diff --git a/website/src/lib/components/map/layer-control/extension-api.test.ts b/website/src/lib/components/map/layer-control/extension-api.test.ts
index cf51c0b2e..93afe9050 100644
--- a/website/src/lib/components/map/layer-control/extension-api.test.ts
+++ b/website/src/lib/components/map/layer-control/extension-api.test.ts
@@ -9,6 +9,15 @@ import { ExtensionAPI, type CustomOverlay } from './extension-api';
 import { isSelected } from './utils';
 
 const original = { set: engine.setSetting, delete: engine.deleteSetting };
+
+/** The raster source that an overlay added by an extension uses. */
+function rasterSource(id: string) {
+    const style = overlays[id];
+    assert.ok(typeof style === 'object');
+    const source = style.sources[id];
+    assert.ok(source?.type === 'raster');
+    return source;
+}
 const overlayTreeBefore = JSON.stringify(overlayTree);
 const overlayIdsBefore = Object.keys(overlays).sort();
 
@@ -45,10 +54,7 @@ describe('ExtensionAPI', () => {
     it('adds an overlay as a layer, in the tree of its extension', () => {
         api.addOrUpdateOverlay(overlay('one'));
 
-        const layer = overlays['extension-one'];
-        assert.ok(layer && typeof layer === 'object');
-        const source = (layer as any).sources['extension-one'];
-        assert.equal(source.type, 'raster');
+        const source = rasterSource('extension-one');
         assert.deepEqual(source.tiles, ['https://tiles.example.com/one/{z}/{x}/{y}.png']);
         assert.equal(source.tileSize, 256);
         assert.equal(source.maxzoom, 22);
@@ -69,7 +75,7 @@ describe('ExtensionAPI', () => {
             tileUrls: ['https://tiles.example.com/512/{z}/{x}/{y}.png'],
             maxZoom: 15,
         });
-        const source = (overlays['extension-big'] as any).sources['extension-big'];
+        const source = rasterSource('extension-big');
         assert.equal(source.tileSize, 512);
         assert.equal(source.maxzoom, 15);
     });
@@ -100,9 +106,7 @@ describe('ExtensionAPI', () => {
             tileUrls: ['https://other/{z}'],
         });
         assert.equal(get(api.getLayerName)('extension-one'), 'Renamed');
-        assert.deepEqual((overlays['extension-one'] as any).sources['extension-one'].tiles, [
-            'https://other/{z}',
-        ]);
+        assert.deepEqual(rasterSource('extension-one').tiles, ['https://other/{z}']);
         assert.equal(isSelected(get(settings.currentOverlays)!, 'extension-one'), true);
     });
 
diff --git a/website/src/lib/components/map/map.ts b/website/src/lib/components/map/map.ts
index ed4d80a3f..cc4c97c30 100644
--- a/website/src/lib/components/map/map.ts
+++ b/website/src/lib/components/map/map.ts
@@ -85,15 +85,23 @@ export class MapLibreGLMap {
                         try {
                             const request = `https://nominatim.openstreetmap.org/search?format=json&q=${config.query}&limit=5&accept-language=${language}`;
                             const response = await fetch(request);
-                            const geojson = await response.json();
-                            results.features = geojson.map((result: any) => {
+                            const places: {
+                                lat: string;
+                                lon: string;
+                                type: string;
+                                display_name: string;
+                            }[] = await response.json();
+                            results.features = places.map((result) => {
                                 return {
                                     type: 'Feature',
                                     geometry: {
                                         type: 'Point',
-                                        coordinates: [result.lon, result.lat],
+                                        coordinates: [Number(result.lon), Number(result.lat)],
                                     },
+                                    properties: {},
+                                    text: result.display_name,
                                     place_name: result.display_name,
+                                    place_type: [result.type],
                                 };
                             });
                         } catch {}
diff --git a/website/src/lib/data/layers.ts b/website/src/lib/data/layers.ts
index 83d1aeded..37f22bc36 100644
--- a/website/src/lib/data/layers.ts
+++ b/website/src/lib/data/layers.ts
@@ -1178,6 +1178,25 @@ export type CustomLayer = {
     value: string | StyleSpecification;
 };
 
