diff --git a/AGENTS.md b/AGENTS.md
index 07ac8f017..4006cfc7f 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -1271,7 +1271,8 @@ audit (#1207) locked in. New CTAs:
 | Render sub-views inside a Pattern A section (e.g. protests / submissions current-vs-archive) | `?view=<slug>` query param + a server-rendered `.chip-row` of real anchors (each carries `data-active="true|false"` + `aria-selected`). Reference: the protests / submissions chip rows in `web/pages/admin.bans.php` (`?section=protests&view=archive` / `?section=submissions&view=archive`). Pre-#1275 the chips called `Swap2ndPane()` — a `web/scripts/sourcebans.js` helper deleted at #1123 D1, leaving them dead — and the page rendered both views simultaneously. The new shape only renders the active view's data path; back/forward and link sharing both work. |
 | Lay out a sub-paged admin route's chrome (the 14rem vertical sidebar at `>=1024px`, the `<details open>` accordion at `<1024px`) | `web/themes/default/core/admin_sidebar.tpl` (the partial) + the `.admin-sidebar-shell` / `.admin-sidebar` / `.admin-sidebar__details` / `.admin-sidebar__summary` / `.admin-sidebar__nav` / `.admin-sidebar__link` / `.admin-sidebar-content` rules in `web/themes/default/css/theme.css` (#1259). The active link reuses the shared `.sidebar__link[aria-current="page"]` rule from the main app shell so the dark-pill-in-light / brand-orange-in-dark treatment is single-source. |
 | Render the trailing "Back" link on edit-* admin pages (the only surface that calls `new AdminTabs([], …)`) | `web/themes/default/core/admin_tabs.tpl` is the back-link-only partial (it still has a defensive `{foreach}` for legacy themes, but `web/includes/View/AdminTabs.php` only routes here when `$tabs === []`). Page handlers like `admin.edit.ban.php` / `admin.rcon.php` / `admin.email.php` call `new AdminTabs([], $userbank, $theme)` and the partial emits the right-aligned Back anchor (`.admin-tabs__back` in theme.css). |
-| Add or rename an admin-admins advanced-search filter | `web/pages/admin.admins.php` (filter-building loop + active-filter map for pagination) + `web/pages/admin.admins.search.php` (DTO population) + `web/includes/View/AdminAdminsSearchView.php` (`active_filter_*` properties) + `web/themes/default/box_admin_admins_search.tpl` (input + pre-fill). The form is single-submit AND-semantics with a backward-compat shim for legacy `advType=…&advSearch=…` URLs (#1207 ADM-4); cover new filters in `web/tests/integration/AdminAdminsSearchTest.php`. |
+| Add or rename an admin-admins advanced-search filter | `web/pages/admin.admins.php` (filter-building loop + active-filter map for pagination) + `web/pages/admin.admins.search.php` (DTO population + `$active_filter_count` increment for the new slot) + `web/includes/View/AdminAdminsSearchView.php` (`active_filter_*` properties) + `web/themes/default/box_admin_admins_search.tpl` (input + pre-fill). The form is single-submit AND-semantics with a backward-compat shim for legacy `advType=…&advSearch=…` URLs (#1207 ADM-4); cover new filters in `web/tests/integration/AdminAdminsSearchTest.php`. |
+| Wrap a filter `<form>` in a default-collapsed `<details>` disclosure (admin-admins advanced search; the public banlist / commslist filter bars are candidates for the same shape per #1303's notes) | `.filters-details` rules in `web/themes/default/css/theme.css` + reference shape in `web/themes/default/box_admin_admins_search.tpl` (`<details class="card filters-details" {if $has_active_filters}open{/if}>` with a `<summary data-testid="…-toggle">` carrying the title + chevron + optional "N active" count badge). The View carries paired `int $active_filter_count` + `bool $has_active_filters` properties (#1303); the page handler increments the count once per populated value slot, NEVER per match-mode toggle. The disclosure auto-expands on a post-submit paint so the Clear-filters affordance stays one click away. Visual vocabulary mirrors `core/admin_sidebar.tpl`'s mobile `<details open>` accordion (chevron + `prefers-reduced-motion: reduce` override). |
 | Add a shared "1 of these required" badge for an either/or input pair | `web/themes/default/page_submitban.tpl` (`data-required-group="…"` + the inline guard script — vanilla JS `// @ts-check`, blocks submit when both are empty) |
 | Bootstrap (paths, autoload, theme)     | `web/init.php`                                           |
 | Routing (`?p=…&c=…&o=…`)               | `web/includes/page-builder.php` — unrecognised admin `c=…` returns the 404 page slot via `web/pages/page.404.php` + `Sbpp\View\NotFoundView` (#1207 ADM-1) |
diff --git a/web/includes/View/AdminAdminsSearchView.php b/web/includes/View/AdminAdminsSearchView.php
index 8200bae31..e78dd35cd 100644
--- a/web/includes/View/AdminAdminsSearchView.php
+++ b/web/includes/View/AdminAdminsSearchView.php
@@ -39,6 +39,18 @@
  * (admin.admins.search.php) is the only place that knows whether a
  * given $_GET shape came from a modern submit, a legacy
  * `advType=…&advSearch=…` URL, or nothing at all.
