diff --git a/apps/client/src/features/base/components/grid/grid-container.tsx b/apps/client/src/features/base/components/grid/grid-container.tsx
index 803cf161..3334a2e8 100644
--- a/apps/client/src/features/base/components/grid/grid-container.tsx
+++ b/apps/client/src/features/base/components/grid/grid-container.tsx
@@ -210,6 +210,7 @@ export function GridContainer({
               table={table}
               baseId={baseId}
               columnOrder={table.getState().columnOrder}
+              loadedRowIds={rowIds}
               onPropertyCreated={handlePropertyCreated}
             />
           </SortableContext>
diff --git a/apps/client/src/features/base/components/grid/grid-header-cell.tsx b/apps/client/src/features/base/components/grid/grid-header-cell.tsx
index 9d54c80b..9fe7bebe 100644
--- a/apps/client/src/features/base/components/grid/grid-header-cell.tsx
+++ b/apps/client/src/features/base/components/grid/grid-header-cell.tsx
@@ -23,6 +23,8 @@ import {
   IconUserEdit,
 } from "@tabler/icons-react";
 import { PropertyMenuContent } from "@/features/base/components/property/property-menu";
+import { RowNumberHeaderCell } from "./row-number-header-cell";
+import { useRowSelection } from "@/features/base/hooks/use-row-selection";
 import classes from "@/features/base/styles/grid.module.css";
 
 const typeIcons: Record<string, typeof IconLetterT> = {
@@ -44,10 +46,12 @@ const typeIcons: Record<string, typeof IconLetterT> = {
 
 type GridHeaderCellProps = {
   header: Header<IBaseRow, unknown>;
+  loadedRowIds: string[];
 };
 
 export const GridHeaderCell = memo(function GridHeaderCell({
   header,
+  loadedRowIds,
 }: GridHeaderCellProps) {
   const property = header.column.columnDef.meta?.property as
     | IBaseProperty
@@ -55,6 +59,8 @@ export const GridHeaderCell = memo(function GridHeaderCell({
   const isRowNumber = header.column.id === "__row_number";
   const isPinned = header.column.getIsPinned();
   const pinOffset = isPinned ? header.column.getStart("left") : undefined;
+  const { selectionCount } = useRowSelection();
+  const hasSelection = selectionCount > 0;
 
   const [activePropertyMenu, setActivePropertyMenu] = useAtom(activePropertyMenuAtom) as unknown as [string | null, (val: string | null) => void];
   const menuOpened = activePropertyMenu === header.column.id;
@@ -118,7 +124,7 @@ export const GridHeaderCell = memo(function GridHeaderCell({
   return (
     <div
       ref={combinedRef}
-      className={`${classes.headerCell} ${isPinned ? classes.headerCellPinned : ""}`}
+      className={`${classes.headerCell} ${isPinned ? classes.headerCellPinned : ""} ${hasSelection ? classes.hasSelection : ""}`}
       style={{
         ...(isPinned ? { left: pinOffset } : {}),
         ...(isRowNumber ? {} : { cursor: "pointer" }),
@@ -129,7 +135,7 @@ export const GridHeaderCell = memo(function GridHeaderCell({
       {...(isSortableDisabled ? {} : listeners)}
     >
       {isRowNumber ? (
-        flexRender(header.column.columnDef.header, header.getContext())
+        <RowNumberHeaderCell loadedRowIds={loadedRowIds} />
       ) : (
         <div className={classes.headerCellContent}>
           {TypeIcon && (
diff --git a/apps/client/src/features/base/components/grid/grid-header.tsx b/apps/client/src/features/base/components/grid/grid-header.tsx
index add400fe..9c026bdd 100644
--- a/apps/client/src/features/base/components/grid/grid-header.tsx
+++ b/apps/client/src/features/base/components/grid/grid-header.tsx
@@ -11,6 +11,7 @@ type GridHeaderProps = {
   // Passed explicitly to break memo when columns change
   // (table ref is stable from useReactTable, so memo won't fire without this)
   columnOrder: ColumnOrderState;
+  loadedRowIds: string[];
   onPropertyCreated?: () => void;
 };
 
