Guide

How to find and fix failures in multi-agent systems

Single-agent evals miss handoff failures. When Agent A passes bad context to Agent B, both look fine individually. You need conversation-level tracing that attributes failures to the right node.

Why multi-agent failures are hard to debug

In a single-agent system, the agent that produced the bad output is the agent that caused the problem. In multi-agent systems, that's often wrong. The agent producing the bad output may be responding correctly to bad input from an upstream agent.

End-to-end evaluation says “the conversation failed.” Per-agent evaluation says each agent did fine individually. Neither tells you where the actual problem is.

Four failure modes in multi-agent systems

Each mode requires a different diagnostic approach and a different fix.

Context loss at handoffs

Agent A collects important information from the user. When it hands off to Agent B, some or all of that context is lost. Agent B asks the user to repeat themselves or proceeds without critical information.

A triage agent correctly identifies the user's account type and issue. The specialist agent it routes to doesn't receive the account type and starts from scratch.

Wrong agent attribution

The end-to-end conversation fails, but it's unclear which agent caused the failure. Agent B gives a bad response - but only because Agent A passed it incorrect context. Blaming Agent B leads to fixing the wrong thing.

A routing agent misclassifies a billing question as a technical issue. The technical support agent can't help. The team 'fixes' the technical agent instead of the router.

Cascading failures

A small error in one agent compounds through the chain. Each subsequent agent makes reasonable decisions based on bad input, but the end result is completely wrong.

Agent A slightly misinterprets the user's intent. Agent B builds on that interpretation. Agent C acts on it. By the final response, the original intent is unrecoverable.

Duplicate or contradictory actions

Multiple agents act on the same request without coordination. One agent resolves the issue while another escalates it. Or two agents give the user conflicting information.

A refund agent processes a partial refund while an escalation agent creates a ticket for a full refund review. The customer gets both - partial refund now and a confusing follow-up.

Single-agent evals vs. multi-agent attribution

Single-agent evalMulti-agent attribution
What gets scoredFinal output onlyEach agent's contribution independently
Failure attribution"The agent failed""Agent A's context handoff failed at turn 3"
Handoff qualityNot measuredScored for completeness and accuracy
Root causeOften misattributed to the last agent in the chainTraced to the originating agent
Fix targetThe agent that produced the bad outputThe agent that caused the bad output - which may be different

How multi-agent attribution works

Trace the full conversation across agents

Every agent's contribution is recorded - including the handoff payloads between agents. Each turn is tagged with which agent handled it.

Score each agent independently

Each agent is scored on its own performance - including handoff quality. Did it pass complete context? Did it route correctly? Did it handle the task given its input?

Trace failures upstream

When a downstream agent fails, the system checks: did it fail because of its own behavior, or because of bad input from upstream? Attribution goes to the originating agent.

Fix the right agent, test the full chain

The fix targets the agent that actually caused the failure. Testing runs the full multi-agent flow to catch cascading effects before deployment.

Frequently asked questions

Why do single-agent evals fail for multi-agent systems?

Single-agent evals grade the final output. In a multi-agent system, the final output is the result of a chain of agent interactions. When the output is wrong, single-agent evals can't tell you which agent in the chain caused the failure. Worse, they often attribute the failure to the last agent - which is usually the one that produced the output, not the one that caused the problem.

What is agent-to-agent context loss?

Context loss happens when information collected or generated by one agent doesn't fully transfer to the next agent in the chain. This can be explicit (the handoff payload doesn't include all relevant fields) or implicit (the receiving agent doesn't interpret the context correctly). It's the most common failure mode in multi-agent systems and the hardest to detect with end-to-end evaluation.

How do you attribute failures to the right agent?

Conversation-level tracing scores each agent's contribution independently - including the quality of handoffs between agents. When a downstream agent fails, the system traces back through the chain to determine whether the failure originated in the downstream agent's behavior or in the context it received. This prevents fixing the wrong agent.

Can you test multi-agent interactions in simulation?

Yes. Simulation testing replays the full multi-agent flow with synthetic personas, including handoffs between agents. This lets you test changes to one agent's behavior and see how it affects the entire chain - catching cascading effects that single-agent testing misses.

How do you fix a handoff failure between agents?

First, diagnose whether the handoff failure is a context completeness issue (information not passed) or a context interpretation issue (information passed but misunderstood). Then generate a targeted fix - either to the sending agent's handoff format or the receiving agent's context processing. The fix is simulation-tested across the full chain and production-verified.

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