diff --git a/src/features/database/Database.module.css b/src/features/database/Database.module.css
index fa103b667..909df5869 100644
--- a/src/features/database/Database.module.css
+++ b/src/features/database/Database.module.css
@@ -1259,3 +1259,18 @@
   flex: none;
   width: 2px;
 }
+
+/* Wrap large values instead of laying megabytes out as one line. */
+.largeCellEditor {
+  display: block;
+  box-sizing: border-box;
+  width: 100%;
+  height: min(60vh, 480px);
+  padding: 8px;
+  font: inherit;
+  color: inherit;
+  background: inherit;
+  white-space: pre-wrap;
+  overflow-wrap: anywhere;
+  resize: vertical;
+}
diff --git a/src/features/database/Grid.test.tsx b/src/features/database/Grid.test.tsx
index 75b5e24fa..2c7e73aa5 100644
--- a/src/features/database/Grid.test.tsx
+++ b/src/features/database/Grid.test.tsx
@@ -2,7 +2,8 @@ import { installKeyboardDispatcher, useKeymap } from "@/platform/keymap";
 import { registerActions } from "@/platform/actions";
 import { fireEvent, render, screen } from "@testing-library/react";
 import { afterEach, describe, expect, it, vi } from "vitest";
-import { Grid } from "./Grid";
+import { CELL_PREVIEW_LIMIT, cellPreview, Grid } from "./Grid";
+import { exportData } from "./export";
 
 vi.mock("@tanstack/react-virtual", () => ({
   useVirtualizer: ({ count }: { count: number }) => ({
@@ -72,3 +73,59 @@ describe("database grid", () => {
     ]);
   });
 });
+
+describe("large database cells", () => {
+  const full = JSON.stringify({ text: "\u8bf4\u660e text \u6df7\u5408 ".repeat(200_000), tail: "complete" });
+  const columns = [{ name: "payload", type: "jsonb" }];
+
+  it("preserves short values and truncates only beyond the preview limit", () => {
+    for (const value of ["", "hello", "\u4e2d".repeat(CELL_PREVIEW_LIMIT)]) expect(cellPreview(value)).toBe(value);
+    expect(cellPreview(full)).toBe(full.slice(0, CELL_PREVIEW_LIMIT) + "\u2026");
+    expect(cellPreview("a".repeat(999) + "\ud83d\ude00tail")).toBe("a".repeat(999) + "\u2026");
+  });
+
+  it("bounds rendered text while copying and exporting the complete value", () => {
+    const writeText = vi.fn();
+    Object.defineProperty(navigator, "clipboard", { configurable: true, value: { writeText } });
+    render(<Grid columns={columns} rowCount={1} value={() => full} />);
+    const cell = screen.getByRole("gridcell");
+    expect(cell.textContent).toBe(cellPreview(full));
+    expect(cell.title).toBe(full.slice(0, 2000));
+    fireEvent.mouseDown(cell, { button: 0 });
+    fireEvent.keyDown(screen.getByRole("grid"), { key: "c", ctrlKey: true });
+    expect(writeText).toHaveBeenCalledWith(full);
+    expect(JSON.parse(exportData("json", { columns, rows: [[full]], table: "big", driver: "postgres" }))).toEqual([
+      { payload: full },
+    ]);
+  });
+
+  it("edits the full large value in a dialog and supports cancel and apply", () => {
+    const onEdit = vi.fn();
+    render(<Grid columns={columns} rowCount={1} value={() => full} editable onEdit={onEdit} />);
+    fireEvent.doubleClick(screen.getByRole("gridcell"));
+    expect(screen.getByRole("dialog")).toBeTruthy();
+    const editor = screen.getByRole("textbox") as HTMLTextAreaElement;
+    expect(editor.tagName).toBe("TEXTAREA");
+    expect(editor.value).toBe(full);
+    fireEvent.change(editor, { target: { value: full + "changed" } });
+    fireEvent.click(screen.getByRole("button", { name: "Cancel" }));
+    expect(onEdit).not.toHaveBeenCalled();
+    fireEvent.doubleClick(screen.getByRole("gridcell"));
+    fireEvent.change(screen.getByRole("textbox"), { target: { value: full + "changed" } });
+    fireEvent.click(screen.getByRole("button", { name: "Apply" }));
+    expect(onEdit).toHaveBeenCalledWith(0, 0, full + "changed");
+    expect(screen.queryByRole("dialog")).toBeNull();
+  });
+
+  it("keeps short values in the inline editor and preserves null display", () => {
+    const onEdit = vi.fn();
+    const { rerender } = render(<Grid columns={columns} rowCount={1} value={() => "short"} editable onEdit={onEdit} />);
+    fireEvent.doubleClick(screen.getByRole("gridcell"));
+    expect(screen.getByRole("textbox").tagName).toBe("INPUT");
+    fireEvent.change(screen.getByRole("textbox"), { target: { value: "updated" } });
+    fireEvent.keyDown(screen.getByRole("textbox"), { key: "Enter" });
+    expect(onEdit).toHaveBeenCalledWith(0, 0, "updated");
+    rerender(<Grid columns={columns} rowCount={1} value={() => null} />);
+    expect(screen.getByRole("gridcell").textContent).toBe("<null>");
+  });
+});
diff --git a/src/features/database/Grid.tsx b/src/features/database/Grid.tsx
index 3b05b4f67..0865878c1 100644
--- a/src/features/database/Grid.tsx
+++ b/src/features/database/Grid.tsx
@@ -6,7 +6,7 @@
 import { useEffect, useMemo, useRef, useState, type ClipboardEvent, type KeyboardEvent, type MouseEvent } from "react";
 import { useVirtualizer } from "@tanstack/react-virtual";
 import clsx from "clsx";
-import { Icon, showContextMenu, type MenuItem } from "@/ui";
+import { Dialog, Icon, showContextMenu, type MenuItem } from "@/ui";
 import { parseDelimited, toCsv, toTsv, type Cell } from "./model";
 import styles from "./Database.module.css";
 import { tx } from "@/platform/i18n";
@@ -69,6 +69,17 @@ interface Sel {
   c1: number;
 }
 
