SignalR for C# (.NET): Complete Guide with Examples

What is SignalR and why is it needed?

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SignalR is a library for ASP.NET Core that simplifies adding real-time features to web applications. It allows the server to instantly send data to connected clients (browsers, mobile applications, desktop applications) without the need for constant requests from the client.

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Why is this needed? The traditional HTTP protocol works on a "request-response" principle: the client sends a request, the server responds. To receive updates, the client must constantly poll the server (polling). This is inefficient and creates delays. SignalR solves this problem by providing a persistent two-way connection.

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Main use cases:

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• Chats and messengers (instant message delivery)
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• Monitoring panels and dashboards (updating currency rates, stock quotes)
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• Collaborative document editing (Google Docs-like)
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• Real-time notifications (new orders, alerts)
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• Multiplayer games
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• Progress of long-running operations (file uploads, data processing)
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SignalR automatically selects the best transport protocol for the connection:

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• WebSocket — the most efficient, persistent two-way connection
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• Server-Sent Events (SSE) — one-way transmission from server to client
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• Long Polling — fallback mechanism if WebSocket and SSE are unavailable
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Installing SignalR

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Server-side installation (ASP.NET Core)

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For the server side, use the NuGet package. Run in the terminal:

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dotnet add package Microsoft.AspNetCore.SignalR

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Or via Package Manager Console in Visual Studio:

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Install-Package Microsoft.AspNetCore.SignalR

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Installing the client for JavaScript (browser)

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For the client side (browser), use npm:

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npm install @microsoft/signalr

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Or include via CDN:

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<script src="https://cdnjs.cloudflare.com/ajax/libs/microsoft-signalr/8.0.0/signalr.min.js"></script>

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Installing the client for .NET (C#)

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For a C# client (e.g., console application or WPF):

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dotnet add package Microsoft.AspNetCore.SignalR.Client

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Quick start: "Hello, World!" example

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Let's create a simple chat: the server receives a message and broadcasts it to all connected clients.

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Step 1: Create a Hub (server side)

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Create a file ChatHub.cs:

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using Microsoft.AspNetCore.SignalR;\n\nnamespace SignalRChat.Hubs\n{\n    public class ChatHub : Hub\n    {\n        public async Task SendMessage(string user, string message)\n        {\n            // Send the message to all connected clients\n            await Clients.All.SendAsync("ReceiveMessage", user, message);\n        }\n    }\n}\n

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Step 2: Register SignalR in Program.cs

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using SignalRChat.Hubs;\n\nvar builder = WebApplication.CreateBuilder(args);\n\n// Add SignalR\nbuilder.Services.AddSignalR();\n\nvar app = builder.Build();\n\napp.MapGet("/", () => "Hello World!");\n\n// Map the hub to the /chatHub path\napp.MapHub<ChatHub>("/chatHub");\n\napp.Run();\n

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Step 3: Create a client (HTML + JavaScript)

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<!DOCTYPE html>\n<html>\n<head>\n    <title>SignalR Chat</title>\n</head>\n<body>\n    <h2>SignalR Chat</h2>\n    <div>\n        <input type="text" id="userInput" placeholder="Your name" />\n        <input type="text" id="messageInput" placeholder="Message" />\n        <button onclick="sendMessage()">Send</button>\n    </div>\n