Opc.Ua.WebApi - the C# library for the OPC UA Web API

November 8, 2025 · View on GitHub

Provides simple HTTPS based access to an OPC UA server.

This C# SDK is automatically generated by the OpenAPI Generator project:

API version: 1.05.4
SDK version: 15.6.0
Generator version: 7.15.0
Build package: org.openapitools.codegen.languages.CSharpClientCodegen

Frameworks supported

.NET Core >=1.0
.NET Framework >=4.6
Mono/Xamarin >=vNext

Dependencies

Json.NET - 13.0.2 or later
JsonSubTypes - 1.8.0 or later
System.ComponentModel.Annotations - 5.0.0 or later

The DLLs included in the package may not be the latest version. We recommend using NuGet to obtain the latest version of the packages:

Install-Package Newtonsoft.Json
Install-Package JsonSubTypes
Install-Package System.ComponentModel.Annotations

Installation

Generate the DLL using your preferred tool (e.g. dotnet build)

Then include the DLL (under the bin folder) in the C# project, and use the namespaces:

using Opc.Ua.WebApi.Api;
using Opc.Ua.WebApi.Client;
using Opc.Ua.WebApi.Model;

Usage

To use the API client with a HTTP proxy, setup a System.Net.WebProxy

Configuration c = new Configuration();
System.Net.WebProxy webProxy = new System.Net.WebProxy("http://myProxyUrl:80/");
webProxy.Credentials = System.Net.CredentialCache.DefaultCredentials;
c.Proxy = webProxy;

Connections

Each ApiClass (properly the ApiClient inside it) will create an instance of HttpClient. It will use that for the entire lifecycle and dispose it when called the Dispose method.

To better manager the connections it's a common practice to reuse the HttpClient and HttpClientHandler (see here for details). To use your own HttpClient instance just pass it to the ApiClass constructor.

HttpClientHandler yourHandler = new HttpClientHandler();
HttpClient yourHttpClient = new HttpClient(yourHandler);
var api = new YourApiClass(yourHttpClient, yourHandler);

If you want to use an HttpClient and don't have access to the handler, for example in a DI context in Asp.net Core when using IHttpClientFactory.

HttpClient yourHttpClient = new HttpClient();
var api = new YourApiClass(yourHttpClient);

You'll loose some configuration settings, the features affected are: Setting and Retrieving Cookies, Client Certificates, Proxy settings. You need to either manually handle those in your setup of the HttpClient or they won't be available.

Here an example of DI setup in a sample web project:

services.AddHttpClient<YourApiClass>(httpClient =>
   new PetApi(httpClient));

Getting Started

using System.Collections.Generic;
using System.Diagnostics;
using System.Net.Http;
using Opc.Ua.WebApi.Api;
using Opc.Ua.WebApi.Client;
using Opc.Ua.WebApi.Model;

namespace Example
{
    public class Example
    {
        public static void Main()
        {

            Configuration config = new Configuration();
            config.BasePath = "http://localhost:4840";
            // create instances of HttpClient, HttpClientHandler to be reused later with different Api classes
            HttpClient httpClient = new HttpClient();
            HttpClientHandler httpClientHandler = new HttpClientHandler();
            var apiInstance = new DefaultApi(httpClient, config, httpClientHandler);
            var activateSessionRequest = new ActivateSessionRequest(); // ActivateSessionRequest | [Link to specification](https://reference.opcfoundation.org/v105/Core/docs/Part4/5.7.3/#5.7.3.2). (optional) 

            try
            {
                ActivateSessionResponse result = apiInstance.ActivateSession(activateSessionRequest);
                Debug.WriteLine(result);
            }
            catch (ApiException e)
            {
                Debug.Print("Exception when calling DefaultApi.ActivateSession: " + e.Message );
                Debug.Print("Status Code: "+ e.ErrorCode);
                Debug.Print(e.StackTrace);
            }

        }
    }
}

Documentation for API Endpoints

All URIs are relative to http://localhost:4840

Class	Method	HTTP request
DefaultApi	ActivateSession	POST /activatesession
DefaultApi	Browse	POST /browse
DefaultApi	BrowseNext	POST /browsenext
DefaultApi	Call	POST /call
DefaultApi	Cancel	POST /cancel
DefaultApi	CloseSession	POST /closesession
DefaultApi	CreateMonitoredItems	POST /createmonitoreditems
DefaultApi	CreateSession	POST /createsession
DefaultApi	CreateSubscription	POST /createsubscription
DefaultApi	DeleteMonitoredItems	POST /deletemonitoreditems
DefaultApi	DeleteSubscriptions	POST /deletesubscriptions
DefaultApi	FindServers	POST /findservers
DefaultApi	GetEndpoints	POST /getendpoints
DefaultApi	HistoryRead	POST /historyread
DefaultApi	HistoryUpdate	POST /historyupdate
DefaultApi	ModifyMonitoredItems	POST /modifymonitoreditems
DefaultApi	ModifySubscription	POST /modifysubscription
DefaultApi	Publish	POST /publish
DefaultApi	Read	POST /read
DefaultApi	RegisterNodes	POST /registernodes
DefaultApi	Republish	POST /republish
DefaultApi	SetMonitoringMode	POST /setmonitoringmode
DefaultApi	SetPublishingMode	POST /setpublishingmode
DefaultApi	SetTriggering	POST /settriggering
DefaultApi	TransferSubscriptions	POST /transfersubscriptions
DefaultApi	TranslateBrowsePathsToNodeIds	POST /translate
DefaultApi	UnregisterNodes	POST /unregisternodes
DefaultApi	Write	POST /write

Documentation for Models

Documentation for Authorization

Endpoints do not require authorization.