+ *
+ * #1303 — collapsible disclosure
+ * ------------------------------
+ * The form is wrapped in a `<details class="card filters-details">`
+ * default-collapsed disclosure so the unfiltered admin list paints
+ * above the fold. `$has_active_filters` (derived from the nine
+ * `active_filter_*` value slots — match-mode toggles don't count
+ * because they always carry a default) drives the `[open]` attribute,
+ * so any post-submit page paints with the form expanded. The chrome
+ * mirrors `core/admin_sidebar.tpl`'s mobile `<details open>` pattern
+ * (chevron + label + `prefers-reduced-motion: reduce` override). The
+ * count badge ("Filters · N active") rides `$active_filter_count`.
  */
 final class AdminAdminsSearchView extends View
 {
@@ -74,6 +86,16 @@ final class AdminAdminsSearchView extends View
      *     to mark the matching `<option selected>` rows.
      * @param list<string> $active_filter_admsrvflag Pre-filled
      *     `admsrvflag[]` values.
+     * @param int $active_filter_count Number of non-empty filter
+     *     value slots — drives the `<summary>` count badge ("Filters
+     *     · N active") and `$has_active_filters`. Match-mode toggles
+     *     (`name_match` / `steam_match` / `admemail_match`) are NOT
+     *     counted: they always carry a default ('0' or '1') and only
+     *     refine the matching filter, they don't filter on their own.
+     * @param bool $has_active_filters Convenience boolean derived from
+     *     `$active_filter_count > 0`. The template uses it to decide
+     *     whether the disclosure paints `<details open>` (post-submit
+     *     paint) vs default-collapsed (first-paint).
      */
     public function __construct(
         public readonly bool $can_editadmin,
@@ -96,6 +118,8 @@ public function __construct(
         public readonly string $active_filter_server = '',
         public readonly array $active_filter_admwebflag = [],
         public readonly array $active_filter_admsrvflag = [],
+        public readonly int $active_filter_count = 0,
+        public readonly bool $has_active_filters = false,
     ) {
     }
 }
diff --git a/web/pages/admin.admins.search.php b/web/pages/admin.admins.search.php
index 82a7481d8..632271211 100644
--- a/web/pages/admin.admins.search.php
+++ b/web/pages/admin.admins.search.php
@@ -178,8 +178,54 @@
     }
 }
 
+// Match-mode defaults differ per filter (#1231):
+//   - steam_match defaults to '0' (exact) — typical SteamID
+//     queries are "find this one admin by their full ID".
+//   - name_match / admemail_match default to '1' (partial) so
+//     pre-#1231 URLs (`?name=alice`) keep their substring
+//     behaviour. Adding the toggle widens the UI without
+//     regressing the default.
+$activeFilterName        = is_string($_GET['name']        ?? null) ? (string) $_GET['name']        : '';
+$activeFilterSteamid     = is_string($_GET['steamid']     ?? null) ? (string) $_GET['steamid']     : '';
+$activeFilterAdmemail    = is_string($_GET['admemail']    ?? null) ? (string) $_GET['admemail']    : '';
+$activeFilterWebgroup    = is_scalar($_GET['webgroup']    ?? null) ? (string) $_GET['webgroup']    : '';
+$activeFilterSrvadmgroup = is_string($_GET['srvadmgroup'] ?? null) ? (string) $_GET['srvadmgroup'] : '';
+$activeFilterSrvgroup    = is_scalar($_GET['srvgroup']    ?? null) ? (string) $_GET['srvgroup']    : '';
+$activeFilterServer      = is_scalar($_GET['server']      ?? null) ? (string) $_GET['server']      : '';
+
+// #1303 — the `admemail` filter is permission-gated by
+// `$can_editadmin` in both the rendering template AND the page
+// handler (`admin.admins.php` ignores `?admemail=` from a user without
+// `EditAdmins | Owner`). For URL-forgery cases where a non-admin
+// passes `?admemail=foo`, the input is hidden in the form and the
+// server narrows nothing; the count must mirror that — otherwise the
+// "N active" badge would say "1 active" while every visible filter
+// row reads empty. Mirror the gate locally so the count stays an
+// honest summary of what the visible form actually filters on.
+$canFilterByEmail = $userbank->HasAccess(WebPermission::mask(WebPermission::EditAdmins, WebPermission::Owner));
+
+// #1303 — count populated filter slots so the disclosure can paint a
+// "Filters · N active" badge on the <summary> and auto-expand on
+// post-submit. Match-mode selects (`name_match` / `steam_match` /
+// `admemail_match`) deliberately don't count: they always carry a
+// default ('0' or '1') and only refine the matching filter, they
+// don't filter on their own. Empty multi-select arrays count as zero
+// even though the array itself "exists" — the user hasn't picked a
+// permission. The `admemail` slot only counts when the user can
+// actually filter by it (see `$canFilterByEmail` above).
