In modern industrial automation, OPC UA (Open Platform Communications Unified Architecture) has become the global standard for secure and reliable data exchange between machines, software, and industrial systems.
To interact with OPC UA servers, engineers use OPC UA client software. These tools allow users to browse server nodes, monitor real-time data, test connectivity, and troubleshoot communication issues.
Fortunately, several free OPC UA clients are available that provide powerful features without requiring expensive licenses.
This guide covers:
- What OPC UA clients are
- Why engineers rely on free OPC UA clients
- The best free OPC UA clients available today
- How to choose the right OPC UA client for your needs
Table of Contents
What Is an OPC UA Client?
An OPC UA client is software designed to connect to an OPC UA server and interact with its data.
In a typical industrial system:
- OPC UA Server → exposes data from devices, PLCs, sensors, or machines
- OPC UA Client → reads, writes, and monitors that data
OPC UA clients allow engineers to:
- Browse the server’s address space
- Monitor live industrial data
- Call server methods
- Subscribe to data changes
- Configure security certificates
These tools are widely used across industries including manufacturing, energy, oil & gas, utilities, and Industrial IoT (IIoT).
Why Engineers Use Free OPC UA Clients
Free OPC UA clients are extremely useful for both beginners and experienced automation professionals.
Testing OPC UA Servers
Before deploying a system, engineers often test whether an OPC UA server is working correctly. Free clients allow quick verification of server functionality.
Troubleshooting Communication
OPC UA clients help diagnose issues such as:
- Connection failures
- Certificate errors
- Incorrect node configuration
- Security mismatches
Learning OPC UA
Students and developers often use free OPC UA clients to understand:
- OPC UA architecture
- Data models
- Security configuration
Quick Diagnostics
Instead of installing a full SCADA system, engineers can use lightweight OPC UA clients for fast diagnostics and monitoring.
Best Free OPC UA Clients
Below are some of the most widely used free OPC UA client tools in the industrial automation industry.
UaExpert
UaExpert is a full-featured OPC UA client application developed by Unified Automation. It serves as a general-purpose test and diagnostic tool for connecting to OPC UA servers, exploring their address spaces, and verifying data communication. Widely used in industrial automation, UaExpert helps engineers test interoperability and validate system configurations.
Key facts
- Developer: Unified Automation GmbH
- Type: OPC UA client and test tool
- Platforms: Windows (64-bit), Linux
- License: Freeware (registration required)
- Primary uses: Data monitoring, method calls, event handling, and diagnostics
Functionality and features
UaExpert demonstrates the capabilities of Unified Automation’s C++ OPC UA Client SDK. It enables browsing of server address spaces, reading and writing node values, invoking methods, and managing subscriptions for real-time monitoring. The software supports major OPC UA service sets, including Data Access, Alarms & Conditions, Historical Access, and Method invocation. Advanced plugins expand its scope to tasks like XML NodeSet export, performance testing, and data logging.
Architecture and user interface
Built with the Qt framework, UaExpert provides a modular, plugin-based interface. Its main panes include:
- Project pane: Lists connected servers and open documents.
- Address Space pane: Displays the hierarchical information model of the server.
- Attribute and Reference panes: Show details of selected nodes.
- Central view area: Hosts specialized views such as DataAccess, Alarms, and Historical Trend.
Industrial use and interoperability
UaExpert is frequently used to verify connections to devices and systems like Siemens S7-1500 or ABB AC500 controllers. It assists developers in testing OPC UA implementations, diagnosing communication errors, and validating security configurations such as certificate exchanges and encryption modes. Its combination of free availability and full OPC UA compliance makes it a standard reference tool for engineers working with industrial communication and control systems.
Prosys OPC UA Client
Prosys OPC UA Client is a desktop software tool used to connect to, explore, and test OPC UA servers in industrial automation systems. It is designed for engineers, integrators, and developers who need to validate OPC UA connectivity, data, and security during development, commissioning, and troubleshooting.
