diff --git a/.gitignore b/.gitignore
index 2434dcf..a84afb0 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,5 @@
 /.idea/
 __pycache__/
 *.pyc
+
+plugins/lookup/__pycache__/
diff --git a/roles/homarr/README.md b/roles/homarr/README.md
index db0ed4d..1e92cba 100644
--- a/roles/homarr/README.md
+++ b/roles/homarr/README.md
@@ -13,7 +13,7 @@ and customizable application tiles.
   - a local admin user with bcrypt-hashed password
   - OIDC and credentials admin groups with full permissions
   - application tiles defined in `homarr_apps`, auto-laid-out across all
-    three screen sizes
+    three screen sizes via the bundled `homarr_compute_layouts` filter
 - Skips the onboarding wizard so the instance is usable right after deploy
 - Restarts the container via handler when the seed or compose file changes
 
@@ -100,6 +100,53 @@ homarr_apps:
     width: 2
 ```
 
+## Layout filter plugin
+
+The grid-packing algorithm that places tiles on the desktop, tablet
+and mobile layouts lives in `filter_plugins/homarr_layout.py` rather
+than inside the Jinja seed template. This keeps the SQL template
+readable and lets the algorithm be unit-tested in isolation.
+
+The filter is invoked once from `tasks/main.yml`:
+
+```yaml
+- name: Compute Homarr app layouts
+  ansible.builtin.set_fact:
+    homarr_layout: "{{ homarr_apps | homarr_compute_layouts }}"
+```
+
+This produces a `homarr_layout` fact with two keys, both consumed by
+`templates/homarr_seed.sql.j2`:
+
+| Key | Shape | Purpose |
+|---|---|---|
+| `apps` | list, same order as `homarr_apps` | each entry enriched with `desktop`, `tablet`, `mobile` sub-dicts of `{x, y, w, h}` |
+| `section_height` | dict with `desktop`, `tablet`, `mobile` | minimum height of the parent section so all tiles fit |
+
+The filter signature accepts custom column counts if Homarr ever
+changes the breakpoint widths:
+
+```jinja
+{{ homarr_apps | homarr_compute_layouts(desktop_cols=12, tablet_cols=8, mobile_cols=4) }}
+```
+
+To debug a layout without running the full deploy, run the play with
+`-vv` — the `Show computed app layouts` task dumps the full
+`homarr_layout` fact.
+
+### Running the filter tests
+
+The filter is covered by unit tests in
+`filter_plugins/tests/test_homarr_layout.py`:
+
+```bash
+pip install pytest ansible-core
+pytest filter_plugins/tests/
+```
+
+15 tests cover packing, width clamping, height/section-height,
+input validation and custom grid sizes.
+
 ## First login
 
 After the role completes, log in at `{{ homarr_base_url }}` with:
diff --git a/roles/homarr/filter_plugins/homarr_layout.py b/roles/homarr/filter_plugins/homarr_layout.py
new file mode 100644
index 0000000..6650709
--- /dev/null
+++ b/roles/homarr/filter_plugins/homarr_layout.py
@@ -0,0 +1,140 @@
+# -*- coding: utf-8 -*-
+# SPDX-License-Identifier: MIT-0
+
+"""Custom Ansible filter plugin for computing Homarr grid layouts.
+
+The Homarr SQL seed needs item_layout rows for three breakpoints
+(desktop / tablet / mobile). Rather than embedding the packing
+algorithm in Jinja with namespace gymnastics, this filter does the
+computation in Python and hands the seed template a ready-to-render
+data structure.
+
+Usage in tasks:
+
+    - name: Compute Homarr app layouts
+      ansible.builtin.set_fact:
+        homarr_layout: "{{ homarr_apps | homarr_compute_layouts }}"
+
+The result is a dict with two keys:
+
+    apps           — original homarr_apps in order, each enriched with
+                     'desktop', 'tablet', 'mobile' sub-dicts of
+                     {'x', 'y', 'w', 'h'} ready for SQL templating.
+    section_height — dict with 'desktop', 'tablet', 'mobile' keys
+                     giving the minimum height (in grid cells) the
+                     parent section must have to fit all tiles.
+"""
+
+from ansible.errors import AnsibleFilterError
+
+
+def _pack(apps, cols):
+    """Greedy left-to-right packing into a fixed-column grid.
+
+    Width values larger than the grid are clamped to the grid width
+    rather than overflowing — so a tile declared with width=8 still
+    renders on the 6-column tablet grid (as a full-width tile) and on
+    the 2-column mobile grid (as a full-width tile) without breaking
+    the layout.