+$activeFilterCount =
+      ($activeFilterName        !== '' ? 1 : 0)
+    + ($activeFilterSteamid     !== '' ? 1 : 0)
+    + ($canFilterByEmail && $activeFilterAdmemail !== '' ? 1 : 0)
+    + ($activeFilterWebgroup    !== '' ? 1 : 0)
+    + ($activeFilterSrvadmgroup !== '' ? 1 : 0)
+    + ($activeFilterSrvgroup    !== '' ? 1 : 0)
+    + ($activeFilterServer      !== '' ? 1 : 0)
+    + (count($activeWebFlags) > 0 ? 1 : 0)
+    + (count($activeSrvFlags) > 0 ? 1 : 0);
+
 \Sbpp\View\Renderer::render($theme, new \Sbpp\View\AdminAdminsSearchView(
-    can_editadmin:             $userbank->HasAccess(WebPermission::mask(WebPermission::EditAdmins, WebPermission::Owner)),
+    can_editadmin:             $canFilterByEmail,
     server_list:               $servers,
     server_script:             $serverscript,
     webgroup_list:             $webgroups,
@@ -187,23 +233,18 @@
     srvgroup_list:             $srvgroups,
     admwebflag_list:           $webflag,
     admsrvflag_list:           $serverflag,
-    // Match-mode defaults differ per filter (#1231):
-    //   - steam_match defaults to '0' (exact) — typical SteamID
-    //     queries are "find this one admin by their full ID".
-    //   - name_match / admemail_match default to '1' (partial) so
-    //     pre-#1231 URLs (`?name=alice`) keep their substring
-    //     behaviour. Adding the toggle widens the UI without
-    //     regressing the default.
-    active_filter_name:           is_string($_GET['name']           ?? null) ? (string) $_GET['name']           : '',
+    active_filter_name:           $activeFilterName,
     active_filter_name_match:     is_scalar($_GET['name_match']     ?? null) ? (string) $_GET['name_match']     : '1',
-    active_filter_steamid:        is_string($_GET['steamid']        ?? null) ? (string) $_GET['steamid']        : '',
+    active_filter_steamid:        $activeFilterSteamid,
     active_filter_steam_match:    is_scalar($_GET['steam_match']    ?? null) ? (string) $_GET['steam_match']    : '0',
-    active_filter_admemail:       is_string($_GET['admemail']       ?? null) ? (string) $_GET['admemail']       : '',
+    active_filter_admemail:       $activeFilterAdmemail,
     active_filter_admemail_match: is_scalar($_GET['admemail_match'] ?? null) ? (string) $_GET['admemail_match'] : '1',
-    active_filter_webgroup:       is_scalar($_GET['webgroup']       ?? null) ? (string) $_GET['webgroup']       : '',
-    active_filter_srvadmgroup:    is_string($_GET['srvadmgroup']    ?? null) ? (string) $_GET['srvadmgroup']    : '',
-    active_filter_srvgroup:       is_scalar($_GET['srvgroup']       ?? null) ? (string) $_GET['srvgroup']       : '',
-    active_filter_server:         is_scalar($_GET['server']         ?? null) ? (string) $_GET['server']         : '',
+    active_filter_webgroup:       $activeFilterWebgroup,
+    active_filter_srvadmgroup:    $activeFilterSrvadmgroup,
+    active_filter_srvgroup:       $activeFilterSrvgroup,
+    active_filter_server:         $activeFilterServer,
     active_filter_admwebflag:     $activeWebFlags,
     active_filter_admsrvflag:     $activeSrvFlags,
+    active_filter_count:          $activeFilterCount,
+    has_active_filters:           $activeFilterCount > 0,
 ));
diff --git a/web/tests/e2e/pages/admin/AdminAdmins.ts b/web/tests/e2e/pages/admin/AdminAdmins.ts
index 6ed84183f..ac954c2c8 100644
--- a/web/tests/e2e/pages/admin/AdminAdmins.ts
+++ b/web/tests/e2e/pages/admin/AdminAdmins.ts
@@ -74,6 +74,21 @@ export class AdminAdminsPage extends BasePage {
         return this.page.locator('[data-testid="search-admins-reset"]');
     }
 
+    /** #1303 — the `<details>` disclosure wrapping the search form. */
+    get searchDisclosure(): Locator {
+        return this.page.locator('[data-testid="search-admins-disclosure"]');
+    }
+
+    /** #1303 — the `<summary>` toggle that opens / closes the disclosure. */
+    get searchToggle(): Locator {
+        return this.page.locator('[data-testid="search-admins-toggle"]');
+    }
+
+    /** #1303 — the "N active" badge (only present when count > 0). */
+    get searchActiveCount(): Locator {
+        return this.page.locator('[data-testid="search-admins-active-count"]');
+    }
+
     /** ADM-4 — pre-filled inputs by name. */
     searchInput(field: 'name' | 'steamid' | 'admemail' | 'webgroup' | 'srvadmgroup' | 'srvgroup' | 'admwebflag' | 'admsrvflag' | 'server'): Locator {
         return this.page.locator(`[data-testid="search-admins-${field}"]`);
diff --git a/web/tests/e2e/specs/flows/admin-admins-density.spec.ts b/web/tests/e2e/specs/flows/admin-admins-density.spec.ts
index 2c21403d9..042a3b82b 100644
--- a/web/tests/e2e/specs/flows/admin-admins-density.spec.ts
+++ b/web/tests/e2e/specs/flows/admin-admins-density.spec.ts
@@ -102,9 +102,11 @@ test.describe('flow: admin/admins density rework (#1207 ADM-3, ADM-4 / #1275)',
         const p = new AdminAdminsPage(page);
         await p.goto();
 
-        // Exactly one Search submit + one reset link, sitting at the
-        // bottom of the form (collapsing 8 per-row buttons was the
-        // headline of ADM-4).
