MCP, A2A, and AG-UI: Architecting Agent Intelligence Beyond Chat MLCon Berlin 2026 Max Marschall @MaxOSchulte Consultant / Architect @ Thinktecture 

Model Context Protocol (MCP) In this Session The Agent–User Interaction (AG-UI) Protocol Agent-to-Agent Protocol (A2A) 

The Model Context Protocol Think of MCP like a USB-C port for AI applications. [...] MCP provides a standardized way to connect AI applications to external systems. https://modelcontextprotocol.io/docs/getting-started/intro 

HOST • LLM applications (Claude Desktop, IDEs) that initiate connections The Model Context Protocol CLIENT • 1:1 connection handler inside host, manages protocol communication SERVER • Provides context, tools, and capabilities to clients • Servers can't talk to each other 

• Do not repeat your self • (KISS) • No standardization across implementations • Fragile when systems change Why should we care? 

M x N ➡ M+N App 1 App 3 App 2 Database Documentation FAQ App 1 App 3 App 2 Database Documentation FAQ MCP M AI Applications N Tools, Ressources, Prompts ➡ 

• Build once, connect everywhere • Open-source and vendor-neutral • Based on proven patterns The MCP Idea 💡 

The Model Context Proctocol 

The Model Context Proctocol 

The Model Context Proctocol 

• Tools • Ressources • Prompts • Elicitation • Sampling • Server Composition • Progress Report Features More to come (e.g. MCP-UI) 

... is the ability to connect a large language model (LLM) to reliable sources of information to ensure accurate and relevant results. • Improves relevance • Prevents hallucinations • Connects to real-world • Alternatives: Retrievel-Augmented Generation (RAG) & Fine-Tuning Grounding 

... is to provide an automated way to add concise contextual information based on the changing requirements. Examples: • Web search / web access • Documentation access Context-Hydration 

https://modelcontextprotocol.info/docs/clients/ Feature Support Missing features Clients from MCP proposer 

• Limit your tools • Scope your tools • Tool compatibility • Feature compatibility Best Practices 

• Different tools by authentication / authorization • Update tool lists depending on preceding queries • Agent Skill enable / disable MCPs • Tool change (command) Context Size Solution: Dynamic Tools 

• Async-Tools • MCP-UI • Code execution • (Antrophic / Claude) Agent Skills + MCP = RAG-MCP. Not “more tools,” but a better relationship to tools Outlook 

Agent-to-Agent Protocol Model Context Protocol (MCP) The Agent–User Interaction (AG-UI) Protocol Agent-to-Agent Protocol (A2A) 

A2A An open standard enabling secure, interoperable communication between autonomous AI agents across diverse frameworks and platforms 

• Invented by Google • Gifted to Linux Foundation • "Build with ADK (or any framework), equip with MCP (or any tool), and communicate with A2A, to remote agents, local agents, and humans." A2A Origins https://a2a-protocol.org/latest/ 

Partners https://developers.googleblog.com/en/a2a-a-new-era-of-agent-interoperability/ 

A2A Layer https://a2a-protocol.org/latest/ 

• A2A treats agents as standard enterprise applications, relying on established web security practices. Identity handled at HTTP transport layer. • Production deployments MUST use HTTPS • OAuth 2.0, OpenID Connect, API Keys, Manual TLS • OpenAPI Aligned: Follows OpenAPI Security Scheme speci fi cation • Server Responsibility: Authenticate every request • In-Task Auth: Use auth-required state for secondary credentials during task execution Security & Authentication 

Goals Interoperability Bridge communication gaps between disparate agentic systems Discovery Enterprise-grade secure communication patterns Security Enterprise-grade secure communication patterns Collaboration Enable agents to delegate tasks, exchange context, work together 

• Simple: Reuses HTTP, JSON-RPC 2.0, Server-Sent Events • Enterprise Ready: Auth, security, privacy, tracing, monitoring built-in • Async First: Designed for long-running tasks, human-in-the-loop • Modality Agnostic: Text, audio/video, structured data, embedded UI • Opaque Execution: No need to share internal thoughts, plans, or tools Guiding Principles 

