feat(tools): add getToolExplanation() method with XML examples for LLM tool calling

Each tool now provides comprehensive documentation including parameter
schemas and concrete <tool_call> XML examples. This helps smaller LLMs
understand the exact format required for tool invocation.

ts/smartagent.tools.json.ts

@@ -175,6 +175,37 @@ export class JsonValidatorTool extends BaseToolWrapper {
     }
   }
 
+  public getToolExplanation(): string {
+    return `## Tool: json
+Validate and format JSON data. Use this to verify your JSON output is valid before completing a task.
+
+### Actions:
+
+**validate** - Validate that a string is valid JSON and optionally check required fields
+Parameters:
+  - jsonString (required): The JSON string to validate
+  - requiredFields (optional): Array of field names that must be present
+
+Example:
+<tool_call>
+  <tool>json</tool>
+  <action>validate</action>
+  <params>{"jsonString": "{\\"invoice_number\\":\\"INV-001\\",\\"total\\":99.99}", "requiredFields": ["invoice_number", "total"]}</params>
+</tool_call>
+
+**format** - Parse and pretty-print JSON string
+Parameters:
+  - jsonString (required): The JSON string to format
+
+Example:
+<tool_call>
+  <tool>json</tool>
+  <action>format</action>
+  <params>{"jsonString": "{\\"name\\":\\"test\\",\\"value\\":123}"}</params>
+</tool_call>
+`;
+  }
+
   getCallSummary(action: string, params: Record<string, unknown>): string {
     const jsonStr = (params.jsonString as string) || '';
     const preview = jsonStr.length > 50 ? jsonStr.substring(0, 50) + '...' : jsonStr;