diff --git a/clients/web/src/components/groups/ServerCard/ServerCard.stories.tsx b/clients/web/src/components/groups/ServerCard/ServerCard.stories.tsx
index 74e05e86e8..1a1fbbe5cd 100644
--- a/clients/web/src/components/groups/ServerCard/ServerCard.stories.tsx
+++ b/clients/web/src/components/groups/ServerCard/ServerCard.stories.tsx
@@ -102,6 +102,21 @@ export const ErroredBorder: Story = {
   },
 };
 
+// The failure reason kept on the errored card (#2783), so it is still there
+// after the toast that first reported it auto-closes. A long transport error
+// with a URL in it wraps inside the card rather than running under the border.
+export const ErroredWithReason: Story = {
+  args: {
+    id: "5e4d3c2b-1a0f-4e9d-8c7b-6a5f4e3d2c1b",
+    name: "Legacy SSE Server",
+    config: { type: "sse", url: "https://mcp.example.com/sse" },
+    connection: disconnected,
+    errored: true,
+    errorMessage:
+      'Remote connect failed (500): {"error":"Failed to start transport: Endpoint origin does not match connection origin: http://10.0.0.5:8000"}',
+  },
+};
+
 // The green border flagging the server that just connected (#1682) — the
 // success mirror of ErroredBorder. It persists while connected and clears on
 // disconnect or a new connection attempt.
diff --git a/clients/web/src/components/groups/ServerCard/ServerCard.test.tsx b/clients/web/src/components/groups/ServerCard/ServerCard.test.tsx
index 49d89ff6ff..7d9787f69c 100644
--- a/clients/web/src/components/groups/ServerCard/ServerCard.test.tsx
+++ b/clients/web/src/components/groups/ServerCard/ServerCard.test.tsx
@@ -364,6 +364,54 @@ describe("ServerCard", () => {
     });
   });
 
+  describe("connection-failed reason (#2783)", () => {
+    const reason =
+      "Failed to start transport: Endpoint origin does not match connection origin: http://10.0.0.5:8000";
+
+    it("shows the failure reason on an errored card", () => {
+      renderWithMantine(
+        <ServerCard
+          {...baseProps}
+          connection={disconnected}
+          errored
+          errorMessage={reason}
+        />,
+      );
+      expect(screen.getByRole("alert")).toHaveTextContent(reason);
+    });
+
+    it("shows the failure reason in compact mode too", () => {
+      renderWithMantine(
+        <ServerCard
+          {...baseProps}
+          connection={disconnected}
+          compact
+          errored
+          errorMessage={reason}
+        />,
+      );
+      expect(screen.getByRole("alert")).toHaveTextContent(reason);
+    });
+
+    it("hides a stale reason once the card is no longer errored", () => {
+      renderWithMantine(
+        <ServerCard
+          {...baseProps}
+          connection={disconnected}
+          errorMessage={reason}
+        />,
+      );
+      expect(screen.queryByRole("alert")).toBeNull();
+    });
+
+    it("renders no reason line for an errored card without a message", () => {
+      renderWithMantine(
+        <ServerCard {...baseProps} connection={disconnected} errored />,
+      );
+      expect(screen.queryByRole("alert")).toBeNull();
+    });
+  });
+
   describe("connection-failed border (#1621)", () => {
     it("draws the red errored-variant border when errored", () => {
       const { container } = renderWithMantine(
diff --git a/clients/web/src/components/groups/ServerCard/ServerCard.tsx b/clients/web/src/components/groups/ServerCard/ServerCard.tsx
index ef62e272ef..8eac0dd472 100644
--- a/clients/web/src/components/groups/ServerCard/ServerCard.tsx
+++ b/clients/web/src/components/groups/ServerCard/ServerCard.tsx
@@ -45,6 +45,12 @@ export interface ServerCardProps extends ServerEntry {
    * is connected or a new connection is attempted.
    */
   errored?: boolean;
+  /**
+   * Why the last connection attempt failed, shown under the header while
+   * `errored` is set (#2783). The failure toast auto-closes after a few
+   * seconds, which left a bare "Failed" with no reason once it had gone.
+   */
+  errorMessage?: string;
   /**
    * When true, this server just connected successfully: the card draws the green
    * highlight border and scrolls itself into view once the monitoring sidebar
@@ -108,6 +114,11 @@ const ProtocolText = Text.withProps({
   ml: "auto",
 });
 
+const ConnectErrorText = Text.withProps({
+  variant: "connectError",
+  role: "alert",
+});
+
 const SubtleButton = Button.withProps({
   variant: "subtle",
   size: "xs",
@@ -173,6 +184,7 @@ export function ServerCard({
   dragHandle,
   highlighted = false,
   errored = false,
+  errorMessage,
   justConnected = false,
   scrollOnHighlight = true,
   onClearHighlight,
@@ -269,6 +281,12 @@ export function ServerCard({
           </HeaderRight>
         </HeaderRow>
 
