diff --git a/frontend/src/services/toolRegistry.ts b/frontend/src/services/toolRegistry.ts
index 08d0ea4..6c5db89 100644
--- a/frontend/src/services/toolRegistry.ts
+++ b/frontend/src/services/toolRegistry.ts
@@ -76,8 +76,13 @@ function internalClearAllTools() {
   for (const name of registeredToolsSet) {
     webmcpInstance.unregisterTool(name)
   }
+  // Clear session storage to prevent stale schemas
+  if (typeof webmcpInstance._clearStoredItems === 'function') {
+    webmcpInstance._clearStoredItems()
+  }
   console.log(`[ToolRegistry] Cleared ${registeredToolsSet.size} tools`)
   registeredToolsSet.clear()
+  toolConfigsCache = null
 }
 
 // Tool configurations cache
diff --git a/frontend/src/services/tools/handlers/canvasHandlers.ts b/frontend/src/services/tools/handlers/canvasHandlers.ts
index 4f51b50..9bb1b6a 100644
--- a/frontend/src/services/tools/handlers/canvasHandlers.ts
+++ b/frontend/src/services/tools/handlers/canvasHandlers.ts
@@ -477,43 +477,50 @@ export function createCanvasHandlers(): ToolConfig[] {
         if (!container) return 'Error: canvas no encontrado'
 
         const attr = args.attribute || 'innerHTML'
-        const elements = args.all
-          ? Array.from(container.querySelectorAll(args.selector))
-          : [container.querySelector(args.selector)].filter(Boolean) as Element[]
+        const allElements = Array.from(container.querySelectorAll(args.selector))
 
-        if (elements.length === 0) {
+        if (allElements.length === 0) {
           return `Error: no match ${args.selector}`
         }
 
+        // Find which elements contain old_value
+        const matchingElements = args.old_value
+          ? allElements.filter(el => {
+              const current = attr === 'style' ? (el as HTMLElement).style.cssText : (el as any)[attr]
+              return current && current.includes(args.old_value!)
+            })
+          : allElements
+
+        if (args.old_value && matchingElements.length === 0) {
+          return `Error: old_value not found`
+        }
+
+        if (!args.all && matchingElements.length > 1) {
+          return `Error: ${matchingElements.length} matches found. Use all:true or narrow selector.`
+        }
+
+        const elements = args.all ? matchingElements : [matchingElements[0]]
         let editedCount = 0
+
         for (const el of elements) {
           const htmlEl = el as HTMLElement
 
           if (args.old_value) {
-            // Modo Edit: buscar y reemplazar
             const current = attr === 'style' ? htmlEl.style.cssText : (htmlEl as any)[attr]
-            if (current && current.includes(args.old_value)) {
-              const newVal = current.replace(args.old_value, args.new_value)
-              if (attr === 'style') {
-                htmlEl.style.cssText = newVal
-              } else {
-                (htmlEl as any)[attr] = newVal
-              }
-              editedCount++
+            const newVal = current.replace(args.old_value, args.new_value)
+            if (attr === 'style') {
+              htmlEl.style.cssText = newVal
+            } else {
+              (htmlEl as any)[attr] = newVal
             }
           } else {
-            // Modo Write: reemplazar todo
             if (attr === 'style') {
               htmlEl.style.cssText = args.new_value
             } else {
               (htmlEl as any)[attr] = args.new_value
             }
-            editedCount++
           }
-        }
-
-        if (editedCount === 0) {
-          return `Error: old_value not found`
+          editedCount++
         }
 
         return `OK ${editedCount} edited`
@@ -534,9 +541,9 @@ export function createCanvasHandlers(): ToolConfig[] {
             description: 'inject (default), replace, remove'
           }
         },
-        required: ['css']
+        required: []
       },
-      handler: (args: { css: string; id?: string; mode?: string }) => {
+      handler: (args: { css?: string; id?: string; mode?: string }) => {
         const mode = args.mode || 'inject'
         const styleId = args.id ? `canvas-css-${args.id}` : `canvas-css-${Date.now()}`
 
@@ -550,6 +557,8 @@ export function createCanvasHandlers(): ToolConfig[] {
           return `Error: css:${args.id} not found`
         }
 
+        if (!args.css) return 'Error: css required for inject/replace'
+
         let styleEl = args.id ? document.getElementById(`canvas-css-${args.id}`) : null
 
         if (mode === 'replace' && styleEl) {
diff --git a/frontend/src/services/webmcp.ts b/frontend/src/services/webmcp.ts
index 987f120..3a2e6d3 100644
--- a/frontend/src/services/webmcp.ts
+++ b/frontend/src/services/webmcp.ts
@@ -193,6 +193,10 @@ export function clearAllTools() {
   }
   console.log(`[WebMCP] Cleared ${registeredTools.size} tools`)
   registeredTools.clear()
+  // Clear session storage to prevent stale schemas on reconnect
+  if (typeof webmcpInstance._clearStoredItems === 'function') {
+    webmcpInstance._clearStoredItems()
+  }
 }
 
 /**