+
+    Returns (placements, total_height) where placements is a list of
+    {'id', 'x', 'y', 'w', 'h'} dicts, one per input app, in the same
+    order. total_height is the y-coordinate of the bottom of the last
+    occupied row (i.e. max(y + h) across placements).
+    """
+    x = 0
+    y = 0
+    row_h = 0
+    max_y = 0
+    placements = []
+
+    for app in apps:
+        w = min(int(app.get('width', 1)), cols)
+        h = int(app.get('height', 1))
+
+        # Wrap to the next row when the tile would overflow the grid.
+        if x + w > cols:
+            x = 0
+            y += row_h
+            row_h = 0
+
+        placements.append({
+            'id': app['id'],
+            'x': x,
+            'y': y,
+            'w': w,
+            'h': h,
+        })
+
+        x += w
+        if h > row_h:
+            row_h = h
+        if y + h > max_y:
+            max_y = y + h
+
+    return placements, max_y
+
+
+def homarr_compute_layouts(apps, desktop_cols=10, tablet_cols=6,
+                           mobile_cols=2):
+    """Compute responsive layouts for a list of Homarr apps.
+
+    Input validation is intentionally strict — a malformed apps list
+    should fail the play with a clear message rather than produce a
+    broken SQL seed and a silently misconfigured dashboard.
+
+    Note: uniqueness of app ids is NOT checked here. The role's
+    `Validate homarr_apps have unique ids` assert task runs earlier
+    and is the single source of truth for that check.
+    """
+    if not isinstance(apps, list):
+        raise AnsibleFilterError(
+            "homarr_compute_layouts: expected a list of apps, "
+            "got {0}".format(type(apps).__name__)
+        )
+
+    for index, app in enumerate(apps):
+        if not isinstance(app, dict):
+            raise AnsibleFilterError(
+                "homarr_compute_layouts: app at index {0} is not a "
+                "dict (got {1})".format(index, type(app).__name__)
+            )
+        for required in ('id', 'width'):
+            if required not in app:
+                raise AnsibleFilterError(
+                    "homarr_compute_layouts: app at index {0} is "
+                    "missing required key '{1}'".format(index, required)
+                )
+
+    desktop, h_desktop = _pack(apps, desktop_cols)
+    tablet, h_tablet = _pack(apps, tablet_cols)
+    mobile, h_mobile = _pack(apps, mobile_cols)
+
+    enriched = []
+    for src, d, t, m in zip(apps, desktop, tablet, mobile):
+        enriched.append({
+            **src,
+            'desktop': {'x': d['x'], 'y': d['y'], 'w': d['w'], 'h': d['h']},
+            'tablet':  {'x': t['x'], 'y': t['y'], 'w': t['w'], 'h': t['h']},
+            'mobile':  {'x': m['x'], 'y': m['y'], 'w': m['w'], 'h': m['h']},
+        })
+
+    # Floor section height at 1 so the section stays visible even
+    # when homarr_apps is empty.
+    return {
+        'apps': enriched,
+        'section_height': {
+            'desktop': max(h_desktop, 1),
+            'tablet':  max(h_tablet, 1),
+            'mobile':  max(h_mobile, 1),
+        },
+    }
+
+
+class FilterModule(object):
+    """Ansible filter plugin entry point."""
+
+    def filters(self):
+        return {
+            'homarr_compute_layouts': homarr_compute_layouts,
+        }
diff --git a/roles/homarr/filter_plugins/tests/test_homarr_layout.py b/roles/homarr/filter_plugins/tests/test_homarr_layout.py
new file mode 100644
index 0000000..3a49f2b
--- /dev/null
+++ b/roles/homarr/filter_plugins/tests/test_homarr_layout.py
@@ -0,0 +1,178 @@
+# -*- coding: utf-8 -*-
+# SPDX-License-Identifier: MIT-0
+
+"""Unit tests for the homarr_layout filter plugin.
+
+Run from the role root:
+
+    pytest filter_plugins/tests/
+
+Requires `pytest` and `ansible-core` in the environment.
+"""
+
+import os
+import sys
+
+# Make the filter importable without having Ansible auto-discovery in
+# the way (it would only run during a real `ansible-playbook` invocation).
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), '..'))
+
+import pytest  # noqa: E402
+
+from ansible.errors import AnsibleFilterError  # noqa: E402
+from homarr_layout import homarr_compute_layouts  # noqa: E402
+
+
+def _app(app_id, width, height=1):
+    """Build a minimal app dict for tests."""
