A neutral, source-cited survey of the WebSocket libraries available to .NET developers in 2026: sgcWebSockets .NET, System.Net.WebSockets, ASP.NET Core SignalR, WebSocket-Sharp, Fleck, and Watson WebSocket. Every feature claim links to the project's own documentation.
A one-paragraph summary of each library, with a link to the official documentation or repository.
eSeGeCe · Commercial
C# component suite mirroring the Delphi product. Same Tsgc* class names, same protocol coverage: WebSocket client and server (TCP and HTTP.SYS), MQTT, AMQP, STOMP, WAMP, HTTP/2, OAuth2, JWT, AI/LLM clients (OpenAI, Anthropic, Gemini, DeepSeek, Grok, Ollama, Mistral, MCP), WebRTC servers, plus the 30+ crypto exchange and SaaS API integrations. Targets .NET Framework 2.0–4.8.1, .NET Core 1.0–3.1, .NET 5/6/7/8/9, and .NET Standard 1.6/2.0.
Microsoft · MIT (part of .NET)
The low-level WebSocket API built into .NET itself. Provides ClientWebSocket for clients and a server abstract WebSocket class consumed by ASP.NET Core, Kestrel, and HttpListener. RFC 6455 framing and per-message-deflate (WebSocketDeflateOptions) are first-class.
Microsoft · MIT (part of ASP.NET Core)
Microsoft's high-level real-time framework. Built on top of WebSocket, Server-Sent Events, and Long Polling (in that fall-back order); exposes a hub RPC API rather than raw frames. JSON or MessagePack hub protocols; scales via Azure SignalR Service or a Redis backplane.
sta.blockhead · MIT
Long-running open-source C# WebSocket client and server. Targets .NET Framework 3.5 and later (and Mono), implements RFC 6455 with per-message-deflate (no context takeover). The GitHub repository has no tagged releases — users typically take the latest master or pin to a commit hash.
Jason Staten / community · MIT
Server-only C# WebSocket library that does not depend on HttpListener or HTTP.SYS — it listens on a raw socket. Has no client side, no HTTP server, and no built-in TLS termination outside the X509 certificate path. Latest tagged release is 0.14.0 from October 2016.
Joel Christner · MIT
Async C# WebSocket client and server with an event-driven API. Targets .NET Framework 4.8 and .NET 7.0. The repository was archived in May 2024 with a note that it has been integrated into Watson Webserver.
A check () means the project documents native support. A dash (—) means the project does not provide it natively. A tilde (~) means partial / via add-on / not explicitly documented — see the Sources section for what we could verify.
| Feature | sgcWebSockets .NET | System.Net.WebSockets | ASP.NET Core SignalR | WebSocket-Sharp | Fleck | Watson WebSocket |
|---|---|---|---|---|---|---|
| WebSocket Client RFC 6455 client | — | |||||
| WebSocket Server RFC 6455 server | ||||||
| TLS 1.3 TLS 1.3 supported by the provided transport | ~ | ~ | ||||
| HTTP/2 Client Native HTTP/2 client (RFC 7540 / 9113) | ~ | — | — | — | — | |
| MQTT MQTT 3.1.1 / 5.0 client built in | — | — | — | — | — | |
| AMQP AMQP 0.9.1 / 1.0 client built in | — | — | — | — | — | |
| STOMP STOMP 1.0 / 1.2 client built in | — | — | — | — | — | |
| WAMP WAMP v1 / v2 client built in | — | — | — | — | — | |
| Server push / streaming Long-lived push or streaming connection | ||||||
| Auto-reconnect Built-in client auto-reconnect / watchdog | — | — | — | — | ||
| per-message-deflate (RFC 7692) WebSocket compression extension | ~ | — | ~ | |||
| Multi-platform Win / macOS / Linux / iOS / Android | ~ | |||||
| Commercial use allowed Licence permits closed-source commercial use | ||||||
| Source code available Library source is visible to the developer | ||||||
| Active maintenance Release or tagged activity in last 12–18 months | ~ | — | — | |||
| Licence model Licence type | Commercial | MIT (part of .NET) | MIT (part of ASP.NET Core) | MIT | MIT | MIT |
Short notes on the API and feature differences if you are switching from one of the libraries above. Not adversarial — just the practical mapping.
System.Net.WebSockets gives you the wire protocol; sgcWebSockets .NET adds MQTT / AMQP / STOMP / WAMP sub-protocols, HTTP/2, auto-reconnect, watchdog, the AI/LLM and exchange-API clients, and the WebRTC server pieces on top. If you wrote a thin wrapper around ClientWebSocket, the migration is mostly a rename plus event-handler porting.
SignalR speaks its own framing protocol over WebSocket. sgcWebSockets implements the SignalR client wire protocol (TsgcWSAPI_SignalR and TsgcWSAPI_SignalRCore), so a Delphi or .NET client built with sgcWebSockets can talk to an existing ASP.NET Core SignalR server. If you are migrating a full SignalR back-end to raw WebSocket, expect to redesign the hub-method dispatch as your own message envelope.
WebSocket-Sharp's WebSocket client and WebSocketServer map closely to sgcWebSockets' TsgcWebSocketClient and TsgcWebSocketServer. Event names differ (OnMessage exists in both; OnError and OnClose have similar signatures). Sub-protocols (MQTT / AMQP / STOMP / WAMP) are sgcWebSockets-only.
Fleck is server-only. If your application has both a Fleck server and a separate client library, sgcWebSockets .NET unifies both. The Fleck handler-based API (WebSocketServer.Start(socket => ...)) maps to sgcWebSockets' event-based TsgcWebSocketServer with OnMessage / OnConnect handlers.
The Watson client/server event surface (MessageReceived, ClientConnected, ClientDisconnected) maps cleanly to sgcWebSockets' OnMessage / OnConnect / OnDisconnect. Sub-protocols and the AI/LLM API clients are sgcWebSockets-only.
Each cell in the matrix above traces to one of these official documentation pages, repositories, or release notes. All URLs were HEAD-checked at the time of writing.