diff --git a/media/webview.css b/media/webview.css
index e01bd73..dda2dce 100644
--- a/media/webview.css
+++ b/media/webview.css
@@ -1157,7 +1157,7 @@ body.vscode-high-contrast #grid-container.cm-on {
 .col-chooser-item {
     display: flex;
     align-items: center;
-    gap: 7px;
+    gap: 6px;
     padding: 4px 6px;
     font-size: 12px;
     cursor: pointer;
@@ -1165,6 +1165,31 @@ body.vscode-high-contrast #grid-container.cm-on {
 }
 .col-chooser-item:hover { background: var(--vscode-list-hoverBackground, #2a2d2e); }
 .col-chooser-item input { cursor: pointer; margin: 0; flex: none; accent-color: var(--vscode-focusBorder, #007fd4); }
+.col-chooser-master {
+    display: flex;
+    align-items: center;
+    gap: 6px;
+    padding: 6px;
+    margin: 6px 0;
+    font-size: 12px;
+    font-weight: 600;
+    cursor: pointer;
+    border-radius: 3px;
+    position: relative;
+}
+.col-chooser-master::after {
+    content: '';
+    position: absolute;
+    left: 0;
+    right: 0;
+    bottom: -4px;
+    height: 1px;
+    background: var(--vscode-menu-border, #454545);
+}
+.col-chooser-master:hover { background: var(--vscode-list-hoverBackground, #2a2d2e); }
+.col-chooser-master input { cursor: pointer; margin: 0; flex: none; accent-color: var(--vscode-focusBorder, #007fd4); }
+.col-chooser-master-label { flex: 1; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
+.col-chooser-master-count { font-size: 11px; font-weight: 400; opacity: 0.6; flex: none; }
 .col-chooser-label { overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
 .goto-error {
     margin-top: 6px;
diff --git a/src/webview.ts b/src/webview.ts
index c1fcb10..16228c6 100644
--- a/src/webview.ts
+++ b/src/webview.ts
@@ -174,10 +174,11 @@ export function getWebviewContent(
             <span class="goto-label" style="margin:0;">Columns</span>
         </div>
         <input id="col-chooser-search" class="csv-filter-input" type="text" placeholder="Search columns…" spellcheck="false">
-        <div class="csv-filter-actions">
-            <button id="col-chooser-showall" type="button" class="csv-filter-link">Show all</button>
-            <button id="col-chooser-hideall" type="button" class="csv-filter-link">Hide all</button>
-        </div>
+        <label id="col-chooser-master" class="col-chooser-master">
+            <input id="col-chooser-master-cb" type="checkbox">
+            <span id="col-chooser-master-label" class="col-chooser-master-label">Select all</span>
+            <span id="col-chooser-master-count" class="col-chooser-master-count"></span>
+        </label>
         <div id="col-chooser-list" class="col-chooser-list"></div>
     </div>
 
diff --git a/src/webview/features/column-chooser.ts b/src/webview/features/column-chooser.ts
index e4fd98d..1fb11a1 100644
--- a/src/webview/features/column-chooser.ts
+++ b/src/webview/features/column-chooser.ts
@@ -3,13 +3,13 @@ import { closeAllPopups } from './popups';
 
 // ── Column chooser (show / hide columns) ────────────────────────────────────
 // A toolbar dropdown listing every data column with a checkbox to toggle its
-// visibility. A search box filters the list by column name, and Show all / Hide
-// all flip every column at once (Hide all, then search and re-check the few you
-// want). Visibility is applied via AG Grid (setColumnsVisible) and mirrored into
-// state.hiddenCols (0-based data-column indices) so it survives a grid rebuild —
-// e.g. a paged-view page change re-runs buildGrid, which re-applies `hide` from
-// this set. In-memory only (not persisted across reload), matching the freeze
-// features. Column insert/delete clears the set (see delete-row-col).
+// visibility. A search box filters the list by column name. A pinned tri-state
+// "Select all" master checkbox above the list reflects and controls the columns.
+// Visibility is applied via AG Grid (setColumnsVisible) and mirrored into state.hiddenCols
+// (0-based data-column indices) so it survives a grid rebuild - e.g. a paged-view
+// page change re-runs buildGrid, which re-applies `hide` from this set. In-memory
+// only (not persisted across reload), matching the freeze features. Column
+// insert/delete clears the set (see delete-row-col).
 
 let searchQuery = '';
 
@@ -18,34 +18,63 @@ function setColHidden(colIndex: number, hidden: boolean): void {
     else state.hiddenCols.delete(colIndex);
     state.gridApi?.setColumnsVisible(['col_' + colIndex], !hidden);
     updateButton();
+    syncMaster();
 }
 
