What is the OPC UA Web API

Table of Contents

Advantages

Functions

Implementation

Use case with manubes

Conclusion

The key advantage of the OPC UA Web API is that it eliminates the need for binary protocols, which are difficult to integrate into web applications. Instead, access via standard protocols such as HTTP/REST enables simple and platform-independent integration.

The Web API is particularly well-suited for web applications that rely on standard technologies and do not require extremely high-performance mass communication.

General information about APIs can be found here: What is an API?

The API is accessed via traditional HTTP calls. Through defined endpoints (API definition), various functions of an OPC UA server can be specifically addressed. Data is exchanged in a human-readable JSON format, which simplifies integration into a wide range of systems and platforms.

Simple Functions, Readable Results

The functions used to retrieve data are clearly defined and easy to understand. The simplest operations are reading and writing. As is typical with OPC UA, writing enables bidirectional data exchange.

The result is returned as readable JSON, which can then be processed by the client. Here is an example of a response to a “read” request.

{
“ResponseHeader”: {
“Timestamp”: “2025-05-19T07:53:27.7067381Z”,
“RequestHandle”: 2
},
“Results”: [
{
“UaType”: 11,
“Value”: 26.33,
“SourceTimestamp”: “2025-05-19T04:28:20.6321852Z”
},
{
“UaType”: 11,
“Value”: 104.11,
“SourceTimestamp”: “2025-05-19T04:28:20.6326211Z”
}
]
}

Creating a client for an OPC UA Web API server is very straightforward. In principle, a simple REST call via HTTP is sufficient. There are also generators available for various programming languages that can convert the OpenAPI specification into client code.

On the server side, things are a bit more complex. Implementation of the API by an OPC UA server vendor will depend on the vendor’s development and release schedule. In principle, a proxy – essentially a converter from OPC UA to OPC UA Web API – could also be a viable solution.

manubes users can utilize the REST Edge Connector to connect to an OPC UA Server through the Web API.

In our example, we use the public OPC UA demo server provided by the OPC Foundation. Using the Web API’s “read” method, we cyclically read two data points and store them in the manubes TimeSeries Storage.

Displaying values

The recorded values are visualized using the TimeSeries view in manubes. This quickly provides transparency regarding the transmitted OPC UA data and its progression over time.

Since the OPC UA Web API is still very new, many use cases are currently still emerging. However, due to its use of standard web technologies, a wide range of clients – from browsers to cloud services – will be able to easily read and process OPC UA data.

The OPC UA Web API combines robust OPC UA technology with modern web standards, without requiring developers to master the complex OPC UA binary protocol.