dotnet/website/articles/Agent-overview.md
Agent is one of the most fundamental concepts in AutoGen.Net. In AutoGen.Net, you construct a single agent to process a specific task, and you extend an agent using Middlewares, and you construct a multi-agent workflow using GroupChat.
[!NOTE] Every agent in AutoGen.Net implements @AutoGen.Core.IAgent, for agent that supports streaming reply, it also implements @AutoGen.Core.IStreamingAgent.
To chat with an agent, typically you can invoke @AutoGen.Core.IAgent.GenerateReplyAsync*. On top of that, you can also use one of the extension methods like @AutoGen.Core.AgentExtension.SendAsync* as shortcuts.
[!NOTE] AutoGen provides a list of built-in message types like @AutoGen.Core.TextMessage, @AutoGen.Core.ImageMessage, @AutoGen.Core.MultiModalMessage, @AutoGen.Core.ToolCallMessage, @AutoGen.Core.ToolCallResultMessage, etc. You can use these message types to chat with an agent. For further details, see built-in messages.
Send a @AutoGen.Core.TextMessage to an agent via @AutoGen.Core.IAgent.GenerateReplyAsync*: [!code-csharp]
Send a message to an agent via @AutoGen.Core.AgentExtension.SendAsync*: [!code-csharp]
If an agent implements @AutoGen.Core.IStreamingAgent, you can use @AutoGen.Core.IStreamingAgent.GenerateStreamingReplyAsync* to chat with the agent in a streaming way. You would need to process the streaming updates on your side though.
@AutoGen.Core.IMiddleware and @AutoGen.Core.IStreamingMiddleware are used to extend the behavior of @AutoGen.Core.IAgent.GenerateReplyAsync* and @AutoGen.Core.IStreamingAgent.GenerateStreamingReplyAsync*. You can register middleware to an agent to customize the behavior of the agent on things like function call support, converting message of different types, print message, gather user input, etc.
You can construct a multi-agent workflow using @AutoGen.Core.IGroupChat. In AutoGen.Net, there are two type of group chat: @AutoGen.Core.SequentialGroupChat: Orchestrates the agents in the group chat in a fix, sequential order. @AutoGen.Core.GroupChat: Provide more dynamic yet controllable way to orchestrate the agents in the group chat.
For further details, see Group chat overview.