Client • Discover agents via Agent Cards • Authenticate requests • Send messages / create tasks • Handle streaming responses • Expose webhook for noti fi cations Client Agent vs Remote Agent Remote • Publish Agent Card /.well - known/agent - card.json • Authenticate incoming requests • Process tasks & generate artifacts • Stream responses via SSE • Send push noti fi cations 

Core Concepts 1. Agent Card Metadata, self-describing manifest 2. Task Stateful work unit, lifecycle, contains status, history and artifacts 3. Message Message ("user" / "agent"), 1-X parts, conversation history 4. Part Smallest Unit, TextPart, FilePart, DataPart 5. Artifact Generated result output, composed parts 6. Context Identi fi er to group tasks, maintains state across interactions 

Agent Card https://a2a-protocol.org/latest/tutorials/python/3-agent-skills-and-card/#agent-skills 

• id Unique task identi fi er • contextId Grouping identi fi er • status Current TaskStatus submitted ➡ working ➡ completed / failed / canceled / rejected • Interrupts: input-required & auth-required • history Message array • artifacts Generated outputs • metadata Extension data Task 

• tasks/send - Submit task message to agent • tasks/get - Retrieve task status • tasks/cancel - Cancel running task • tasks/sendSubscribe - Send and subscribe to updates Core Protocol Methods 

{ "jsonrpc": "2.0", "id": "req-001", "method": "message.send", "params": { "message": { "role": "user", "parts": [ { "kind": "text", "text": "Generate an image of a sailboat on the ocean." } ] "messageId": "msg-user-001" } } } Task Followup { "jsonrpc": "2.0", "id": "req-001", "result": { "id": "task-boat-gen-123", "contextId": "ctx-conversation-abc", "status": { "state": "completed" }, "artifacts": [ { "artifactId": "artifact-boat-v1-xyz", "name": "sailboat_image.png", "description": "A generated image of a sailboat on the ocean.", "parts": [ { "kind": "file", "file": { "name": "sailboat_image.png", "mimeType": "image/png", "bytes": "base64_encoded_png_data_of_a_sailboat" } } ] } ], { "jsonrpc": "2.0", "id": "req-002", "method": "message.send", "params": { "message": { "role": "user", "messageId": "msg-user-002", "contextId": "ctx-conversation-abc", "referenceTaskIds": [ "task-boat-gen-123" ], "parts": [ { "kind": "text", "text": "Please modify the sailboat to be red." } ] } } } { "jsonrpc": "2.0", "id": "req-002", "result": { "id": "task-boat-color-456", "contextId": "ctx-conversation-abc", "status": { "state": "completed" }, "artifacts": [ { "artifactId": "artifact-boat-v2-red-pqr", "name": "sailboat_image.png", "description": "A generated image of a red sailboat on the oce "parts": [ { "kind": "file", "file": { "name": "sailboat_image.png", "mimeType": "image/png", "bytes": "base64_encoded_png_data_of_a_RED_sailboat" } } ] } ], "kind": "task" } } 

A2A Agentic Applications https://a2a-protocol.org/latest/topics/a2a-and-mcp/#a2a-mcp-complementary-protocols-for-agentic-systems 

Key Takeaways • Open standard for agent interoperability • Built on existing web standards • Enterprise-grade security built-in • Complements MCP for complete stack Agent-to-Agent Protocol (A2A) Of fi cial Resources a2a-protocol.org github.com/a2aproject/A2A https://github.com/a2aproject/a2a- inspector https://www.a2aprotocol.net/docs/ speci fi cation 

The Full Protocol Stack Model Context Protocol (MCP) The Agent–User Interaction (AG-UI) Protocol Agent-to-Agent Protocol (A2A) 

The Agent–User Interaction (AG-UI) Protocol AG-UI is an open, lightweight, event-based protocol that standardizes how AI agents connect to user-facing applications. https://docs.ag-ui.com/introduction 

• MCP connects agents to tools & context • A2A enables agent-to-agent communication • No standard for agent-to-user interaction • Each framework invented custom protocols Missing Link 

Traditional APIs Don't Work for Agents Agentic applications break the request/response model. Client makes request → server returns data → interaction ends. Agents don't work this way. 