Key facts
- Vendor: Prosys OPC Ltd (formerly Prosys PMS Ltd)
- Purpose: Test and explore OPC UA servers and data models
- Typical users: Automation engineers, system integrators, OPC UA developers
- Main platform: Desktop (Windows; some tools also on macOS via Browser)
- Related products: Prosys OPC UA Browser, Simulation Server, Monitor
Core capabilities
Prosys OPC UA Client can discover and connect to OPC UA servers, list available endpoints, and let users select security modes and policies. Once connected, it allows browsing of the server’s address space, viewing node attributes, and organizing items in the client workspace. Users can read and write values, either on demand or cyclically, and configure subscriptions to monitor data changes and receive events in real time.
The client also supports calling server-side methods and accessing historical data if the server provides it. This makes it useful for testing complete OPC UA information models, not just live process values.
Security and diagnostics
The software implements OPC UA’s built-in security model with certificate management, encryption, and user authentication options. Engineers can quickly test different security settings, verify that secure endpoints work as expected, and inspect failures using integrated logs and diagnostics views.
This combination of security handling and detailed logging makes the client well suited for troubleshooting connectivity issues between OT devices and higher-level systems like SCADA, historians, or IIoT platforms.
Position in the Prosys product family
Prosys OPC UA Client is one of several OPC UA–related tools from Prosys OPC Ltd, alongside products such as Prosys OPC UA Browser, Simulation Server, and Monitor. Together, they cover browsing, simulation, visualization, and data collection use cases across OPC UA-based architectures.
FreeOpcUa (Open Source)
FreeOpcUa is an open-source suite of libraries and tools that implement the OPC UA (IEC 62541) protocol for industrial data exchange. It provides client and server functionality across multiple programming languages, enabling interoperable communication between industrial devices and software systems.
Key facts
- Languages: C++, Python, and Rust
- License: LGPL-3.0 (core libraries), GPL-3.0 (GUI tools)
- Primary repositories:
freeopcua,python-opcua,opcua-asyncio,opcua-client-gui,opcua-modeler - Focus: Industrial automation, IIoT, and Industry 4.0 integration
Core components
The project began with a C++ library offering a full OPC UA client and server implementation, including browsing, reading/writing variables, subscriptions, and event handling. Python and Rust variants later extended accessibility:
python-opcua– a pure Python synchronous library for rapid prototyping and integration.opcua-asyncio(AsyncUA) – an asynchronous Python ≥ 3.7 successor leveragingasynciofor concurrency and better scalability.freeopcuaC++ – the original high-performance implementation supporting both Linux and Windows builds.
Graphical and modeling tools
FreeOpcUa also includes utilities that simplify interaction with OPC UA networks:
opcua-modeler– a GUI for creating and exporting OPC UA address-space models as XML, suitable for code generation or use with other SDKs.opcua-client-gui– a PyQt-based graphical client supporting browsing, subscriptions, and variable writes, designed for testing and diagnostics.
Ecosystem and usage
All libraries share autogenerated code derived from OPC UA XML schemas to maintain protocol compliance. Typical applications include building industrial gateways, simulation servers, or test clients in research and manufacturing contexts. The tools interoperate with commercial and open-source OPC UA stacks such as Prosys, UaExpert, and open62541.
Current status
Development continues across several active repositories under the GitHub organization “FreeOpcUa.” While the original python-opcua package is deprecated, the asynchronous opcua-asyncio library is maintained as its modern replacement, keeping FreeOpcUa relevant for contemporary IIoT and automation projects.
Softing OPC UA Client
Softing AG is a German technology company that develops and markets hardware and software solutions for industrial automation, automotive electronics, and IT networks. Founded in 1979 and headquartered in Haar near Munich, it is publicly listed on the Frankfurt Stock Exchange under the ticker SYT. The company operates globally through specialized subsidiaries.
Key facts
- Founded: 1979
- Headquarters: Haar, Germany
- Stock symbol: SYT (Xetra, Frankfurt)
- CEO: Dr. Wolfgang Trier
- Employees: Approximately 410 (2023)
- Business segments: Industrial, Automotive, IT Networks
Business structure and focus
Softing AG functions as a management holding overseeing three key segments.
Softing Industrial Automation provides communication interfaces and software for connecting machines and systems in manufacturing and process industries. Its products support industrial protocols such as PROFIBUS, PROFINET, Ethernet/IP, and CAN, helping enable digitalization and Industry 4.0 solutions.
Softing Automotive Electronics specializes in diagnostic, measurement, and testing tools for electronic control units (ECUs) across the entire vehicle lifecycle—from engineering to production and after-sales service.