-function allColIds(): string[] {
-    const n = (state.data[0] ?? []).length;
-    const ids: string[] = [];
-    for (let c = 0; c < n; c++) ids.push('col_' + c);
-    return ids;
+function colLabel(header: string[], c: number): string {
+    const name = header[c] ?? '';
+    return name !== '' ? name : '(column ' + (c + 1) + ')';
+}
+
+function visibleColIndices(): number[] {
+    const header = state.data[0] ?? [];
+    const q = searchQuery.trim().toLowerCase();
+    const out: number[] = [];
+    for (let c = 0; c < header.length; c++) {
+        if (q && !colLabel(header, c).toLowerCase().includes(q)) continue;
+        out.push(c);
+    }
+    return out;
 }
 
-function showAll(): void {
-    state.hiddenCols.clear();
-    state.gridApi?.setColumnsVisible(allColIds(), true);
+function setVisibleColsHidden(hidden: boolean): void {
+    const cols = visibleColIndices();
+    if (cols.length === 0) return;
+    if (!hidden && searchQuery.trim() === '') {
+        state.hiddenCols.clear();
+        state.gridApi?.setColumnsVisible(allColIds(), true);
+    } else {
+        for (const c of cols) {
+            if (hidden) state.hiddenCols.add(c);
+            else state.hiddenCols.delete(c);
+        }
+        state.gridApi?.setColumnsVisible(cols.map(c => 'col_' + c), !hidden);
+    }
     buildList();
     updateButton();
 }
 
-function hideAll(): void {
+function allColIds(): string[] {
     const n = (state.data[0] ?? []).length;
-    state.hiddenCols.clear();
-    for (let c = 0; c < n; c++) state.hiddenCols.add(c);
-    state.gridApi?.setColumnsVisible(allColIds(), false);
-    buildList();
-    updateButton();
+    const ids: string[] = [];
+    for (let c = 0; c < n; c++) ids.push('col_' + c);
+    return ids;
 }
 
-function colLabel(header: string[], c: number): string {
-    const name = header[c] ?? '';
-    return name !== '' ? name : '(column ' + (c + 1) + ')';
+function syncMaster(): void {
+    const cb = document.getElementById('col-chooser-master-cb') as HTMLInputElement | null;
+    const count = document.getElementById('col-chooser-master-count');
+    const label = document.getElementById('col-chooser-master-label');
+    if (!cb) return;
+    const cols = visibleColIndices();
+    const visible = cols.reduce((n, c) => n + (state.hiddenCols.has(c) ? 0 : 1), 0);
+    const total = cols.length;
+
+    cb.checked = total > 0 && visible === total;
+    cb.indeterminate = visible > 0 && visible < total;
+    cb.disabled = total === 0;
+    if (count) count.textContent = total > 0 ? `${visible} / ${total}` : '';
+    if (label) label.textContent = searchQuery.trim() ? 'Select all matches' : 'Select all';
 }
 
 function buildList(): void {
@@ -53,13 +82,9 @@ function buildList(): void {
     if (!list) return;
     list.innerHTML = '';
     const header = state.data[0] ?? [];
-    const q = searchQuery.trim().toLowerCase();
-    let shown = 0;
-    for (let c = 0; c < header.length; c++) {
-        const label = colLabel(header, c);
-        if (q && !label.toLowerCase().includes(q)) continue;
-        shown++;
+    const cols = visibleColIndices();
 
+    for (const c of cols) {
         const row = document.createElement('label');
         row.className = 'col-chooser-item';
 
@@ -71,19 +96,21 @@ function buildList(): void {
 
         const span = document.createElement('span');
         span.className = 'col-chooser-label';
-        span.textContent = label;
+        span.textContent = colLabel(header, c);
 
         row.appendChild(cb);
         row.appendChild(span);
         list.appendChild(row);
     }
 
-    if (shown === 0) {
+    if (cols.length === 0) {
         const empty = document.createElement('div');
         empty.className = 'csv-filter-empty';
         empty.textContent = 'No matching columns';
         list.appendChild(empty);
     }
+
+    syncMaster();
 }
 
 function updateButton(): void {
@@ -99,10 +126,10 @@ function openChooser(): void {
     if (search) search.value = '';
     buildList();
     pop.classList.remove('hidden');
-    const r  = btn.getBoundingClientRect();
+    const r = btn.getBoundingClientRect();
     const pw = pop.offsetWidth || 220;
     const vw = window.innerWidth;
-    pop.style.top  = (r.bottom + 4) + 'px';
+    pop.style.top = (r.bottom + 4) + 'px';
     pop.style.left = Math.max(4, Math.min(r.left, vw - pw - 4)) + 'px';
     search?.focus();
 }
@@ -121,8 +148,8 @@ export function setupColumnChooser(): void {
         if (!wasOpen) openChooser();
     });
 
-    document.getElementById('col-chooser-showall')?.addEventListener('click', showAll);
-    document.getElementById('col-chooser-hideall')?.addEventListener('click', hideAll);
+    const master = document.getElementById('col-chooser-master-cb') as HTMLInputElement | null;
+    master?.addEventListener('change', () => setVisibleColsHidden(!master.checked));
 
     const search = document.getElementById('col-chooser-search') as HTMLInputElement | null;
     search?.addEventListener('input', () => {