@@ -19,6 +20,7 @@ export const GridHeader = memo(function GridHeader({
   baseId,
   // eslint-disable-next-line @typescript-eslint/no-unused-vars
   columnOrder: _columnOrder,
+  loadedRowIds,
   onPropertyCreated,
 }: GridHeaderProps) {
   const headerGroups = table.getHeaderGroups();
@@ -26,7 +28,7 @@ export const GridHeader = memo(function GridHeader({
   return (
     <div className={classes.headerRow} role="row">
       {headerGroups[0]?.headers.map((header) => (
-        <GridHeaderCell key={header.id} header={header} />
+        <GridHeaderCell key={header.id} header={header} loadedRowIds={loadedRowIds} />
       ))}
       {baseId && (
         <CreatePropertyPopover
diff --git a/apps/client/src/features/base/components/grid/row-number-header-cell.tsx b/apps/client/src/features/base/components/grid/row-number-header-cell.tsx
new file mode 100644
index 00000000..0a0c1a01
--- /dev/null
+++ b/apps/client/src/features/base/components/grid/row-number-header-cell.tsx
@@ -0,0 +1,48 @@
+import { memo, useMemo } from "react";
+import { Checkbox, Tooltip } from "@mantine/core";
+import { useRowSelection } from "@/features/base/hooks/use-row-selection";
+import classes from "@/features/base/styles/grid.module.css";
+
+type RowNumberHeaderCellProps = {
+  loadedRowIds: string[];
+};
+
+export const RowNumberHeaderCell = memo(function RowNumberHeaderCell({
+  loadedRowIds,
+}: RowNumberHeaderCellProps) {
+  const { selectedIds, toggleAll } = useRowSelection();
+
+  const { checked, indeterminate } = useMemo(() => {
+    if (loadedRowIds.length === 0) {
+      return { checked: false, indeterminate: false };
+    }
+    const selectedInLoaded = loadedRowIds.reduce(
+      (acc, id) => (selectedIds.has(id) ? acc + 1 : acc),
+      0,
+    );
+    return {
+      checked: selectedInLoaded === loadedRowIds.length,
+      indeterminate:
+        selectedInLoaded > 0 && selectedInLoaded < loadedRowIds.length,
+    };
+  }, [loadedRowIds, selectedIds]);
+
+  if (loadedRowIds.length === 0) return null;
+
+  return (
+    <div className={classes.rowNumberHeaderInner}>
+      <span className={classes.rowNumberHeaderHash}>#</span>
+      <span className={classes.rowNumberHeaderCheckbox}>
+        <Tooltip label="Select all loaded rows" withinPortal>
+          <Checkbox
+            size="xs"
+            checked={checked}
+            indeterminate={indeterminate}
+            onChange={() => toggleAll(loadedRowIds)}
+            aria-label="Select all loaded rows"
+          />
+        </Tooltip>
+      </span>
+    </div>
+  );
+});
diff --git a/apps/client/src/features/base/styles/grid.module.css b/apps/client/src/features/base/styles/grid.module.css
index e66a8199..73466d68 100644
--- a/apps/client/src/features/base/styles/grid.module.css
+++ b/apps/client/src/features/base/styles/grid.module.css
@@ -347,3 +347,30 @@
 .rowSelected .cell {
   background: light-dark(var(--mantine-color-blue-0), var(--mantine-color-dark-6));
 }
+
+.rowNumberHeaderInner {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 100%;
+  height: 100%;
+}
+
+.rowNumberHeaderHash {
+  color: light-dark(var(--mantine-color-gray-5), var(--mantine-color-dark-3));
+  font-size: var(--mantine-font-size-xs);
+}
+
+.rowNumberHeaderCheckbox {
+  display: none;
+}
+
+.headerCell:hover .rowNumberHeaderHash,
+.hasSelection .rowNumberHeaderHash {
+  display: none;
+}
+
+.headerCell:hover .rowNumberHeaderCheckbox,
+.hasSelection .rowNumberHeaderCheckbox {
+  display: inline-flex;
+}