{"record":{"id":"6748893663b0303c","repo":"microsoft/autogen","slug":"agent-fails-to-generate-json-response","errorCode":null,"errorMessage":"agent fails to generate json response","messagePattern":"agent fails to generate json response","errorType":"exception","errorClass":"Exception","httpStatus":null,"severity":"error","filePath":"dotnet/samples/AgentChat/AutoGen.Basic.Sample/CodeSnippet/MiddlewareAgentCodeSnippet.cs","lineNumber":173,"sourceCode":"            {\n                if (JsonSerializer.Deserialize<Dictionary<string, object>>(reply.GetContent()) is { } dict)\n                {\n                    return reply;\n                }\n                else\n                {\n                    await Task.Delay(1000);\n                    var reviewPrompt = @\"The format is not json, please modify your response to json format\n        -- ORIGINAL MESSAGE --\n        {reply.Content}\n        -- END OF ORIGINAL MESSAGE --\n        \n        Reply again with json format.\";\n                    reply = await agent.SendAsync(reviewPrompt, messages, ct);\n                }\n            }\n\n            throw new Exception(\"agent fails to generate json response\");\n        });\n        #endregion code_snippet_response_format_forcement\n    }\n}\n","sourceCodeStart":155,"sourceCodeEnd":178,"githubUrl":"https://github.com/microsoft/autogen/blob/027ecf0a379bcc1d09956d46d12d44a3ad9cee14/dotnet/samples/AgentChat/AutoGen.Basic.Sample/CodeSnippet/MiddlewareAgentCodeSnippet.cs#L155-L178","documentation":"Thrown by a custom middleware in MiddlewareAgentCodeSnippet that enforces JSON-formatted replies: after up to two attempts (original prompt plus a 'reply again in json' review prompt), the reply still wasn't valid JSON, so the middleware gives up and throws. It demonstrates a response-format enforcement pattern where failure to comply is a hard error, not a retry-forever loop.","triggerScenarios":"Calling the wrapped agent where the LLM repeatedly returns prose/markdown instead of pure JSON — e.g. wrapping JSON in ```json fences, adding commentary, or the model being too weak to follow the format instruction. The retry loop is bounded, so a persistently non-compliant model exhausts it.","commonSituations":"Using a small model that ignores JSON format instructions; prompt competing with other instructions ('explain your answer'); JSON content containing characters the model escapes incorrectly; max-token truncation cutting the JSON mid-stream.","solutions":["Catch the exception at the caller and re-ask with an even more explicit instruction (provide a schema/example in the prompt).","Switch to a model that supports native structured/JSON output (e.g. response_format json_object / json_schema) instead of prompt-based enforcement.","Strip markdown fences before parsing: reply.Content.replace(/^```(json)?|```$/g, '').","Increase max_tokens so the JSON response isn't truncated."],"exampleFix":"// before\nreply = await agent.SendAsync(reviewPrompt, messages, ct);\n// (loop ends, still not json)\nthrow new Exception(\"agent fails to generate json response\");\n\n// after (tolerant parse before giving up)\nvar content = (reply.Content ?? \"\").Trim()\n    .Replace(\"```json\", \"\").Replace(\"```\", \"\").Trim();\ntry { JsonDocument.Parse(content); return reply; }\ncatch { throw new Exception(\"agent fails to generate json response\"); }","handlingStrategy":"try-catch","validationCode":"bool IsJson(string? s)\n{\n    if (string.IsNullOrWhiteSpace(s)) return false;\n    try { System.Text.Json.JsonDocument.Parse(s!); return true; }\n    catch { return false; }\n}","typeGuard":null,"tryCatchPattern":"try\n{\n    reply = await jsonEnforcingAgent.SendAsync(prompt, ct: ct);\n}\ncatch (Exception e) when (e.Message.Contains(\"agent fails to generate json response\"))\n{\n    // Bounded retries are exhausted: degrade to a non-JSON path or re-prompt the user\n    reply = await fallbackPlainAgent.SendAsync(prompt, ct: ct);\n}","preventionTips":["Prefer native JSON/structured output modes over prompt-based enforcement.","Strip markdown code fences before parsing model output.","Always catch this exception; the middleware deliberately fails hard after its retry budget."],"tags":["llm","json","dotnet","middleware","sample"],"backgroundTag":null,"analyzedSha":"027ecf0a379bcc1d09956d46d12d44a3ad9cee14","analyzedAt":"2026-08-15T03:38:00.719Z","schemaVersion":2},"datasetVersion":"2026-08-15T17:31:12.345Z"}