diff --git a/packages/ui/src/App.tsx b/packages/ui/src/App.tsx
index ea314e15..7df5b893 100644
--- a/packages/ui/src/App.tsx
+++ b/packages/ui/src/App.tsx
@@ -1,7 +1,9 @@
 import { Component, Show, createMemo, createEffect, createSignal } from "solid-js"
 import { Dialog } from "@kobalte/core/dialog"
 import { Toaster } from "solid-toast"
+import AlertDialog from "./components/alert-dialog"
 import FolderSelectionView from "./components/folder-selection-view"
+import { showConfirmDialog } from "./stores/alerts"
 import InstanceTabs from "./components/instance-tabs"
 import InstanceDisconnectedModal from "./components/instance-disconnected-modal"
 import InstanceShell from "./components/instance/instance-shell"
@@ -135,11 +137,21 @@ const App: Component = () => {
   }
 
   async function handleCloseInstance(instanceId: string) {
-    if (confirm("Stop OpenCode instance? This will stop the server.")) {
-      await stopInstance(instanceId)
-      if (instances().size === 0) {
-        setHasInstances(false)
-      }
+    const confirmed = await showConfirmDialog(
+      "Stop OpenCode instance? This will stop the server.",
+      {
+        title: "Stop instance",
+        variant: "warning",
+        confirmLabel: "Stop",
+        cancelLabel: "Keep running",
+      },
+    )
+
+    if (!confirmed) return
+
+    await stopInstance(instanceId)
+    if (instances().size === 0) {
+      setHasInstances(false)
     }
   }
 
@@ -321,6 +333,8 @@ const App: Component = () => {
           </div>
         </Show>
 
+        <AlertDialog />
+
         <Toaster
           position="top-right"
           gutter={16}
diff --git a/packages/ui/src/components/alert-dialog.tsx b/packages/ui/src/components/alert-dialog.tsx
new file mode 100644
index 00000000..6fb39b19
--- /dev/null
+++ b/packages/ui/src/components/alert-dialog.tsx
@@ -0,0 +1,132 @@
+import { Dialog } from "@kobalte/core/dialog"
+import { Component, Show, createEffect } from "solid-js"
+import { alertDialogState, dismissAlertDialog } from "../stores/alerts"
+import type { AlertVariant, AlertDialogState } from "../stores/alerts"
+
+const variantAccent: Record<AlertVariant, { badgeBg: string; badgeBorder: string; badgeText: string; symbol: string; fallbackTitle: string }> = {
+  info: {
+    badgeBg: "var(--badge-neutral-bg)",
+    badgeBorder: "var(--border-base)",
+    badgeText: "var(--accent-primary)",
+    symbol: "i",
+    fallbackTitle: "Heads up",
+  },
+  warning: {
+    badgeBg: "rgba(255, 152, 0, 0.14)",
+    badgeBorder: "var(--status-warning)",
+    badgeText: "var(--status-warning)",
+    symbol: "!",
+    fallbackTitle: "Please review",
+  },
+  error: {
+    badgeBg: "var(--danger-soft-bg)",
+    badgeBorder: "var(--status-error)",
+    badgeText: "var(--status-error)",
+    symbol: "!",
+    fallbackTitle: "Something went wrong",
+  },
+}
+
+function dismiss(confirmed: boolean, payload?: AlertDialogState | null) {
+  const current = payload ?? alertDialogState()
+  if (current?.type === "confirm") {
+    if (confirmed) {
+      current.onConfirm?.()
+    } else {
+      current.onCancel?.()
+    }
+    current.resolve?.(confirmed)
+  } else if (confirmed) {
+    current?.onConfirm?.()
+  }
+  dismissAlertDialog()
+}
+
+const AlertDialog: Component = () => {
+  let primaryButtonRef: HTMLButtonElement | undefined
+
+  createEffect(() => {
+    if (alertDialogState()) {
+      queueMicrotask(() => {
+        primaryButtonRef?.focus()
+      })
+    }
+  })
+
+  return (
+    <Show when={alertDialogState()} keyed>
+      {(payload) => {
+        const variant = payload.variant ?? "info"
+        const accent = variantAccent[variant]
+        const title = payload.title || accent.fallbackTitle
+        const isConfirm = payload.type === "confirm"
+        const confirmLabel = payload.confirmLabel || (isConfirm ? "Confirm" : "OK")
+        const cancelLabel = payload.cancelLabel || "Cancel"
+
+        return (
+          <Dialog
+            open
+            modal
+            onOpenChange={(open) => {
+              if (!open) {
+                dismiss(false, payload)
+              }
+            }}
+          >
+            <Dialog.Portal>
+              <Dialog.Overlay class="modal-overlay" />
+              <div class="fixed inset-0 z-50 flex items-center justify-center p-4">
+                <Dialog.Content class="modal-surface w-full max-w-sm p-6 border border-base shadow-2xl" tabIndex={-1}>
+                  <div class="flex items-start gap-3">
+                    <div
+                      class="flex h-12 w-12 shrink-0 items-center justify-center rounded-xl border text-base font-semibold"
+                      style={{
+                        "background-color": accent.badgeBg,
+                        "border-color": accent.badgeBorder,
+                        color: accent.badgeText,
+                      }}
+                      aria-hidden
+                    >
+                      {accent.symbol}
+                    </div>
+                    <div class="flex-1">
+                      <Dialog.Title class="text-lg font-semibold text-primary">{title}</Dialog.Title>
+                      <Dialog.Description class="text-sm text-secondary mt-1 whitespace-pre-line">
+                        {payload.message}
+                        {payload.detail && <p class="mt-2 text-secondary">{payload.detail}</p>}
+                      </Dialog.Description>
+                    </div>
+                  </div>
+
+                  <div class="mt-6 flex justify-end gap-3">
+                    {isConfirm && (
+                      <button
+                        type="button"
+                        class="button-secondary"
+                        onClick={() => dismiss(false, payload)}
+                      >
+                        {cancelLabel}
+                      </button>
+                    )}
+                    <button
+                      type="button"
+                      class="button-primary"
+                      ref={(el) => {
+                        primaryButtonRef = el
+                      }}
+                      onClick={() => dismiss(true, payload)}
+                    >
+                      {confirmLabel}
+                    </button>
+                  </div>
+                </Dialog.Content>
+              </div>
+            </Dialog.Portal>
+          </Dialog>
+        )
+      }}
+    </Show>
+  )
+}
+
+export default AlertDialog
diff --git a/packages/ui/src/components/prompt-input.tsx b/packages/ui/src/components/prompt-input.tsx
index 47d9621a..e749266d 100644
--- a/packages/ui/src/components/prompt-input.tsx
+++ b/packages/ui/src/components/prompt-input.tsx
@@ -10,6 +10,7 @@ import Kbd from "./kbd"
 import HintRow from "./hint-row"
 import { getActiveInstance } from "../stores/instances"
 import { agents, getSessionDraftPrompt, setSessionDraftPrompt, clearSessionDraftPrompt } from "../stores/sessions"
+import { showAlertDialog } from "../stores/alerts"
 
