diff --git a/frontend/index.html b/frontend/index.html
index e11aef1..b7a4bec 100644
--- a/frontend/index.html
+++ b/frontend/index.html
@@ -1117,6 +1117,9 @@
 							<span data-l10n="Sort:">Sort:</span>
 							<span class="pysim-fs-sort-pill px-2 py-0.5 rounded cursor-pointer bg-blue-600 text-white" data-fs-sort="fid" onclick="pysimFsSetSort('fid')">FID</span>
 							<span class="pysim-fs-sort-pill px-2 py-0.5 rounded cursor-pointer bg-gray-200 dark:bg-slate-700 text-gray-700 dark:text-slate-300" data-fs-sort="name" onclick="pysimFsSetSort('name')" data-l10n="Name">Name</span>
+							<span class="mx-1 text-gray-400 dark:text-slate-600">·</span>
+							<button type="button" onclick="pysimFsExpandAll()" class="text-xs text-blue-600 dark:text-blue-400 hover:underline" data-l10n="Expand all">Expand all</button>
+							<button type="button" onclick="pysimFsCollapseAll()" class="text-xs text-blue-600 dark:text-blue-400 hover:underline" data-l10n="Collapse all">Collapse all</button>
 						</div>
 						<div class="flex items-center gap-1 mb-1 text-gray-500 dark:text-slate-400">
 							<span data-l10n="Filter:">Filter:</span>
@@ -16339,6 +16342,7 @@ function pysimFsFilterSetEntry(entry, on) {
 	localStorage.setItem('simple_fs_filter', JSON.stringify(Array.from(pysimFsFilter)));
 	pysimFsFilterRender();
 	pysimFsRenderTree();
+	pysimFsAutoExpandForFilter();
 }
 
 // The cross-reference inverted to service number -> feature name, per file
@@ -16382,6 +16386,7 @@ function pysimFsSetFilterToService(table, n) {
 	localStorage.setItem('simple_fs_filter', JSON.stringify(Array.from(pysimFsFilter)));
 	pysimFsFilterRender();
 	pysimFsRenderTree();
+	pysimFsAutoExpandForFilter();
 }
 
 // Whether a file node passes the active filter.  An empty selection and
@@ -16684,6 +16689,42 @@ async function pysimFsToggleDir(path) {
 	if (node.expanded) pysimRefresh();
 }
 
+// Expand every directory that exists (skipping ones the probe already found
+// absent), loading children on demand.  Also the auto-action after a filter
+// narrows to a specific category, so the matched files are visible.
+async function pysimFsExpandAll() {
+	const stack = [pysimFsTreeRoot];
+	while (stack.length) {
+		const node = stack.pop();
+		if (!node || !node.isDir) continue;
+		if (node.exists === false) continue;
+		if (!node.children) {
+			await pysimFsLoadChildren(node);
+			if (node.exists === false) continue;
+		}
+		node.expanded = true;
+		for (const c of (node.children || [])) if (c.isDir) stack.push(c);
+	}
+	pysimFsRenderTree();
+}
+
+function pysimFsCollapseAll() {
+	const stack = [pysimFsTreeRoot];
+	while (stack.length) {
+		const node = stack.pop();
+		if (!node || !node.isDir) continue;
+		node.expanded = false;
+		for (const c of (node.children || [])) if (c.isDir) stack.push(c);
+	}
+	pysimFsRenderTree();
+}
+
+// A filter that narrows to a specific category expands the tree so the
+// matched files are shown; "All"/empty leaves the tree as-is.
+function pysimFsAutoExpandForFilter() {
+	if (pysimFsFilter.size > 0 && !pysimFsFilter.has(FS_FILTER_ALL)) pysimFsExpandAll();
+}
+
 let pysimFsSelected = null;
 
