How to Build Multi-Agent AI Systems That Actually Handoff Correctly

Most multi-agent systems fail not because the AI is dumb—but because the handoffs are broken. I've built 8+ production AI agents, and the single hardest problem isn't prompts, isn't tools, it's handoff reliability. When Agent A finishes its task and passes to Agent B, something almost always goes wrong: lost context, wrong format, incomplete state. Here's the architecture that fixed it for me. The Problem Agent A: "Done! Here's the result." Agent B: "Wait, what format is this? Where's the metadata?" Classic. The output format Agent A thinks is clear becomes a mystery to Agent B. The Fix: Structured Handoff Protocol Instead of freeform text, every handoff follows this structure: interface Handoff { source: AgentType; target: AgentType; payload: any; metadata: { confidence: number; // 0-1, how sure is the source? completeness: number; // 0-1, did we get everything? notes: string; // Anything worth noting? }; requirements: string[]; // What does the target need to know? } Why This Works C