+    return {
+        'id': app_id,
+        'name': app_id.title(),
+        'icon': 'https://example.com/{0}.png'.format(app_id),
+        'href': 'https://{0}.example.com'.format(app_id),
+        'width': width,
+        'height': height,
+    }
+
+
+# ---------------------------------------------------------------------
+# Happy-path packing
+# ---------------------------------------------------------------------
+
+def test_empty_apps_returns_empty_list_and_min_height():
+    result = homarr_compute_layouts([])
+    assert result['apps'] == []
+    # Even an empty grid keeps section_height >= 1 so the section
+    # renders in the UI.
+    assert result['section_height'] == {
+        'desktop': 1, 'tablet': 1, 'mobile': 1,
+    }
+
+
+def test_single_app_positioned_at_origin_in_all_grids():
+    result = homarr_compute_layouts([_app('a', width=2)])
+    a = result['apps'][0]
+    assert a['desktop'] == {'x': 0, 'y': 0, 'w': 2, 'h': 1}
+    assert a['tablet']  == {'x': 0, 'y': 0, 'w': 2, 'h': 1}
+    assert a['mobile']  == {'x': 0, 'y': 0, 'w': 2, 'h': 1}
+
+
+def test_original_app_keys_are_preserved():
+    apps = [_app('nextcloud', width=2)]
+    apps[0]['description'] = 'Cloud Storage'
+    result = homarr_compute_layouts(apps)
+    a = result['apps'][0]
+    # Original fields survive the layout enrichment.
+    assert a['name'] == 'Nextcloud'
+    assert a['description'] == 'Cloud Storage'
+    assert a['icon'] == 'https://example.com/nextcloud.png'
+
+
+def test_desktop_wraps_after_filling_row():
+    # 5 apps of width 2 fill the 10-col desktop row exactly; 6th wraps.
+    apps = [_app('a{0}'.format(i), width=2) for i in range(6)]
+    result = homarr_compute_layouts(apps)
+    assert result['apps'][4]['desktop'] == {'x': 8, 'y': 0, 'w': 2, 'h': 1}
+    assert result['apps'][5]['desktop'] == {'x': 0, 'y': 1, 'w': 2, 'h': 1}
+
+
+def test_mobile_wraps_after_every_app():
+    # Mobile is only 2 cols wide → every app of width 2 starts a new row.
+    apps = [_app('a{0}'.format(i), width=2) for i in range(3)]
+    result = homarr_compute_layouts(apps)
+    assert [a['mobile']['y'] for a in result['apps']] == [0, 1, 2]
+
+
+# ---------------------------------------------------------------------
+# Width clamping
+# ---------------------------------------------------------------------
+
+def test_width_clamped_per_grid():
+    result = homarr_compute_layouts([_app('big', width=8)])
+    # Desktop has room (8 <= 10), tablet clamps to 6, mobile clamps to 2.
+    a = result['apps'][0]
+    assert a['desktop']['w'] == 8
+    assert a['tablet']['w'] == 6
+    assert a['mobile']['w'] == 2
+
+
+def test_width_larger_than_desktop_still_clamps():
+    # A pathological width=20 still works — it just becomes a full-width
+    # tile on every grid.
+    result = homarr_compute_layouts([_app('huge', width=20)])
+    a = result['apps'][0]
+    assert a['desktop']['w'] == 10
+    assert a['tablet']['w'] == 6
+    assert a['mobile']['w'] == 2
+
+
+# ---------------------------------------------------------------------
+# Height handling
+# ---------------------------------------------------------------------
+
+def test_section_height_grows_with_rows():
+    # 6 apps of width 2 on desktop → 5 in row 1, 1 in row 2.
+    apps = [_app('a{0}'.format(i), width=2) for i in range(6)]
+    result = homarr_compute_layouts(apps)
+    assert result['section_height']['desktop'] == 2
+    # On mobile every app is on its own row.
+    assert result['section_height']['mobile'] == 6
+
+
+def test_tall_app_extends_row_height():
+    apps = [
+        _app('tall', width=2, height=3),
+        _app('short', width=2, height=1),
+    ]
+    result = homarr_compute_layouts(apps)
+    # Both fit in row 0 horizontally, but the section must be 3 tall.
+    assert result['section_height']['desktop'] == 3
+
+
+def test_tall_app_pushes_subsequent_row_down():
+    # tall (h=3) fills full desktop width → next app wraps to y=3.