+        // Exactly one Search submit + one reset link in the rendered
+        // DOM (collapsing 8 per-row buttons was the headline of
+        // ADM-4). Count assertion works whether the #1303 disclosure
+        // is open or closed — browsers parse <details> children
+        // either way.
         await expect(p.searchSubmit).toHaveCount(1);
         await expect(p.searchReset).toHaveCount(1);
 
@@ -115,6 +117,12 @@ test.describe('flow: admin/admins density rework (#1207 ADM-3, ADM-4 / #1275)',
         const baselineCount = await p.adminRows.count();
         expect(baselineCount).toBeGreaterThanOrEqual(1);
 
+        // #1303 — the form ships inside a default-collapsed
+        // `<details>` disclosure, so open it before driving the
+        // inputs. Native `<details>` makes `[open]` flip
+        // synchronously on click; no animation-driven sentinel.
+        await p.searchToggle.click();
+
         // Two filters at once: a deliberately not-matching login
         // ("zzznoadminmatchesthis") + a steam_match=1 (partial). The
         // login filter narrows the result list to zero — locking the
diff --git a/web/tests/e2e/specs/flows/admin-admins-search-disclosure.spec.ts b/web/tests/e2e/specs/flows/admin-admins-search-disclosure.spec.ts
new file mode 100644
index 000000000..f767f71da
--- /dev/null
+++ b/web/tests/e2e/specs/flows/admin-admins-search-disclosure.spec.ts
@@ -0,0 +1,130 @@
+/**
+ * #1303 — admin/admins advanced-search collapsible disclosure.
+ *
+ * Pre-#1303 the advanced-search card always rendered fully expanded
+ * above the admin list, pushing the actual list well below the fold.
+ * #1303 wraps the form in a `<details class="card filters-details">`
+ * disclosure that:
+ *
+ *   1. **Defaults to collapsed** — bare `?p=admin&c=admins` paints
+ *      `<details>` (no `[open]`) so the unfiltered list is the first
+ *      thing the user sees.
+ *   2. **Auto-expands** when any filter slot is populated — post-submit
+ *      paints `<details open>` so the form chrome (and the
+ *      Clear-filters affordance) remain visible while the user iterates.
+ *   3. **Surfaces an "N active" badge** on the `<summary>` so users can
+ *      see at a glance how narrow the current filter set is even while
+ *      the disclosure is collapsed.
+ *
+ * Selector contract: every assertion anchors on the `data-testid`
+ * hooks (`search-admins-disclosure`, `search-admins-toggle`,
+ * `search-admins-active-count`) — never CSS class chains, never
+ * visible text as the primary selector. The `<details>` toggle is a
+ * native HTML control so we use `evaluate(el => el.hasAttribute(...))`
+ * to read the open state (Playwright doesn't ship a "details open"
+ * helper); the assertion is single-instant, no `setTimeout` needed.
+ *
+ * Server-side AND-semantics + the count's per-slot definition are
+ * covered in the PHPUnit `AdminAdminsSearchTest` (see
+ * `testDisclosureCountMatchesPopulatedFilterSlots` and friends). This
+ * spec only locks the BROWSER chrome — that the disclosure exists,
+ * defaults closed, opens on click, and re-paints opened on a deep
+ * link with active filters.
+ */
+
+import { expect, test } from '../../fixtures/auth.ts';
+import { AdminAdminsPage } from '../../pages/admin/AdminAdmins.ts';
+
+test.describe('flow: admin/admins advanced-search disclosure (#1303)', () => {
+    test('defaults to collapsed on a bare visit', async ({ page }, testInfo) => {
+        test.skip(testInfo.project.name !== 'chromium', 'Disclosure chrome is project-agnostic; pinning to desktop for runtime.');
+
+        const p = new AdminAdminsPage(page);
+        await p.goto();
+        await expect(p.pageMounted).toBeVisible();
+
+        // The disclosure is in the DOM and visible (the toggle paints
+        // even when closed). The form body is rendered (browser keeps
+        // it in the DOM even when `<details>` is closed) but visually
+        // hidden by the native disclosure mechanism.
