Feed Validation Errors Back to LLMs to Fix Structured Output Failures

When an LLM returns structured output that fails schema validation, a plain retry offers little improvement since it repeats the same prompt under similar conditions. A more effective approach involves passing the validation error and the model's previous flawed response back into the next prompt, prompting the model to edit rather than regenerate. This technique was applied in a RAG platform, where a retry loop formats the validation exception into plain-language instructions and supplies the prior output as the object to correct. The method typically preserves already-correct fields while fixing only the specific field that failed, improving success rates significantly. Key caveats include capping retry attempts to control costs and ensuring a fallback for cases where the original response is too malformed to serialize back into the prompt.