+    result = homarr_compute_layouts([
+        _app('tall', width=10, height=3),
+        _app('next', width=2, height=1),
+    ])
+    assert result['apps'][1]['desktop'] == {'x': 0, 'y': 3, 'w': 2, 'h': 1}
+
+
+# ---------------------------------------------------------------------
+# Input validation
+# ---------------------------------------------------------------------
+
+def test_rejects_non_list_input():
+    with pytest.raises(AnsibleFilterError, match='expected a list'):
+        homarr_compute_layouts('not a list')
+
+
+def test_rejects_non_dict_entry():
+    with pytest.raises(AnsibleFilterError, match='not a dict'):
+        homarr_compute_layouts(['just a string'])
+
+
+def test_rejects_app_without_id():
+    with pytest.raises(AnsibleFilterError, match="missing required key 'id'"):
+        homarr_compute_layouts([{'name': 'no id', 'width': 2}])
+
+
+def test_rejects_app_without_width():
+    with pytest.raises(AnsibleFilterError,
+                       match="missing required key 'width'"):
+        homarr_compute_layouts([{'id': 'no-width', 'name': 'x'}])
+
+
+# ---------------------------------------------------------------------
+# Configurable grid sizes
+# ---------------------------------------------------------------------
+
+def test_custom_grid_sizes():
+    # If Homarr ever switches to 12-col desktop, the filter still works.
+    result = homarr_compute_layouts(
+        [_app('a', width=4), _app('b', width=4), _app('c', width=4)],
+        desktop_cols=12, tablet_cols=8, mobile_cols=4,
+    )
+    # All three fit in desktop row 0 (4+4+4 = 12).
+    assert [a['desktop']['x'] for a in result['apps']] == [0, 4, 8]
+    assert result['section_height']['desktop'] == 1
diff --git a/roles/homarr/tasks/main.yml b/roles/homarr/tasks/main.yml
index 06488f4..9d00cde 100644
--- a/roles/homarr/tasks/main.yml
+++ b/roles/homarr/tasks/main.yml
@@ -128,7 +128,23 @@
   no_log: true
 
 # =====================================================================
-# 5. SEED DATABASE (only if local admin user does not exist yet)
+# 5. COMPUTE APP LAYOUTS
+# =====================================================================
+# Packing is done by the homarr_compute_layouts filter plugin (Python)
+# rather than inline Jinja, so the seed template stays readable and the
+# packing algorithm can be unit-tested in isolation.
+
+- name: Compute Homarr app layouts
+  ansible.builtin.set_fact:
+    homarr_layout: "{{ homarr_apps | homarr_compute_layouts }}"
+
+- name: Show computed app layouts
+  ansible.builtin.debug:
+    var: homarr_layout
+    verbosity: 1
+
+# =====================================================================
+# 6. SEED DATABASE (only if local admin user does not exist yet)
 # =====================================================================
 
 - name: Check if local admin user exists
diff --git a/roles/homarr/templates/homarr_seed.sql.j2 b/roles/homarr/templates/homarr_seed.sql.j2
index fdb1a2f..1d2526b 100644
--- a/roles/homarr/templates/homarr_seed.sql.j2
+++ b/roles/homarr/templates/homarr_seed.sql.j2
@@ -1,35 +1,13 @@
 {#-
-  Auto-layout packing macro.
+  Homarr database seed.
 
-  Greedy left-to-right packing of apps into a grid with `cols` columns.
-  Returns the list of apps with computed x/y/w/h fields.
-
-  Width is clamped to cols (so an app wider than the grid is downsized
-  rather than overflowing). Height is taken as-is.
+  The packing algorithm previously lived in this template as a Jinja
+  `pack()` macro with from_json/to_json round-trips. It has been
+  extracted to the `homarr_compute_layouts` filter plugin (see
+  filter_plugins/homarr_layout.py) and the result is provided as the
+  `homarr_layout` fact set in tasks/main.yml. This template therefore
+  only renders SQL — no logic.