Softing IT Networks designs measurement and certification equipment for copper and fiber-optic cabling in enterprise and industrial IT infrastructures, ensuring high data integrity and network performance.
Market presence and partnerships
Softing serves customers in more than 60 countries, with particular strength in Europe, North America, and Asia. The company’s joint venture, Softing Technology Shanghai, strengthens its automotive presence in China, addressing the growing demand for diagnostic systems in electric and autonomous vehicles. Its clients include manufacturers, system integrators, and industrial automation firms worldwide.
Recent developments
Softing continues to invest in connectivity technologies for smart factories and software-defined vehicles. In 2022, its automotive division secured a multimillion-euro contract to supply diagnostic and parameterization systems for a global premium automaker’s production lines, highlighting its competitiveness in high-value automotive manufacturing solutions.
Matrikon OPC Explorer
Matrikon OPC Explorer is a free OPC client software used to test, troubleshoot, and validate communication with OPC (OLE for Process Control) servers. It is one of the most widely used diagnostic tools in industrial automation, enabling engineers to verify data access and connectivity between control systems, devices, and applications.
Key facts
- Developer: Matrikon (a Honeywell brand)
- Latest version: 5.4.1.0 (as of 2024)
- Supported systems: Windows 7 through Windows 11
- License: Freeware
- Supported standards: OPC DA 1.0a–2.05a, HDA, A&E, and Security 1.0
Function and features
Matrikon OPC Explorer acts as a comprehensive testing client for multiple OPC specifications—Data Access (DA), Historical Data Access (HDA), and Alarms & Events (A&E). It allows users to browse server address spaces, monitor real-time data values, and perform read/write operations to validate bidirectional communication. The tool also supports load testing and DCOM configuration verification for remote server connections.
Technical capabilities
The application identifies which OPC interfaces a server implements and displays them in a tree-view browser. It supports synchronous and asynchronous data exchanges, array handling, and security authentication per the OPC Security 1.0 specification. Its lightweight installer enables setup and connection testing in under five minutes, making it suitable for rapid deployment in plant environments.
Use in automation
Widely deployed across industries such as energy, manufacturing, and process control, Matrikon OPC Explorer helps ensure the reliability of data exchange between devices and supervisory systems. It is often paired with tools like the Matrikon OPC Simulation Server for safe validation without affecting live operations, forming part of Matrikon’s suite of free OPC diagnostic utilities.
Key Features to Look for in an OPC UA Client
When selecting a free OPC UA client, consider the following capabilities.
Node Browsing
Allows exploration of the server’s address space to locate variables, objects, and methods.
Data Monitoring
Real-time monitoring of values from industrial devices and sensors.
Subscription Support
Receive automatic updates when monitored values change.
Security Configuration
Important for testing OPC UA security modes such as:
- None
- Sign
- Sign & Encrypt
Certificate Management
Essential for secure communication between clients and servers.
Free OPC UA Clients vs Paid Solutions
| Feature | Free Clients | Paid Clients |
|---|---|---|
| Basic browsing | ✔ | ✔ |
| Data monitoring | ✔ | ✔ |
| Subscription support | ✔ | ✔ |
| Advanced diagnostics | Limited | ✔ |
| Technical support | Community | ✔ |
| Industrial integration | Limited | ✔ |
Free OPC UA clients are typically sufficient for testing, diagnostics, and development, while enterprise deployments may require commercial platforms.
When Should You Use a Free OPC UA Client?
Free OPC UA clients are ideal when:
- Testing new OPC UA servers
- Learning OPC UA architecture
- Debugging communication issues
- Monitoring industrial data
- Developing IIoT applications
Many automation engineers keep multiple OPC UA clients installed to handle different diagnostic tasks.
Conclusion
OPC UA clients are essential tools for interacting with industrial communication systems. Whether you are testing a server, troubleshooting connectivity, or developing Industrial IoT solutions, free OPC UA client software provides powerful capabilities without additional cost.
Tools such as UaExpert, Prosys OPC UA Client, FreeOpcUa, and Matrikon OPC Explorer have become standard utilities for automation engineers around the world.
By choosing the right OPC UA client, engineers can quickly analyze server data, diagnose issues, and build reliable industrial communication systems.