• Custom WebSocket formats per agent • Ad-hoc JSON parsing and text hacks • Reinvent adapters for each framework • Complex state synchronization WITHOUT AG-UI (PAIN POINTS) 

Standardisations Without AG-UI With AG-UI Framework fragmentation Every UI must code adapters for LangGraph, CrewAI, Mastra, etc. (M×N problem) Single protocol; any framework works with any UI (M+N) State synchronization Manual polling or complex WebSocket logic JSON Patch state deltas, standardized sync Human-in-the-loop Custom approval workflows per app Standardized HITL events built into protocol Debugging Server-side logs only; UI-agent communication is a black box Full client-side event tracing, transparent execution Generative UI No standard for agents to specify UI components Built-in component rendering events 

Ecosystem Pydantic AI 

AG-UI Server https://ai.pydantic.dev/ui/ag-ui/#examples https://docs.copilotkit.ai/pydantic-ai/quickstart/pydantic-ai?path=exiting-agent • Major framework support • "Simple" one-line expose • Fine grained control possible 

CopilotKit Framework • Manages Communication • Helps with state • Human in the loop (HITL) • Use ready react components AG-UI Client https://docs.copilotkit.ai/pydantic-ai/quickstart/pydantic-ai?path=exiting-agent 

Server Communication Events Category Description Lifecycle Events Monitor the progression of agent runs Text Message Events Handle streaming textual content Tool Call Events Manage tool executions by agents State Management Events Synchronize state between agents and UI Activity Events Represent ongoing activity progress Special Events Support custom functionality Draft Events Proposed events under development https://docs.ag-ui.com/concepts/events ➡ ∑16 standard events 

• SSE (Server-Sent Events) - Default, text-based, HTTP • Binary Protocol - High performance, custom serialization • WebSocket - Bidirectional, low latency • HTTP Polling - Fallback for restrictive networks Communication Transport 

1. TEXT_MESSAGE_START { messageId, role: "assistant" } 2. TEXT_MESSAGE_CONTENT (×N) { messageId, delta: "Hello" } { messageId, delta: " world" } 3. TEXT_MESSAGE_END { messageId } Text / Tool Streaming Event Pattern 1. TOOL_CALL_START { toolCallId: "call_123", toolName: "search_database" } 2. TOOL_CALL_ARGS { toolCallId: "call_123", args: { query: "users" } } 3. TOOL_CALL_END { toolCallId: "call_123", result: [...] } 

• Bi-directional state management • STATE_SNAPSHOT Complete state object for initialization or refresh • STATE_DELTA JSON Patch (RFC 6902) for ef fi cient incremental updates State 

Static • Agent speci fi es exact component and props to render • E.g. Component is mapped to a speci fi c event in the UI UI Capbilities Declarative • Agent describes intent, framework selects components • Agent knows about components and props 

• Simple request/response with no streaming • Batch processing without user interaction • Static content delivery • Ultra-low latency requirements (<10ms) No-Usecase 

• Real-time Streaming Complexity • Tool Orchestration • Agents call functions, run code, hit APIs — UI must show progress and handle approval • Concurrency & Cancellation • Uni fi ed Interface: LangChain, CrewAI, Mastra all speak different dialects Solved Problems 

• Keep Humans in the loop • Visual Feedback • Actual questions and commits • Increase acceptance through observability • Loading placeholder effect AG-UI 

• Documentation: docs.ag-ui.com • GitHub: github.com/ag-ui-protocol/ag-ui • AG-UI Dojo: https://dojo.ag-ui.com/pydantic-ai/ AG-UI Ressources 

It's a wrap! • Slides: https://thinktecture.com/max-marschall • Contact: @MaxOSchulte, [email protected]