+export const CELL_PREVIEW_LIMIT = 1000;
+
+/** Bound text layout without changing the underlying value or splitting a surrogate pair. */
+export function cellPreview(value: string): string {
+  if (value.length <= CELL_PREVIEW_LIMIT) return value;
+  let end = CELL_PREVIEW_LIMIT;
+  const last = value.charCodeAt(end - 1);
+  if (last >= 0xd800 && last <= 0xdbff) end--;
+  return value.slice(0, end) + "\u2026";
+}
+
 const ROW_H = 24;
 const NUM_W = 48;
 
@@ -103,7 +114,7 @@ export function Grid(props: GridProps) {
     window.addEventListener("mouseup", stop);
     return () => window.removeEventListener("mouseup", stop);
   }, []);
-  const [editing, setEditing] = useState<{ row: number; col: number; text: string } | null>(null);
+  const [editing, setEditing] = useState<{ row: number; col: number; text: string; dialog: boolean } | null>(null);
   const columnKey = columns.map((c) => c.name).join("\u0000");
   const [widths, setWidths] = useState<number[]>([]);
   const [numeric, setNumeric] = useState<boolean[]>([]);
@@ -171,7 +182,8 @@ export function Grid(props: GridProps) {
 
   const startEdit = (row: number, col: number) => {
     if (!editable || props.rowState?.(row) === "deleted") return;
-    setEditing({ row, col, text: value(row, col) ?? "" });
+    const text = value(row, col) ?? "";
+    setEditing({ row, col, text, dialog: text.length > CELL_PREVIEW_LIMIT });
   };
 
   const onKeyDown = (e: KeyboardEvent<HTMLDivElement>) => {
@@ -302,6 +314,29 @@ export function Grid(props: GridProps) {
       onPaste={onPaste}
       onContextMenu={onContextMenu}
     >
+      {editing?.dialog && (
+        <Dialog
+          open
+          title={`Edit ${columns[editing.col]!.name}`}
+          width={720}
+          onClose={() => setEditing(null)}
+          buttons={[
+            { label: "Cancel", role: "cancel", onClick: () => setEditing(null) },
+            { label: "Apply", role: "default", onClick: commit },
+          ]}
+        >
+          <textarea
+            className={styles.largeCellEditor}
+            aria-label={`Edit ${columns[editing.col]!.name}`}
+            value={editing.text}
+            spellCheck={false}
+            wrap="soft"
+            onContextMenu={(e) => e.stopPropagation()}
+            onChange={(e) => setEditing({ ...editing, text: e.target.value })}
+            onKeyDown={(e) => e.stopPropagation()}
+          />
+        </Dialog>
+      )}
       <div className={styles.gridInner} style={{ width: totalWidth, height: virtualizer.getTotalSize() + ROW_H }}>
         <div className={clsx(styles.gridRow, styles.gridHeader)} style={{ gridTemplateColumns: template }} role="row">
           <div className={styles.rowNumber} />
@@ -368,7 +403,7 @@ export function Grid(props: GridProps) {
                 {state === "inserted" ? "+" : (props.rowNumber?.(r) ?? firstRowNumber + r)}
               </div>
               {columns.map((_, c) => {
-                if (editing && editing.row === r && editing.col === c) {
+                if (editing && !editing.dialog && editing.row === r && editing.col === c) {
                   return (
                     <input
                       key={c}
@@ -407,7 +442,11 @@ export function Grid(props: GridProps) {
                     onDoubleClick={() => startEdit(r, c)}
                     title={val != null && val.length > 40 ? val.slice(0, 2000) : undefined}
                   >
-                    {val === null ? <span className={styles.null}>&lt;null&gt;</span> : displayed(val, !!numeric[c])}
+                    {val === null ? (
+                      <span className={styles.null}>&lt;null&gt;</span>
+                    ) : (
+                      cellPreview(displayed(val, !!numeric[c]))
+                    )}
                   </div>
                 );
               })}