: Objects → Line1 → Motor3 → Speed.

Step 4 — Read or Subscribe

Once you have a Variable's NodeId, you Read its current value (with status code and timestamp) or, better, subscribe so the server pushes changes — see monitored items. Reads are for snapshots; subscriptions are for live data.

Tips

• Filter by node class when browsing large servers to find Variables fast without expanding every Object.
• Use the namespace array (in the Server object) to decode NodeId namespace indices into vendor namespaces.
• Read the DataType attribute before reading the value so you decode the bytes correctly.
• Cheaper than polling: once you know what you want, subscribe rather than read in a loop.

Browsing on macOS

MacTools OPC UA Explorer handles every step — endpoint discovery, SecureChannel/session, certificate trust, and an interactive address-space tree you expand and read from. You browse, click a variable, and read or subscribe. Native macOS; no Windows, no DCOM.

Frequently Asked Questions

How do I browse an OPC UA server?

Connect to the server URL (opc.tcp://host:port), discover the endpoints it offers and pick one with the security mode you want, establish a SecureChannel and open a Session, then call Browse starting at a root node (typically ObjectsFolder). Browse returns child nodes and the reference types that link them, so you walk the address space as a tree of objects, variables, and methods until you find the variable you want to read or subscribe to.

What OPC UA URL scheme do servers use?

OPC UA binary endpoints use the opc.tcp:// scheme, for example opc.tcp://192.168.1.10:4840. HTTP-based endpoints use https:// but the binary opc.tcp transport is by far the most common for industrial servers. The default port is 4840.

Where do I start browsing in an OPC UA server?

Start at the Objects folder (the standard node that holds the server's exposed instances). From there, follow HasComponent and Organizes references into the vendor's object hierarchy. The Server object (sibling of Objects) holds standard server diagnostics, status, and capabilities. Most data you care about lives under Objects.

Can I browse an OPC UA server from macOS?

Yes. MacTools OPC UA Explorer connects to any opc.tcp:// endpoint on macOS, lists endpoints and security modes, opens a session, and lets you browse the address space as a tree — reading values and subscribing to variables without Windows or DCOM.

Further Reading

• OPC UA Information Model Explained
• OPC UA Subscriptions and Monitored Items
• OPC UA Security: Certificates and Encryption
• OPC UA vs OPC Classic (DA)