+        await expect(p.searchDisclosure).toBeVisible();
+        await expect(p.searchToggle).toBeVisible();
+
+        const isOpen = await p.searchDisclosure.evaluate((el) => (el as HTMLDetailsElement).open);
+        expect(isOpen).toBe(false);
+
+        // No filter populated → no "N active" badge.
+        await expect(p.searchActiveCount).toHaveCount(0);
+
+        // The form body still renders inside the closed `<details>`
+        // (the browser keeps it parsed); the submit input is just
+        // hidden by the native disclosure. The Submit element is
+        // therefore in the DOM but `toBeVisible` would (correctly)
+        // report false because it's inside a closed `<details>`.
+        await expect(p.searchSubmit).toHaveCount(1);
+    });
+
+    test('opens on toggle click', async ({ page }, testInfo) => {
+        test.skip(testInfo.project.name !== 'chromium', 'Disclosure chrome is project-agnostic; pinning to desktop for runtime.');
+
+        const p = new AdminAdminsPage(page);
+        await p.goto();
+        await expect(p.pageMounted).toBeVisible();
+
+        // Click the summary — native `<details>` opens. The `[open]`
+        // attribute flip is synchronous so we can read it back
+        // without waiting on any animation-driven sentinel.
+        await p.searchToggle.click();
+        const isOpen = await p.searchDisclosure.evaluate((el) => (el as HTMLDetailsElement).open);
+        expect(isOpen).toBe(true);
+
+        // Form fields become reachable post-toggle (the submit was
+        // hidden inside the closed disclosure on first paint).
+        await expect(p.searchSubmit).toBeVisible();
+        await expect(p.searchInput('name')).toBeVisible();
+    });
+
+    test('auto-expands when navigated to a URL with active filters', async ({ page }, testInfo) => {
+        test.skip(testInfo.project.name !== 'chromium', 'Disclosure chrome is project-agnostic; pinning to desktop for runtime.');
+
+        // Deep-link with `?name=admin` — the page handler computes
+        // `has_active_filters=true` and the template emits
+        // `<details open>`. Mirrors the post-submit paint shape.
+        await page.goto('/index.php?p=admin&c=admins&section=admins&name=admin');
+        const p = new AdminAdminsPage(page);
+        await expect(p.pageMounted).toBeVisible();
+
+        const isOpen = await p.searchDisclosure.evaluate((el) => (el as HTMLDetailsElement).open);
+        expect(isOpen).toBe(true);
+
+        // The "N active" badge surfaces with the right copy.
+        await expect(p.searchActiveCount).toBeVisible();
+        await expect(p.searchActiveCount).toContainText('1 active');
+
+        // Form fields are visible because the disclosure is open.
+        await expect(p.searchInput('name')).toHaveValue('admin');
+        await expect(p.searchSubmit).toBeVisible();
+    });
+
+    test('auto-expand survives multi-filter URLs and the badge tracks the populated count', async ({ page }, testInfo) => {
+        test.skip(testInfo.project.name !== 'chromium', 'Count badge contract is project-agnostic; pinning to desktop for runtime.');
+
+        // Three populated value slots: `name`, `steamid`, `webgroup`.
+        // `name_match` / `steam_match` are refinements on `name` /
+        // `steamid` and must NOT lift the count.
+        await page.goto('/index.php?p=admin&c=admins&section=admins&name=admin&name_match=0&steamid=STEAM_0:0:0&steam_match=1&webgroup=1');
+        const p = new AdminAdminsPage(page);
+        await expect(p.pageMounted).toBeVisible();
+
+        const isOpen = await p.searchDisclosure.evaluate((el) => (el as HTMLDetailsElement).open);
+        expect(isOpen).toBe(true);
+
+        await expect(p.searchActiveCount).toBeVisible();
+        await expect(p.searchActiveCount).toContainText('3 active');
+
+        // The disclosure root carries the same count as a data
+        // attribute so a future fix that drifts the badge from the
+        // computed count fails this assertion immediately.
+        await expect(p.searchDisclosure).toHaveAttribute('data-active-filter-count', '3');
+    });
+});
diff --git a/web/tests/integration/AdminAdminsSearchTest.php b/web/tests/integration/AdminAdminsSearchTest.php
index 972a03a46..1550dc800 100644
--- a/web/tests/integration/AdminAdminsSearchTest.php
+++ b/web/tests/integration/AdminAdminsSearchTest.php
@@ -323,6 +323,160 @@ public function testWebFlagMultiFilterArrayShape(): void
         $this->assertStringContainsString('>charlie<', $html, 'charlie has ADMIN_OWNER');
     }
 
+    /**
+     * #1303 — default render is collapsed.
+     *
+     * On a bare `?p=admin&c=admins` (no filter populated) the
+     * advanced-search disclosure must paint *closed* so the unfiltered
+     * admin list reaches above the fold. The contract is
+     * `<details data-testid="search-admins-disclosure">` WITHOUT the
+     * `open` attribute. We anchor on the testid + the absence of the
+     * `[open]` attribute on that exact element rather than scanning
+     * for the substring "open" anywhere in the document (every
+     * `<details open>` in unrelated chrome would false-positive).