 function pysimFsInfoHtml(sel, name, opts) {
@@ -28074,6 +28115,8 @@ const LANG_RU = {
 	'CB-related': 'Связанное с CB',
 	'Custom files': 'Пользовательские файлы',
 	'Selected: {n}': 'Выбрано: {n}',
+	'Expand all': 'Развернуть все',
+	'Collapse all': 'Свернуть все',
 	'Probe all files': 'Проверить все файлы',
 	'Feature': 'Функция',
 	'SST': 'SST',
diff --git a/frontend/tests/fs_filter.test.js b/frontend/tests/fs_filter.test.js
index 2a447f5..b6bc490 100644
--- a/frontend/tests/fs_filter.test.js
+++ b/frontend/tests/fs_filter.test.js
@@ -6,7 +6,7 @@ const path = require('node:path');
 const html = fs.readFileSync(path.join(__dirname, '..', 'index.html'), 'utf8');
 
 function extractFunc(src, name) {
-	const re = new RegExp('function\\s+' + name + '\\s*\\([^)]*\\)\\s*\\{');
+	const re = new RegExp('(?:async\\s+)?function\\s+' + name + '\\s*\\([^)]*\\)\\s*\\{');
 	const m = re.exec(src);
 	if (!m) throw new Error('function ' + name + ' not found');
 	let i = m.index + m[0].length - 1;
@@ -59,6 +59,8 @@ let _fsFilterPathsKey = null;
 let pysimCustomFiles = [];
 const _store = {};
 let _treeRenders = 0;
+let pysimFsTreeRoot = null;   // expand-all walks this; null = nothing to expand
+let pysimFsLoadChildren = async node => { if (!node.children) node.children = []; };
 
 globalThis.localStorage = {
 	getItem: k => (Object.prototype.hasOwnProperty.call(_store, k) ? _store[k] : null),
@@ -121,7 +123,8 @@ for (const f of ['fsFilterServiceOptions', 'fsFilterIndexBuild', 'fsFilterIndex'
 	'fsFilterPathsKeyOf', 'pysimFsFilterPathsInvalidate', 'pysimFsFilterMatchingPaths',
 	'pysimFsFilterMatch', 'pysimFsFilterShow', 'pysimFsFilterLabel',
 	'pysimFsFilterSummary', 'pysimFsFilterRender', 'pysimFsFilterToggle',
-	'pysimFsFilterSetEntry', 'pysimFsFilterRestore', 'pysimFsNodePath']) {
+	'pysimFsFilterSetEntry', 'pysimFsFilterRestore', 'pysimFsNodePath',
+	'pysimFsExpandAll', 'pysimFsCollapseAll', 'pysimFsAutoExpandForFilter']) {
 	code += extractFunc(html, f) + '\n';
 }
 for (const c of ['FS_FILTER_GROUPS', 'FS_FILTER_GROUP_ORDER', 'SERVICES_FS_MAP']) code += extractConst(html, c);
@@ -454,6 +457,46 @@ test('the button turns blue when a filter is active and back for all', () => {
 	assert.strictEqual(dom.btn.classes.has('text-gray-700'), true);
 });
 
