Extract structured JSON from messy LLM output, validate against a shape spec, and generate retry prompts via @mukundakatta/agentcast-mcp (npx)

{
  "server": "@mukundakatta/agentcast-mcp",
  "version": "0.1.0",
  "transport": "stdio",
  "entry": "dist/server.js",
  "tools": 3,
  "calls": 18,
  "success_rate": "100%",
  "p50_ms": 0,
  "trace": [
    {
      "tool": "extract_json",
      "args": {
        "text": "Sure! Here is the data:

```json
{"city": "Istanbul", "population": 16000000}
```

Let me know if you need more."
      },
      "result": {
        "value": {
          "city": "Istanbul",
          "population": 16000000
        },
        "found": true,
        "source": "fenced_json"
      },
      "ms": 1
    },
    {
      "tool": "extract_json",
      "args": {
        "text": "Based on my analysis, the answer is {"result": "success", "score": 0.95, "labels": ["positive", "confident"]} and you can use it directly."
      },
      "result": {
        "value": {
          "result": "success",
          "score": 0.95,
          "labels": ["positive", "confident"]
        },
        "found": true,
        "source": "balanced_substring"
      },
      "ms": 0
    },
    {
      "tool": "extract_json",
      "args": {
        "text": "I am sorry, I cannot provide that information. Please try again."
      },
      "result": {
        "value": null,
        "found": false,
        "source": "none"
      },
      "ms": 1
    },
    {
      "tool": "validate_response",
      "args": {
        "value": {
          "name": "Alice",
          "age": 30,
          "active": true
        },
        "shape": {
          "name": "string",
          "age": "number",
          "active": "boolean"
        }
      },
      "result": {
        "valid": true
      },
      "ms": 1
    },
    {
      "tool": "validate_response",
      "args": {
        "value": {
          "name": "Alice"
        },
        "shape": {
          "name": "string",
          "age": "number"
        }
      },
      "result": {
        "valid": false,
        "error": "missing required field 'age'"
      },
      "ms": 0
    },
    {
      "tool": "validate_response",
      "args": {
        "value": {
          "name": "Alice",
          "age": "thirty"
        },
        "shape": {
          "name": "string",
          "age": "number"
        }
      },
      "result": {
        "valid": false,
        "error": "field 'age' should be number, got string"
      },
      "ms": 0
    },
    {
      "tool": "build_retry_prompt",
      "args": {
        "attempts": [
          {
            "text": "The answer is: name is Alice and age is 30.",
            "error": "Expected JSON object with {name: string, age: number}, got plain text."
          }
        ],
        "expected_shape": {
          "name": "string",
          "age": "number"
        }
      },
      "result": {
        "feedback": "Your previous response did not match the required shape. Error: Expected JSON object with {name: string, age: number}, got plain text.

Try again. Respond with ONLY valid JSON that fixes the error above.

Expected shape: {"name":"string","age":"number"}"
      },
      "ms": 0
    },
    {
      "tool": "pipeline",
      "extract": {
        "value": {
          "product": "Widget",
          "price": "19.99"
        },
        "source": "fenced_json"
      },
      "validate": {
        "valid": false,
        "error": "field 'price' should be number, got string"
      },
      "retry": {
        "feedback": "...Respond with ONLY valid JSON...Expected shape: {"product":"string","price":"number"}"
      },
      "ms": 0
    }
  ]
}