+     */
+    public function testDisclosureClosedByDefault(): void
+    {
+        $_GET = ['p' => 'admin', 'c' => 'admins'];
+
+        $html = $this->renderAdminsPage();
+
+        $disclosure = $this->extractDisclosureTag($html);
+        $this->assertStringNotContainsString(' open', $disclosure, 'default render must be collapsed');
+
+        // The "N active" badge must NOT render when no filter is
+        // populated — verifies the `{if $active_filter_count > 0}`
+        // gate in the template.
+        $this->assertStringNotContainsString('search-admins-active-count', $html);
+
+        // The active-filter count attribute reads zero on the
+        // disclosure root (drives the auto-open + the badge).
+        $this->assertStringContainsString('data-active-filter-count="0"', $disclosure);
+    }
+
+    /**
+     * #1303 — disclosure auto-expands when ANY filter is populated.
+     *
+     * Post-submit (or anyone landing on a deep-linked URL) the form
+     * paints `<details open>` so the filter chrome AND the
+     * Clear-filters link stay visible — without this, the user can't
+     * tell what narrowed the list and the only escape hatch (Clear)
+     * is hidden behind another click.
+     */
+    public function testDisclosureAutoExpandsWithActiveFilter(): void
+    {
+        $_GET = ['p' => 'admin', 'c' => 'admins', 'name' => 'alice'];
+
+        $html = $this->renderAdminsPage();
+
+        $disclosure = $this->extractDisclosureTag($html);
+        $this->assertStringContainsString(' open', $disclosure, 'disclosure must auto-open when a filter is active');
+        $this->assertStringContainsString('data-active-filter-count="1"', $disclosure);
+
+        // Count badge present, with the right value baked into the
+        // aria-label.
+        $this->assertStringContainsString('search-admins-active-count', $html);
+        $this->assertStringContainsString('aria-label="1 active filter"', $html);
+        $this->assertStringContainsString('1 active', $html);
+    }
+
+    /**
+     * #1303 — multi-filter URLs lift the active count to N. Locks the
+     * counter's behaviour against the headline ADM-4 contract: every
+     * populated value slot counts ONCE, match-mode toggles do NOT.
+     *
+     * Two text filters (`name`, `steamid`) + one select (`webgroup`) +
+     * one multi-select (`admwebflag[]`) → 4 active. The presence of
+     * `name_match=0` (a refinement on the `name` filter) must NOT
+     * lift the count to 5; same for `steam_match=1` on `steamid`.
+     */
+    public function testDisclosureCountMatchesPopulatedFilterSlots(): void
+    {
+        $_GET = [
+            'p'          => 'admin',
+            'c'          => 'admins',
+            'name'       => 'alice',
+            'name_match' => '0',
+            'steamid'    => 'STEAM_0:0:1001',
+            'steam_match' => '1',
+            'webgroup'   => (string) $this->powerGid,
+            'admwebflag' => ['ADMIN_OWNER'],
+        ];
+
+        $html = $this->renderAdminsPage();
+
+        $disclosure = $this->extractDisclosureTag($html);
+        $this->assertStringContainsString(' open', $disclosure);
+        $this->assertStringContainsString('data-active-filter-count="4"', $disclosure);
+        $this->assertStringContainsString('aria-label="4 active filters"', $html);
+    }
+
+    /**
+     * #1303 — empty multi-select arrays must NOT lift the count. The
+     * `admwebflag[]=` shape produces an empty array in `$_GET` when
+     * the user submits without picking any flag (some browsers / form
+     * libraries do this); the count's job is to surface populated
+     * filters, so an empty multi-select counts as zero.
+     *
+     * Bare URL with an empty `admwebflag` array → 0 active.
+     */
+    public function testDisclosureIgnoresEmptyMultiSelectArrays(): void
+    {
+        $_GET = [
+            'p'          => 'admin',
+            'c'          => 'admins',
+            'admwebflag' => [],
+            'admsrvflag' => [],
+        ];
+
+        $html = $this->renderAdminsPage();
+
+        $disclosure = $this->extractDisclosureTag($html);
+        $this->assertStringNotContainsString(' open', $disclosure, 'empty multi-select arrays must not auto-open the disclosure');
+        $this->assertStringContainsString('data-active-filter-count="0"', $disclosure);
+        $this->assertStringNotContainsString('search-admins-active-count', $html);
+    }
+
+    /**
+     * #1303 — the `admemail` slot is permission-gated. The page handler
+     * (`admin.admins.php`) ignores `?admemail=…` from a user who lacks
+     * `EditAdmins | Owner`, AND the search box hides the e-mail input
+     * for the same gate. The active-filter count must mirror both —
+     * otherwise URL forgery (or a stale tab from a permission downgrade)
+     * would paint "1 active" on the disclosure summary while every
+     * visible filter row reads empty, and the disclosure would auto-open
+     * exposing nothing actionable.