 interface PromptInputProps {
   instanceId: string
@@ -526,7 +527,11 @@ export default function PromptInput(props: PromptInputProps) {
       }
     } catch (error) {
       console.error("Failed to send message:", error)
-      alert("Failed to send message: " + (error instanceof Error ? error.message : String(error)))
+      showAlertDialog("Failed to send message", {
+        title: "Send failed",
+        detail: error instanceof Error ? error.message : String(error),
+        variant: "error",
+      })
     } finally {
       textareaRef?.focus()
     }
diff --git a/packages/ui/src/components/session/session-view.tsx b/packages/ui/src/components/session/session-view.tsx
index 4f5d5af8..04d35b54 100644
--- a/packages/ui/src/components/session/session-view.tsx
+++ b/packages/ui/src/components/session/session-view.tsx
@@ -6,6 +6,7 @@ import MessageStream from "../message-stream"
 import PromptInput from "../prompt-input"
 import { instances } from "../../stores/instances"
 import { loadMessages, sendMessage, forkSession, isSessionMessagesLoading, setActiveParentSession, setActiveSession, runShellCommand } from "../../stores/sessions"
+import { showAlertDialog } from "../../stores/alerts"
 
 interface SessionViewProps {
   sessionId: string
@@ -73,7 +74,10 @@ export const SessionView: Component<SessionViewProps> = (props) => {
       }
     } catch (error) {
       console.error("Failed to revert:", error)
-      alert("Failed to revert to message")
+      showAlertDialog("Failed to revert to message", {
+        title: "Revert failed",
+        variant: "error",
+      })
     }
   }
 
@@ -106,7 +110,10 @@ export const SessionView: Component<SessionViewProps> = (props) => {
       }
     } catch (error) {
       console.error("Failed to fork session:", error)
-      alert("Failed to fork session")
+      showAlertDialog("Failed to fork session", {
+        title: "Fork failed",
+        variant: "error",
+      })
     }
   }
 
diff --git a/packages/ui/src/lib/command-utils.ts b/packages/ui/src/lib/command-utils.ts
index b964e3bc..535454b5 100644
--- a/packages/ui/src/lib/command-utils.ts
+++ b/packages/ui/src/lib/command-utils.ts
@@ -1,5 +1,6 @@
 import type { Command } from "./commands"
 import type { Command as SDKCommand } from "@opencode-ai/sdk"
+import { showAlertDialog } from "../stores/alerts"
 import { activeSessionId, executeCustomCommand } from "../stores/sessions"
 