+/** Whether a saved value is a custom layer, with all that the layers have had from the start. */
+export function isCustomLayer(value: unknown): value is CustomLayer {
+    if (typeof value !== 'object' || value === null) {
+        return false;
+    }
+    const layer: Partial<Record<keyof CustomLayer, unknown>> = value;
+    return (
+        typeof layer.id === 'string' &&
+        typeof layer.name === 'string' &&
+        Array.isArray(layer.tileUrls) &&
+        layer.tileUrls.every((url) => typeof url === 'string') &&
+        typeof layer.maxZoom === 'number' &&
+        (layer.layerType === 'basemap' || layer.layerType === 'overlay') &&
+        (layer.resourceType === 'raster' || layer.resourceType === 'vector') &&
+        (typeof layer.value === 'string' ||
+            (typeof layer.value === 'object' && layer.value !== null))
+    );
+}
+
 type OverpassQueryData = {
     icon: {
         svg: string;
diff --git a/website/src/lib/engine/engine.test.ts b/website/src/lib/engine/engine.test.ts
index a5493a2fa..1a4d13935 100644
--- a/website/src/lib/engine/engine.test.ts
+++ b/website/src/lib/engine/engine.test.ts
@@ -143,19 +143,25 @@ describe('errors', () => {
 });
 
 describe('selection', () => {
+    /** The selected files, when files are selected. */
+    const selectedFiles = () => {
+        const selection = get(engine.selection);
+        return selection.type === 'file' ? selection.fileIds : [];
+    };
+
     it('adds and toggles files', async () => {
         await load('simple', 'with_tracks', 'with_waypoint');
         const [a, b, c] = get(engine.order);
         await engine.select([a]);
         await engine.select([b], 'add');
-        assert.deepEqual(new Set((get(engine.selection) as any).fileIds), new Set([a, b]));
+        assert.deepEqual(new Set(selectedFiles()), new Set([a, b]));
         await engine.select([a], 'toggle');
-        assert.deepEqual((get(engine.selection) as any).fileIds, [b]);
+        assert.deepEqual(selectedFiles(), [b]);
         await engine.select([]);
         assert.deepEqual(get(engine.selection), { type: 'empty' });
 
         assert.equal(await engine.selectAll(), true);
-        assert.deepEqual(new Set((get(engine.selection) as any).fileIds), new Set([a, b, c]));
+        assert.deepEqual(new Set(selectedFiles()), new Set([a, b, c]));
     });
 
     it('selects tracks and segments of a file', async () => {
diff --git a/website/src/lib/i18n/keys.test.ts b/website/src/lib/i18n/keys.test.ts
index 1d878ad5a..074657611 100644
--- a/website/src/lib/i18n/keys.test.ts
+++ b/website/src/lib/i18n/keys.test.ts
@@ -19,18 +19,23 @@ function sources(dir: string): string[] {
     });
 }
 
-function has(dictionary: any, key: string): boolean {
-    let value = dictionary;
+/** The value at a key (`a.b.c`) of a dictionary, `undefined` if there is none. */
+function valueAt(dictionary: object, key: string): unknown {
+    let value: unknown = dictionary;
     for (const part of key.split('.')) {
         if (value === null || typeof value !== 'object' || !(part in value)) {
-            return false;
+            return undefined;
         }
-        value = value[part];
+        value = (value as Record<string, unknown>)[part];
     }
-    return typeof value === 'string';
+    return value;
 }
 
-function keysOf(dictionary: any, prefix = ''): string[] {
+function has(dictionary: object, key: string): boolean {
+    return typeof valueAt(dictionary, key) === 'string';
+}
+
+function keysOf(dictionary: object, prefix = ''): string[] {
     return Object.entries(dictionary).flatMap(([key, value]) =>
         typeof value === 'object' && value !== null
             ? keysOf(value, `${prefix}${key}.`)
@@ -60,7 +65,7 @@ describe('translations', () => {
 
     it('have no empty text in english', () => {
         const empty = keysOf(english).filter((key) => {
-            const value = key.split('.').reduce((v: any, part) => v[part], english);
+            const value = valueAt(english, key);
             return typeof value === 'string' && value.trim() === '';
         });
         assert.deepEqual(empty, []);
diff --git a/website/src/lib/scripts/pwa-manifest.ts b/website/src/lib/scripts/pwa-manifest.ts
index 62dbcf2bd..b611cbd09 100644
--- a/website/src/lib/scripts/pwa-manifest.ts
+++ b/website/src/lib/scripts/pwa-manifest.ts
@@ -1,7 +1,7 @@
 import fs from 'fs';
 import { languages } from '$lib/i18n/languages';
 