+     *
+     * Setup: log in as a user with `ADMIN_LIST_ADMINS` only — they can
+     * reach the admin/admins list but the e-mail filter is invisible
+     * to them. A forged `?admemail=alice` then must NOT lift the count.
+     */
+    public function testDisclosureCountIgnoresPermissionGatedEmailSlot(): void
+    {
+        $listOnlyAid = $this->insertAdmin(
+            'enid',
+            'STEAM_0:0:9101',
+            'enid@example.test',
+            -1,
+            ADMIN_LIST_ADMINS,
+        );
+        $this->loginAs($listOnlyAid);
+
+        $_GET = ['p' => 'admin', 'c' => 'admins', 'admemail' => 'alice'];
+
+        $html = $this->renderAdminsPage();
+
+        $disclosure = $this->extractDisclosureTag($html);
+        $this->assertStringNotContainsString(' open', $disclosure, 'forged admemail must not auto-open the disclosure for a user without EditAdmins | Owner');
+        $this->assertStringContainsString('data-active-filter-count="0"', $disclosure);
+        $this->assertStringNotContainsString('search-admins-active-count', $html);
+
+        // Sanity: the e-mail input row itself is hidden for this user
+        // (the `{if $can_editadmin}` gate in the template), so the
+        // count's silence is consistent with the visible form chrome.
+        $this->assertStringNotContainsString('data-testid="search-admins-admemail"', $html);
+    }
+
     /**
      * Structural invariant for #1275: the Pattern A sidebar must
      * carry every section the current user can reach. The owner
@@ -522,6 +676,22 @@ private function extractAdminCount(string $html): int
         $this->fail('admin-count testid not found in rendered HTML');
     }
 
+    /**
+     * Extract the `<details data-testid="search-admins-disclosure" …>`
+     * opening tag from the rendered HTML. Asserting against this slice
+     * (rather than the whole document) keeps the `[open]` /
+     * `data-active-filter-count` checks scoped to the disclosure root
+     * even when sibling chrome (`<details open>` accordions, etc.)
+     * coexists in the same render.
+     */
+    private function extractDisclosureTag(string $html): string
+    {
+        if (preg_match('/<details[^>]*data-testid="search-admins-disclosure"[^>]*>/', $html, $m)) {
+            return $m[0];
+        }
+        $this->fail('search-admins-disclosure testid not found in rendered HTML');
+    }
+
     private function countAdminRows(string $html): int
     {
         return preg_match_all('/data-testid="admin-row"/', $html);
diff --git a/web/themes/default/box_admin_admins_search.tpl b/web/themes/default/box_admin_admins_search.tpl
index 1e7102b9b..233f0408c 100644
--- a/web/themes/default/box_admin_admins_search.tpl
+++ b/web/themes/default/box_admin_admins_search.tpl
@@ -59,6 +59,9 @@
     per option — same pattern B5 established in page_servers.tpl.
 
     Testability hooks (per #1123 issue body, "search-<scope>-<…>"):
+        data-testid="search-admins-disclosure"     <details> outer wrapper (#1303)
+        data-testid="search-admins-toggle"         <summary> click target  (#1303)
+        data-testid="search-admins-active-count"   "N active" badge        (#1303; only when count > 0)
         data-testid="search-admins-form"           outer form
         data-testid="search-admins-name"           login <input>
         data-testid="search-admins-name-match"     login exact / partial match (#1231)
@@ -74,12 +77,47 @@
         data-testid="search-admins-server"         server <select>
         data-testid="search-admins-submit"         the (one) submit button
         data-testid="search-admins-reset"          reset / clear-filters link
+
+    #1303 — collapsible disclosure
+    ------------------------------
+    The form sits inside a `<details class="card filters-details">`
+    default-collapsed wrapper so the unfiltered admin list paints
+    above the fold. The disclosure auto-opens on a post-submit paint
+    when `$has_active_filters` is true so the filter chrome (and the
+    Clear-filters affordance) stays visible while the user is iterating.
+    The `<summary>` mirrors the visual vocabulary `core/admin_sidebar.tpl`
+    uses for its mobile accordion (label + chevron + 180° rotation
+    on `[open]`, `prefers-reduced-motion: reduce` collapses the
+    transition). The count badge ("Filters · N active") rides
+    `$active_filter_count` from the View — only emitted when N > 0.