 -#}
-{%- macro pack(apps, cols) -%}
-  {%- set ns = namespace(x=0, y=0, row_h=0, out=[]) -%}
-  {%- for app in apps -%}
-    {%- set w = [app.width, cols] | min -%}
-    {%- set h = app.height | default(1) -%}
-    {%- if ns.x + w > cols -%}
-      {%- set ns.x = 0 -%}
-      {%- set ns.y = ns.y + ns.row_h -%}
-      {%- set ns.row_h = 0 -%}
-    {%- endif -%}
-    {%- set _ = ns.out.append({'id': app.id, 'x': ns.x, 'y': ns.y, 'w': w, 'h': h}) -%}
-    {%- set ns.x = ns.x + w -%}
-    {%- if h > ns.row_h -%}
-      {%- set ns.row_h = h -%}
-    {%- endif -%}
-  {%- endfor -%}
-  {{- ns.out | to_json -}}
-{%- endmacro -%}
-
-{%- set desktop_layout = pack(homarr_apps, 10) | from_json -%}
-{%- set tablet_layout  = pack(homarr_apps, 6)  | from_json -%}
-{%- set mobile_layout  = pack(homarr_apps, 2)  | from_json -%}
-
 BEGIN TRANSACTION;
 
 -- =====================================================================
@@ -148,11 +126,14 @@ VALUES (
     '{"json": {}}'
 );
 
+-- Section height is sized to fit the computed layout (see
+-- homarr_compute_layouts filter). It grows automatically when more
+-- apps or taller tiles are added.
 INSERT OR REPLACE INTO section_layout (section_id, layout_id, parent_section_id, x_offset, y_offset, width, height)
 VALUES
-    ('section-apps', 'layout-desktop', NULL, 0, 0, 10, 3),
-    ('section-apps', 'layout-tablet', NULL, 0, 0, 6, 4),
-    ('section-apps', 'layout-mobile', NULL, 0, 0, 2, 6);
+    ('section-apps', 'layout-desktop', NULL, 0, 0, 10, {{ homarr_layout.section_height.desktop }}),
+    ('section-apps', 'layout-tablet',  NULL, 0, 0, 6,  {{ homarr_layout.section_height.tablet }}),
+    ('section-apps', 'layout-mobile',  NULL, 0, 0, 2,  {{ homarr_layout.section_height.mobile }});
 
 -- Board permissions
 INSERT OR IGNORE INTO boardGroupPermission (board_id, group_id, permission)
@@ -161,11 +142,11 @@ VALUES
     ('board-default', 'group-credentials-admin', 'full-access');
 
 -- =====================================================================
--- APPS (auto-generated from homarr_apps variable)
+-- APPS (positions pre-computed by homarr_compute_layouts filter)
 -- =====================================================================
 
-{% if homarr_apps | length > 0 %}
-{% for app in homarr_apps %}
+{% for app in homarr_layout.apps %}
+-- {{ app.name }}
 INSERT OR IGNORE INTO app (id, name, description, icon_url, href)
 VALUES (
     'app-{{ app.id }}',
@@ -184,28 +165,11 @@ VALUES (
     '{"json": {}}'
 );
 
-{% endfor %}
-
 INSERT OR REPLACE INTO item_layout (item_id, section_id, layout_id, x_offset, y_offset, width, height)
 VALUES
-{% for entry in desktop_layout %}
-    ('item-{{ entry.id }}', 'section-apps', 'layout-desktop', {{ entry.x }}, {{ entry.y }}, {{ entry.w }}, {{ entry.h }}){% if not loop.last %},{% endif %}
-{% endfor %}
-;
+    ('item-{{ app.id }}', 'section-apps', 'layout-desktop', {{ app.desktop.x }}, {{ app.desktop.y }}, {{ app.desktop.w }}, {{ app.desktop.h }}),
+    ('item-{{ app.id }}', 'section-apps', 'layout-tablet',  {{ app.tablet.x }},  {{ app.tablet.y }},  {{ app.tablet.w }},  {{ app.tablet.h }}),
+    ('item-{{ app.id }}', 'section-apps', 'layout-mobile',  {{ app.mobile.x }},  {{ app.mobile.y }},  {{ app.mobile.w }},  {{ app.mobile.h }});
 
-INSERT OR REPLACE INTO item_layout (item_id, section_id, layout_id, x_offset, y_offset, width, height)
-VALUES
-{% for entry in tablet_layout %}
-    ('item-{{ entry.id }}', 'section-apps', 'layout-tablet', {{ entry.x }}, {{ entry.y }}, {{ entry.w }}, {{ entry.h }}){% if not loop.last %},{% endif %}
 {% endfor %}
-;
-
-INSERT OR REPLACE INTO item_layout (item_id, section_id, layout_id, x_offset, y_offset, width, height)
-VALUES
-{% for entry in mobile_layout %}
-    ('item-{{ entry.id }}', 'section-apps', 'layout-mobile', {{ entry.x }}, {{ entry.y }}, {{ entry.w }}, {{ entry.h }}){% if not loop.last %},{% endif %}
-{% endfor %}
-;
-{% endif %}
-
-COMMIT;
\ No newline at end of file
+COMMIT;