+test('expand all and collapse all walk the directory tree, skipping absent DFs', async () => {
+	const telecom = { name: 'DF.TELECOM', fid: '7F10', isDir: true, exists: true, expanded: false,
+		parent: null, children: [
+			{ name: 'DF.PHONEBOOK', fid: '5F3A', isDir: true, exists: true, expanded: false, parent: null, children: null },
+		] };
+	const gsm = { name: 'DF.GSM', fid: '7F20', isDir: true, exists: false, expanded: false, parent: null, children: null };
+	pysimFsTreeRoot = { name: 'MF', fid: '3F00', isDir: true, exists: true, expanded: true, parent: null,
+		children: [gsm, telecom] };
+	let loads = 0;
+	pysimFsLoadChildren = async node => { if (!node.children) { node.children = []; } loads++; };
+	try {
+		_treeRenders = 0;
+		await pysimFsExpandAll();
+		assert.strictEqual(pysimFsTreeRoot.expanded, true);
+		assert.strictEqual(gsm.expanded, false, 'an absent DF is not expanded');
+		assert.strictEqual(telecom.expanded, true);
+		assert.strictEqual(telecom.children[0].expanded, true);
+		assert.ok(loads > 0, 'lazy children are loaded on demand');
+		assert.strictEqual(_treeRenders, 1);
+
+		pysimFsCollapseAll();
+		assert.strictEqual(pysimFsTreeRoot.expanded, false);
+		assert.strictEqual(telecom.expanded, false);
+		assert.strictEqual(telecom.children[0].expanded, false);
+	} finally {
+		pysimFsTreeRoot = null;
+	}
+});
+
+test('auto-expand fires only for a non-"all" filter', () => {
+	// expand-all (with a null tree) still re-renders once; pin the branch
+	pysimFsFilter = new Set(['all']);
+	_treeRenders = 0;
+	pysimFsAutoExpandForFilter();
+	assert.strictEqual(_treeRenders, 0, '"all" does not expand');
+	pysimFsFilter = new Set(['identifiers']);
+	pysimFsAutoExpandForFilter();
+	assert.strictEqual(_treeRenders, 1, 'a category expands the tree');
+});
+
 test('the menu marks the saved selection', () => {
 	pysimFsFilter = new Set(['svc:Short Message Storage (SMS)', 'identifiers']);
 	dom.menu = fakeMenu();
@@ -510,7 +553,7 @@ test('the checkbox rows keep "all" exclusive and persist the selection', () => {
 	pysimFsFilterSetEntry('sms', true);
 	assert.deepStrictEqual([...pysimFsFilter], ['sms']);
 	assert.strictEqual(_store.simple_fs_filter, '["sms"]');
-	assert.strictEqual(_treeRenders, 2);
+	assert.strictEqual(_treeRenders, 3);   // render + the auto-expand's render
 	assert.strictEqual(box('sms').checked, true);
 	assert.strictEqual(box('all').checked, false);
 	assert.strictEqual(dom.btn.textContent, 'SMS-related');
diff --git a/frontend/tests/fs_service_link.test.js b/frontend/tests/fs_service_link.test.js
index b1e51ba..47393ad 100644
--- a/frontend/tests/fs_service_link.test.js
+++ b/frontend/tests/fs_service_link.test.js
@@ -51,6 +51,7 @@ let _fsFilterPathsKey = null;
 const _store = {};
 let _renders = 0;
 let _treeRenders = 0;
+let pysimFsTreeRoot = null;   // expand-all walks this; null = nothing to expand
 
 globalThis.localStorage = {
 	getItem: k => (Object.prototype.hasOwnProperty.call(_store, k) ? _store[k] : null),
@@ -64,10 +65,12 @@ globalThis.pysimFsRenderTree = () => { _treeRenders++; };
 
 let code = '';
 for (const f of ['servicesFeatureByNumber', 'pysimFsFilterBtnHtml', 'pysimFsSetFilterToService',
-	'pysimFsFilterPathsInvalidate']) {
+	'pysimFsFilterPathsInvalidate', 'pysimFsExpandAll', 'pysimFsCollapseAll',
+	'pysimFsAutoExpandForFilter']) {
 	code += extractFunc(html, f) + '\n';
 }
 for (const c of ['SERVICES_CROSS_REF', 'SERVICES_FS_MAP']) code += extractConst(html, c);
+code += "var FS_FILTER_ALL = 'all';\n";
 eval(code);
 
 test('servicesFeatureByNumber inverts the cross-reference per file table', () => {
@@ -107,12 +110,12 @@ test('pysimFsSetFilterToService narrows the tree to that service', () => {
 	assert.deepStrictEqual([...pysimFsFilter], ['svc:Fixed Dialling Numbers (FDN)']);
 	assert.strictEqual(_store.simple_fs_filter, JSON.stringify(['svc:Fixed Dialling Numbers (FDN)']));
 	assert.strictEqual(_renders, 1);
-	assert.strictEqual(_treeRenders, 1);
+	assert.strictEqual(_treeRenders, 2);   // render + the auto-expand's render
 	// a capability-only service changes nothing
 	pysimFsSetFilterToService('ust', 99);
 	assert.deepStrictEqual([...pysimFsFilter], ['svc:Fixed Dialling Numbers (FDN)']);
 	assert.strictEqual(_renders, 1);
-	assert.strictEqual(_treeRenders, 1);
+	assert.strictEqual(_treeRenders, 2);
 });
 
 test('the four service-table fields carry their table, EF.ACC carries none', () => {