 export function commandRequiresArguments(template?: string): boolean {
@@ -33,7 +34,10 @@ export function buildCustomCommandEntries(instanceId: string, commands: SDKComma
     action: async () => {
       const sessionId = activeSessionId().get(instanceId)
       if (!sessionId || sessionId === "info") {
-        alert("Select a session before running a custom command.")
+        showAlertDialog("Select a session before running a custom command.", {
+          title: "Session required",
+          variant: "warning",
+        })
         return
       }
       const args = promptForCommandArguments(cmd)
@@ -44,7 +48,10 @@ export function buildCustomCommandEntries(instanceId: string, commands: SDKComma
         await executeCustomCommand(instanceId, sessionId, cmd.name, args)
       } catch (error) {
         console.error("Failed to run custom command:", error)
-        alert("Failed to run custom command. Check the console for details.")
+        showAlertDialog("Failed to run custom command. Check the console for details.", {
+          title: "Command failed",
+          variant: "error",
+        })
       }
     },
   }))
diff --git a/packages/ui/src/lib/hooks/use-commands.ts b/packages/ui/src/lib/hooks/use-commands.ts
index f8a7d49a..ac023799 100644
--- a/packages/ui/src/lib/hooks/use-commands.ts
+++ b/packages/ui/src/lib/hooks/use-commands.ts
@@ -11,6 +11,7 @@ import {
   setActiveSession,
 } from "../../stores/sessions"
 import { setSessionCompactionState } from "../../stores/session-compaction"
+import { showAlertDialog } from "../../stores/alerts"
 import type { Instance } from "../../types/instance"
 
 export interface UseCommandsOptions {
@@ -207,7 +208,10 @@ export function useCommands(options: UseCommandsOptions) {
           setSessionCompactionState(instance.id, sessionId, false)
           console.error("Failed to compact session:", error)
           const message = error instanceof Error ? error.message : "Failed to compact session"
-          alert(`Compact failed: ${message}`)
+          showAlertDialog(`Compact failed: ${message}`, {
+            title: "Compact failed",
+            variant: "error",
+          })
         }
       },
     })
@@ -256,7 +260,10 @@ export function useCommands(options: UseCommandsOptions) {
         }
 
         if (!messageID) {
-          alert("Nothing to undo")
+          showAlertDialog("Nothing to undo", {
+            title: "No actions to undo",
+            variant: "info",
+          })
           return
         }
 
@@ -282,7 +289,10 @@ export function useCommands(options: UseCommandsOptions) {
           }
         } catch (error) {
           console.error("Failed to revert message:", error)
-          alert("Failed to revert message")
+          showAlertDialog("Failed to revert message", {
+            title: "Undo failed",
+            variant: "error",
+          })
         }
       },
     })
diff --git a/packages/ui/src/stores/alerts.ts b/packages/ui/src/stores/alerts.ts
new file mode 100644
index 00000000..a3c7775b
--- /dev/null
+++ b/packages/ui/src/stores/alerts.ts
@@ -0,0 +1,46 @@
+import { createSignal } from "solid-js"
+
+export type AlertVariant = "info" | "warning" | "error"
+
+export type AlertDialogState = {
+  type?: "alert" | "confirm"
+  title?: string
+  message: string
+  detail?: string
+  variant?: AlertVariant
+  confirmLabel?: string
+  cancelLabel?: string
+  onConfirm?: () => void
+  onCancel?: () => void
+  resolve?: (value: boolean) => void
+}
+
+const [alertDialogState, setAlertDialogState] = createSignal<AlertDialogState | null>(null)
+
+export function showAlertDialog(message: string, options?: Omit<AlertDialogState, "message">) {
+  setAlertDialogState({
+    type: "alert",
+    message,
+    ...options,
+  })
+}
+
+export function showConfirmDialog(message: string, options?: Omit<AlertDialogState, "message">): Promise<boolean> {
+  const activeElement = typeof document !== "undefined" ? (document.activeElement as HTMLElement | null) : null
+  activeElement?.blur()
+
+  return new Promise<boolean>((resolve) => {
+    setAlertDialogState({
+      type: "confirm",
+      message,
+      ...options,
+      resolve,
+    })
+  })
+}
+
+export function dismissAlertDialog() {
+  setAlertDialogState(null)
+}
+
+export { alertDialogState }
diff --git a/packages/ui/src/stores/session-events.ts b/packages/ui/src/stores/session-events.ts
index 3b470aba..a123acd0 100644
--- a/packages/ui/src/stores/session-events.ts
+++ b/packages/ui/src/stores/session-events.ts
@@ -16,6 +16,7 @@ import type {
 import { showToastNotification, ToastVariant } from "../lib/notifications"
 import { preferences } from "./preferences"
 import { instances, addPermissionToQueue, removePermissionFromQueue, refreshPermissionsForSession } from "./instances"
+import { showAlertDialog } from "./alerts"
 import {
   sessions,
   setSessions,
@@ -441,7 +442,10 @@ function handleSessionError(_instanceId: string, event: EventSessionError): void
     }
   }
 
-  alert(`Error: ${message}`)
+  showAlertDialog(`Error: ${message}`, {
+    title: "Session error",
+    variant: "error",
+  })
 }
 
 function handleMessageRemoved(instanceId: string, event: MessageRemovedEvent): void {