What it covers

Observability in agent systems means capturing structured records of the agent's internal decisions and external actions. That includes spans for each reasoning step, tool-call records showing what was requested and what came back, token usage per step, latency measurements, error states, and the full context window at each decision point. Unlike simple API logging, agent observability preserves the chain of causation — you can trace backward from a bad output to the specific prompt or tool response that caused it.

Why agents need more than traditional monitoring

Traditional software monitoring catches exceptions and latency. Agents fail in ways that produce no exception: they choose the wrong tool, misinterpret a context window, loop unnecessarily, or produce plausible-sounding but incorrect outputs. These failures are invisible to a health check. Observability gives you the reasoning trace so you can see not just that the agent failed but why it made the choice it did — which is the only way to reliably fix non-deterministic systems.

What to instrument

The minimum instrumentation for an agent system covers four layers: LLM calls (prompt, completion, model, token count, latency), tool calls (tool name, input arguments, output, duration), agent steps (which step in a multi-step plan, transitions between steps), and workflow-level events (task start, end, escalations, human handoffs). Each layer should emit a trace ID that links all events from a single agent run, so you can reconstruct the full execution path in sequence.

When it becomes critical

Observability becomes critical the moment an agent has write access to production systems — because at that point, a reasoning failure is not just a bad answer but a bad action. Before that threshold, it is still useful: it speeds debugging during development and makes prompt regression visible. After that threshold, it is infrastructure. Teams deploying agents to production without observability are operating blind in systems that can take autonomous actions.