-function localizeManifest(manifestTemplateData: any, language: string) {
+function localizeManifest(manifestTemplateData: Record<string, unknown>, language: string) {
     const localizedManifestFile = `static/${language}.manifest.webmanifest`;
     const localizedStringsFile = `src/locales/${language}.json`;
     const localizedStrings = JSON.parse(fs.readFileSync(localizedStringsFile, 'utf8'));
diff --git a/website/src/lib/state/setting.test.ts b/website/src/lib/state/setting.test.ts
index 3b2002c99..3a5e6686a 100644
--- a/website/src/lib/state/setting.test.ts
+++ b/website/src/lib/state/setting.test.ts
@@ -1,13 +1,17 @@
 import assert from 'node:assert/strict';
 import { afterEach, beforeEach, describe, it } from 'node:test';
 import { get } from 'svelte/store';
-import type { LayerTreeType } from '$lib/data/layers';
+import { isCustomLayer, type LayerTreeType } from '$lib/data/layers';
 import {
     filterLayerTree,
     getArrayValidator,
     getLayerTreeValidator,
     getLayerValidator,
+    getListValidator,
+    getRecordValidator,
     getValueValidator,
+    isNumber,
+    isString,
     Setting,
     SettingInitOnFirstRead,
     storedValue,
@@ -48,7 +52,9 @@ describe('validators', () => {
         const validate = getValueValidator(['metric', 'imperial'], 'metric');
         assert.equal(validate('imperial'), 'imperial');
         assert.equal(validate('nautical'), 'metric');
-        assert.equal(validate(undefined as any), 'metric');
+        assert.equal(validate(undefined), 'metric');
+        assert.equal(validate(null), 'metric');
+        assert.equal(validate(3), 'metric');
         const optional = getValueValidator<string | undefined>(['slope', undefined], undefined);
         assert.equal(optional('slope'), 'slope');
         assert.equal(optional('other'), undefined);
@@ -60,6 +66,48 @@ describe('validators', () => {
         assert.deepEqual(validate([]), []);
     });
 
+    it('keeps nothing of a saved value that is not a list', () => {
+        const validate = getArrayValidator(['hr', 'cad', 'power']);
+        for (const saved of [null, 'hr', 3, { 0: 'hr' }]) {
+            assert.deepEqual(validate(saved), []);
+        }
+    });
+
+    it('keeps the items of a list that are what it holds', () => {
+        const validate = getListValidator(isString);
+        assert.deepEqual(validate(['a', 3, null, 'b']), ['a', 'b']);
+        assert.deepEqual(validate('a'), []);
+    });
+
+    it('keeps the entries of a record that are what it holds, else takes the fallback', () => {
+        const fallback = { a: 0.5 };
+        const validate = getRecordValidator(isNumber, fallback);
+        assert.deepEqual(validate({ a: 0.4, b: 'x', c: 1 }), { a: 0.4, c: 1 });
+        for (const saved of [null, 3, ['a'], 'a']) {
+            assert.equal(validate(saved), fallback);
+        }
+    });
+
+    it('recognizes a custom layer', () => {
+        const layer = {
+            id: 'custom-0',
+            name: 'Layer',
+            tileUrls: ['https://tiles/{z}/{x}/{y}.png'],
+            maxZoom: 20,
+            layerType: 'basemap',
+            resourceType: 'raster',
+            value: { version: 8, sources: {}, layers: [] },
+        };
+        assert.ok(isCustomLayer(layer));
+        assert.ok(isCustomLayer({ ...layer, resourceType: 'vector', value: 'https://style.json' }));
+        assert.ok(!isCustomLayer({ ...layer, layerType: 'other' }));
+        assert.ok(!isCustomLayer({ ...layer, tileUrls: [3] }));
+        assert.ok(!isCustomLayer({ ...layer, value: null }));
+        const { name: _name, ...nameless } = layer;
+        assert.ok(!isCustomLayer(nameless));
+        assert.ok(!isCustomLayer(null));
+    });
+
     it('accepts the known layers, and the custom and extension ones', () => {
         const validate = getLayerValidator({ libertyTopo: 'url', osm: 'url' }, 'libertyTopo');
         assert.equal(validate('osm'), 'osm');
@@ -67,6 +115,9 @@ describe('validators', () => {
         assert.equal(validate('extension-some-id'), 'extension-some-id');
         assert.equal(validate('gone'), 'libertyTopo');
         assert.equal(validate('toString'), 'libertyTopo');
+        for (const saved of [null, 3, ['osm'], { id: 'osm' }]) {
+            assert.equal(validate(saved), 'libertyTopo');
+        }
     });
 });
 