 *}
+<details class="card filters-details"
+         data-testid="search-admins-disclosure"
+         data-active-filter-count="{$active_filter_count}"
+         {if $has_active_filters}open{/if}
+         style="margin-top:1rem;margin-bottom:1rem">
+    <summary class="filters-details__summary"
+             data-testid="search-admins-toggle"
+             aria-controls="search-admins-form-body">
+        <span class="filters-details__summary-label">
+            <i data-lucide="filter" style="width:14px;height:14px"></i>
+            <span>Advanced search</span>
+            {if $active_filter_count > 0}
+                <span class="filters-details__count"
+                      data-testid="search-admins-active-count"
+                      aria-label="{$active_filter_count} active filter{if $active_filter_count != 1}s{/if}">
+                    &middot; {$active_filter_count} active
+                </span>
+            {/if}
+        </span>
+        <i data-lucide="chevron-down" class="filters-details__chevron" style="width:14px;height:14px"></i>
+    </summary>
+
 <form method="get"
       action="index.php"
       data-testid="search-admins-form"
-      class="card"
-      style="margin-top:1rem;margin-bottom:1rem">
+      id="search-admins-form-body"
+      class="filters-details__form">
     <input type="hidden" name="p" value="admin">
     <input type="hidden" name="c" value="admins">
     {* #1275 — Pattern A. Carry the active section so the post-submit URL
@@ -88,9 +126,18 @@
        same `admins` slug today but only by coincidence. *}
     <input type="hidden" name="section" value="admins">
 
-    <div class="card__header">
+    {*
+        #1303 — drop the redundant `<h3>Advanced search</h3>` that the
+        pre-disclosure `card__header` carried; the `<summary>` above
+        already paints the title (+ chevron + count badge), so emitting
+        it again here would stack two identical headings the moment a
+        user opens the disclosure. Keep the explanatory paragraph that
+        documents the AND-semantics contract — that's the load-bearing
+        copy the audit (#1207 ADM-4) called out, and it has no analog
+        in the summary.
+    *}
+    <div class="card__header filters-details__header">
         <div>
-            <h3>Advanced search</h3>
             <p>Combine any of the filters below — the server narrows the admin list to rows matching <strong>every</strong> populated filter (AND semantics).</p>
         </div>
     </div>
@@ -286,6 +333,7 @@
         </div>
     </div>
 </form>
+</details>
 
 {*
     LoadServerHost replacement (vanilla, post-#1123 D1).
diff --git a/web/themes/default/css/theme.css b/web/themes/default/css/theme.css
index f550d9747..27102283b 100644
--- a/web/themes/default/css/theme.css
+++ b/web/themes/default/css/theme.css
@@ -589,6 +589,76 @@ html.dark .admin-tabs > [aria-current="page"] { border-bottom-color: var(--brand
   .admin-sidebar-content { min-width: 0; }
 }
 
+/* ---- Collapsible filter card (#1303) ----
+
+   Wraps a filter `<form class="card">` in a `<details>` disclosure so
+   the unfiltered list paints above the fold. Default-collapsed; the
+   page handler emits `<details open>` when any filter slot is
+   populated so a post-submit paint shows the filter chrome (and the
+   Clear-filters affordance) without forcing the user to click again.
+
+   First user (#1303): `box_admin_admins_search.tpl`. The shape is
+   designed to be reusable on the public banlist / commslist filter
+   bars (`page_bans.tpl` / `page_comms.tpl`) when those follow per
+   the issue body's "Notes" section.
+
+   Visual vocabulary mirrors `.admin-sidebar__details` /
+   `.admin-sidebar__chevron` so the disclosure feels native to the
+   admin chrome. The chevron rotates 180° on `[open]`; the
+   `prefers-reduced-motion: reduce` global rule (later in this file)
+   already collapses the transition to ~0ms, so no per-rule override
+   needed here. */
+.filters-details { padding: 0; }
+.filters-details > .filters-details__summary {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 0.5rem;
+  padding: 0.625rem 1rem;
+  font-weight: 600;
+  cursor: pointer;
+  list-style: none;
+  user-select: none;
+  border-radius: inherit;
+}
+.filters-details[open] > .filters-details__summary {
+  border-bottom: 1px solid var(--border);
+  border-radius: var(--radius-xl) var(--radius-xl) 0 0;
+}
+.filters-details__summary::-webkit-details-marker { display: none; }
+.filters-details__summary:hover { background: var(--bg-muted); }
+.filters-details__summary:focus-visible {
+  outline: none;
+  box-shadow: 0 0 0 3px rgb(234 88 12 / 0.15);
+  border-color: var(--brand-500);
+}
+.filters-details__summary-label {
+  display: inline-flex;
+  align-items: center;
+  gap: 0.5rem;
+  flex-wrap: wrap;
+}
+.filters-details__count {
+  font-weight: 500;
+  font-size: var(--fs-xs);
+  color: var(--text-muted);
+}
+.filters-details__chevron {
+  transition: transform .15s ease;
+  color: var(--text-muted);
+  flex-shrink: 0;
+}
+.filters-details[open] .filters-details__chevron { transform: rotate(180deg); }
+.filters-details__form { display: contents; }
+/* The form inside the disclosure paints `display: contents` so the
+   `.card__header` + `.card__body` children inherit the card's grid /
+   spacing as if the form weren't there. The header drops its bottom
+   border because the summary already paints one when [open]. */
+.filters-details__header { border-bottom: none; padding-top: 0.5rem; }
+@media (prefers-reduced-motion: reduce) {
+  .filters-details__chevron { transition: none; }
+}
+
 /* ---- Inputs ---- */
 .input, .select, .textarea {
   width: 100%; height: 2.25rem; padding: 0 0.75rem;