Add JSON validation to tool execution

Prevents execution of tools with invalid JSON parameters by validating JSON
syntax before tool execution and showing error UI for invalid input.

- Add validateJson method to DynamicJsonForm via forwardRef
- Add validation check in ToolsTab before tool execution
- Reuse existing JsonEditor error display for consistent UX

client/src/components/DynamicJsonForm.tsx

@@ -1,4 +1,4 @@
-import { useState, useEffect, useCallback, useRef } from "react";
+import { useState, useEffect, useCallback, useRef, forwardRef, useImperativeHandle } from "react";
 import { Button } from "@/components/ui/button";
 import { Input } from "@/components/ui/input";
 import JsonEditor from "./JsonEditor";
@@ -13,6 +13,10 @@ interface DynamicJsonFormProps {
   maxDepth?: number;
 }
 
+export interface DynamicJsonFormRef {
+  validateJson: () => { isValid: boolean; error: string | null };
+}
+
 const isSimpleObject = (schema: JsonSchemaType): boolean => {
   const supportedTypes = ["string", "number", "integer", "boolean", "null"];
   if (supportedTypes.includes(schema.type)) return true;
@@ -22,12 +26,12 @@ const isSimpleObject = (schema: JsonSchemaType): boolean => {
   );
 };
 
-const DynamicJsonForm = ({
+const DynamicJsonForm = forwardRef<DynamicJsonFormRef, DynamicJsonFormProps>(({
   schema,
   value,
   onChange,
   maxDepth = 3,
-}: DynamicJsonFormProps) => {
+}, ref) => {
   const isOnlyJSON = !isSimpleObject(schema);
   const [isJsonMode, setIsJsonMode] = useState(isOnlyJSON);
   const [jsonError, setJsonError] = useState<string>();
@@ -108,6 +112,25 @@ const DynamicJsonForm = ({
     }
   };
 
+  const validateJson = () => {
+    if (!isJsonMode) return { isValid: true, error: null };
+    try {
+      const jsonStr = rawJsonValue.trim();
+      if (!jsonStr) return { isValid: true, error: null };
+      JSON.parse(jsonStr);
+      setJsonError(undefined);
+      return { isValid: true, error: null };
+    } catch (err) {
+      const errorMessage = err instanceof Error ? err.message : "Invalid JSON";
+      setJsonError(errorMessage);
+      return { isValid: false, error: errorMessage };
+    }
+  };
+
+  useImperativeHandle(ref, () => ({
+    validateJson,
+  }));
+
   const renderFormFields = (
     propSchema: JsonSchemaType,
     currentValue: JsonValue,
@@ -303,6 +326,6 @@ const DynamicJsonForm = ({
       )}
     </div>
   );
-};
+});
 
 export default DynamicJsonForm;

client/src/components/ToolsTab.tsx

@@ -1,11 +1,11 @@
-import { Alert, AlertDescription } from "@/components/ui/alert";
+import { Alert, AlertDescription, AlertTitle } from "@/components/ui/alert";
 import { Button } from "@/components/ui/button";
 import { Checkbox } from "@/components/ui/checkbox";
 import { Input } from "@/components/ui/input";
 import { Label } from "@/components/ui/label";
 import { TabsContent } from "@/components/ui/tabs";
 import { Textarea } from "@/components/ui/textarea";
-import DynamicJsonForm from "./DynamicJsonForm";
+import DynamicJsonForm, { DynamicJsonFormRef } from "./DynamicJsonForm";
 import type { JsonValue, JsonSchemaType } from "@/utils/jsonUtils";
 import { generateDefaultValue } from "@/utils/schemaUtils";
 import {
@@ -13,8 +13,8 @@ import {
   ListToolsResult,
   Tool,
 } from "@modelcontextprotocol/sdk/types.js";
-import { Loader2, Send, ChevronDown, ChevronUp } from "lucide-react";
+import { Loader2, Send, ChevronDown, ChevronUp, AlertCircle } from "lucide-react";
-import { useEffect, useState } from "react";
+import { useEffect, useState, useRef } from "react";
 import ListPane from "./ListPane";
 import JsonView from "./JsonView";
 import ToolResults from "./ToolResults";
@@ -28,6 +28,7 @@ const ToolsTab = ({
   setSelectedTool,
   toolResult,
   nextCursor,
+  error,
 }: {
   tools: Tool[];
   listTools: () => void;
@@ -42,6 +43,7 @@ const ToolsTab = ({
   const [params, setParams] = useState<Record<string, unknown>>({});
   const [isToolRunning, setIsToolRunning] = useState(false);
   const [isOutputSchemaExpanded, setIsOutputSchemaExpanded] = useState(false);
+  const formRefs = useRef<Record<string, DynamicJsonFormRef | null>>({});
 
   useEffect(() => {
     const params = Object.entries(
@@ -84,7 +86,13 @@ const ToolsTab = ({
             </h3>
           </div>
           <div className="p-4">
-            {selectedTool ? (
+            {error ? (
+              <Alert variant="destructive">
+                <AlertCircle className="h-4 w-4" />
+                <AlertTitle>Error</AlertTitle>
+                <AlertDescription>{error}</AlertDescription>
+              </Alert>
+            ) : selectedTool ? (
               <div className="space-y-4">
                 <p className="text-sm text-gray-600 dark:text-gray-400">
                   {selectedTool.description}
@@ -137,6 +145,7 @@ const ToolsTab = ({
                         ) : prop.type === "object" || prop.type === "array" ? (
                           <div className="mt-1">
                             <DynamicJsonForm
+                              ref={(ref) => (formRefs.current[key] = ref)}
                               schema={{
                                 type: prop.type,
                                 properties: prop.properties,
@@ -174,6 +183,7 @@ const ToolsTab = ({
                         ) : (
                           <div className="mt-1">
                             <DynamicJsonForm
+                              ref={(ref) => (formRefs.current[key] = ref)}
                               schema={{
                                 type: prop.type,
                                 properties: prop.properties,
@@ -232,6 +242,12 @@ const ToolsTab = ({
                 )}
                 <Button
                   onClick={async () => {
+                    // Validate JSON inputs before calling tool
+                    const hasValidationErrors = Object.values(formRefs.current).some(
+                      (ref) => ref && !ref.validateJson().isValid
+                    );
+                    if (hasValidationErrors) return;
+
                     try {
                       setIsToolRunning(true);
                       await callTool(selectedTool.name, params);