Diagnosing Agent Errors: Check These Four Layers First
Hot-Leadership-6431 · reddit · 2026-07-13
The author suggests that when an agent provides a wrong answer, don't immediately tweak the prompt. Instead, localize the issue layer by layer.
The troubleshooting order is: 1) Check if the input was actually passed to the model, focusing on the final string rather than the template; 2) Check if the required facts are actually present in the retrieval/context by inspecting the recalled chunks; 3) Verify if the tool call parameters are correct and the tool returns as expected; 4) Only after confirming the first three layers are normal should the issue be attributed to the prompt or model reasoning.
They share an example where an agent kept fabricating order numbers. Initially, it seemed necessary to add "do not make things up" to the prompt, but the actual problem was that the retrieval failed to fetch the data, and the lookup tool passed the customer name into the order number field. The post concludes with a reminder to toggle these debug logs only for failed cases, as leaving them on in production would incur excessive debugging costs.
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