+        {/* Shown in compact mode too: the reason is the one thing a failed card
+            has to say, and compact hides everything else below the header. */}
+        {errored && errorMessage && (
+          <ConnectErrorText>{errorMessage}</ConnectErrorText>
+        )}
+
         {!compact && (
           <>
             <MetaRow>
diff --git a/clients/web/src/components/screens/ServerListScreen/ServerListScreen.test.tsx b/clients/web/src/components/screens/ServerListScreen/ServerListScreen.test.tsx
index 2c72927a65..79ef64dfda 100644
--- a/clients/web/src/components/screens/ServerListScreen/ServerListScreen.test.tsx
+++ b/clients/web/src/components/screens/ServerListScreen/ServerListScreen.test.tsx
@@ -162,6 +162,22 @@ describe("ServerListScreen", () => {
         container.querySelectorAll('[data-variant="errored"]'),
       ).toHaveLength(0);
     });
+
+    it("shows the failure reason only on the failed server's card (#2783)", () => {
+      renderWithMantine(
+        <ServerListScreen
+          {...baseProps}
+          erroredServerId="beta"
+          connectErrorMessage="Remote connect failed (500)"
+        />,
+      );
+      const alerts = screen.getAllByRole("alert");
+      expect(alerts).toHaveLength(1);
+      expect(alerts[0]).toHaveTextContent("Remote connect failed (500)");
+      expect(alerts[0]!.closest('[data-variant="errored"]')).toHaveTextContent(
+        "Beta",
+      );
+    });
   });
 
   describe("just-connected highlight (#1682)", () => {
diff --git a/clients/web/src/components/screens/ServerListScreen/ServerListScreen.tsx b/clients/web/src/components/screens/ServerListScreen/ServerListScreen.tsx
index d66109a14d..5694cd2ea5 100644
--- a/clients/web/src/components/screens/ServerListScreen/ServerListScreen.tsx
+++ b/clients/web/src/components/screens/ServerListScreen/ServerListScreen.tsx
@@ -48,6 +48,11 @@ export interface ServerListScreenProps {
    * draws a red border until another server is connected or attempted.
    */
   erroredServerId?: string;
+  /**
+   * Why that server's connection attempt failed (#2783), shown on the
+   * `erroredServerId` card so the reason outlasts the failure toast.
+   */
+  connectErrorMessage?: string;
   /**
    * Id of the server that just connected successfully (#1682). Its card draws
    * the green highlight border and scrolls into view — the success mirror of
@@ -190,6 +195,7 @@ export function ServerListScreen({
   writable = true,
   activeServer,
   erroredServerId,
+  connectErrorMessage,
   connectedServerId,
   onAddManually,
   onImportConfig,
@@ -252,6 +258,8 @@ export function ServerListScreen({
     onRemove,
     highlighted: highlightedServerIds?.includes(server.id) ?? false,
     errored: server.id === erroredServerId,
+    errorMessage:
+      server.id === erroredServerId ? connectErrorMessage : undefined,
     justConnected: server.id === connectedServerId,
     scrollOnHighlight: server.id === firstHighlightedId,
     onClearHighlight: onClearHighlight
diff --git a/clients/web/src/components/views/InspectorView/InspectorView.tsx b/clients/web/src/components/views/InspectorView/InspectorView.tsx
index 048837a617..9688ed97db 100644
--- a/clients/web/src/components/views/InspectorView/InspectorView.tsx
+++ b/clients/web/src/components/views/InspectorView/InspectorView.tsx
@@ -1174,6 +1174,7 @@ export function InspectorView({
                 writable={serverListWritable}
                 activeServer={dimCardsAgainst}
                 erroredServerId={erroredServerId}
+                connectErrorMessage={connectErrorMessage}
                 connectedServerId={connectedServerId}
                 onAddManually={onServerAdd}
                 onImportConfig={onServerImportConfig}
diff --git a/clients/web/src/components/views/InspectorView/types.ts b/clients/web/src/components/views/InspectorView/types.ts
index 538e6734c5..7aef67b68e 100644
--- a/clients/web/src/components/views/InspectorView/types.ts
+++ b/clients/web/src/components/views/InspectorView/types.ts
@@ -144,7 +144,8 @@ export interface ConnectionProps {
    * Last connection-level error message (handshake failure, OAuth start
    * failure, deep-link automation failure). Surfaced as `data-error-message`
    * on the header's `connection-status` testid so an automated driver can read
-   * *why* a connect failed without scraping a transient toast.
+   * *why* a connect failed without scraping a transient toast, and — for the
+   * same reason, but for people — on the `erroredServerId` card (#2783).
    */
   connectErrorMessage?: string;
   initializeResult?: InitializeResult;
diff --git a/clients/web/src/theme/Text.ts b/clients/web/src/theme/Text.ts
index 6d0052262b..c89cf0a19b 100644
--- a/clients/web/src/theme/Text.ts
+++ b/clients/web/src/theme/Text.ts
@@ -37,6 +37,20 @@ export const ThemeText = Text.extend({
         },
       };
     }
+    // The reason a server card's last connect attempt failed (#2783), kept on
+    // the card after the toast that first reported it auto-closes. The text
+    // is often a raw transport error carrying a URL or a JSON body, so it has
+    // to wrap inside the card rather than run under its border.
+    if (props.variant === "connectError") {
+      return {
+        root: {
+          color: "var(--inspector-danger-text)",
+          fontSize: "var(--mantine-font-size-sm)",
+          whiteSpace: "pre-wrap",
+          wordBreak: "break-word",
+        },
+      };
+    }
     // Two small, unobtrusive labels that sit in the footer row (#1682): the
     // build version (left) and the copyright notice (right), positioned by the
     // footer's `space-between` Group. Both are grey, single-line, and out of the