@@ -116,12 +167,33 @@ describe('layer trees', () => {
             a: false,
             b: false,
         });
+        // a branch saved for a layer, and values that are not choices
+        assert.deepEqual(filterLayerTree({ world: { a: { x: true }, b: 'yes' } }, allowed).world, {
+            a: true,
+            b: false,
+        });
+    });
+
+    it('takes the defaults when what was saved is not a tree', () => {
+        for (const saved of [null, true, 'world', 3, ['world']]) {
+            assert.deepEqual(filterLayerTree(saved, allowed), allowed);
+        }
+        assert.deepEqual(
+            filterLayerTree({ world: null, old: null, other: [true] }, allowed),
+            allowed
+        );
+    });
+
+    it('does not share its branches with the allowed tree', () => {
+        const filtered = filterLayerTree({}, allowed);
+        (filtered.world as LayerTreeType).a = false;
+        assert.equal((allowed.world as LayerTreeType).a, true);
     });
 });
 
 describe('Setting', () => {
     it('has its initial value until it is connected', () => {
-        const setting = new Setting('key', 'initial');
+        const setting = new Setting('key', 'initial', getValueValidator(['initial'], 'initial'));
         assert.equal(get(setting), 'initial');
         setting.connect({});
         assert.equal(get(setting), 'initial');
@@ -145,6 +217,19 @@ describe('Setting', () => {
         assert.deepEqual(saved, {});
     });
 
+    it('takes a saved boolean or number of the type of its initial value', () => {
+        const flag = new Setting('flag', false);
+        flag.connect({ flag: 'true' });
+        assert.equal(get(flag), true);
+        flag.connect({ flag: '"yes"' });
+        assert.equal(get(flag), false);
+        const size = new SettingInitOnFirstRead('size', 170);
+        size.connect({ size: '240' });
+        assert.equal(get(size), 240);
+        size.connect({ size: 'null' });
+        assert.equal(get(size), 170);
+    });
+
     it('saves what it is set to, when it changes', () => {
         const setting = new Setting('key', 1);
         setting.set(2);
@@ -160,13 +245,17 @@ describe('Setting', () => {
 
     it('always saves objects, which may have been changed in place', () => {
         const value = { a: 1 };
-        const setting = new Setting('key', value);
+        const setting = new Setting('key', value, getRecordValidator(isNumber, value));
         setting.set(value);
         assert.deepEqual(saved, { key: '{"a":1}' });
     });
 
     it('forgets what it saved when it has no value', () => {
-        const setting = new Setting<string | undefined>('key', 'x');
+        const setting = new Setting<string | undefined>(
+            'key',
+            'x',
+            getValueValidator<string | undefined>(['x', undefined], undefined)
+        );
         setting.set(undefined);
         assert.equal(get(setting), undefined);
         assert.ok('key' in saved);
@@ -187,7 +276,11 @@ describe('Setting', () => {
 
 describe('SettingInitOnFirstRead', () => {
     it('has no value until it is connected', () => {
-        const setting = new SettingInitOnFirstRead('key', { a: true });
+        const setting = new SettingInitOnFirstRead(
+            'key',
+            { a: true },
+            getLayerTreeValidator({ a: true })
+        );
         assert.equal(get(setting), undefined);
         setting.connect({});
         assert.deepEqual(get(setting), { a: true });
diff --git a/website/src/lib/state/setting.ts b/website/src/lib/state/setting.ts
index 61cb131a4..ca6234500 100644
--- a/website/src/lib/state/setting.ts
+++ b/website/src/lib/state/setting.ts
@@ -20,7 +20,7 @@ export function useSettingsStorage(newStorage: SettingsStorage | undefined) {
 }
 
 /** Reads the saved value of a setting, `undefined` if there is none or if it cannot be read. */
-export function storedValue(stored: StoredSettings, key: string): { value: any } | undefined {
+export function storedValue(stored: StoredSettings, key: string): { value: unknown } | undefined {
     if (!Object.hasOwn(stored, key)) {
         return undefined;
     }
@@ -41,6 +41,26 @@ function save(key: string, value: unknown) {
     }
 }
 
+/**
+ * Makes a saved value one that the setting can hold: what was saved can be anything (an old
+ * format, a value that is not allowed anymore), the validator checks it.
+ */
+export type Validator<V> = (value: unknown) => V;
+
+/**
+ * The validator of a setting: a boolean or a number can do without one, its saved value is then
+ * checked against the type of its initial value. The other settings say what they can hold: a
+ * string is often one of a few, an object has a shape.
+ */
+type ValidatorArgument<V> = [V] extends [boolean] | [number]
+    ? [validator?: Validator<V>]
+    : [validator: Validator<V>];
+
+/** Keeps a saved value that has the type of the initial one (a boolean or a number). */
+function sameTypeAs<V>(initial: V): Validator<V> {
+    return (value) => (typeof value === typeof initial ? (value as V) : initial);
+}
+
 /**
  * A setting: a store whose value is kept when it changes. `S` is what the store holds, which is
  * `V` or, for a setting that has no value until it is read, `V | undefined`.
@@ -48,9 +68,9 @@ function save(key: string, value: unknown) {
 abstract class SettingBase<V, S extends V | undefined> {
     protected _key: string;
     protected _value: Writable<S>;
-    protected _validator?: (value: V) => V;
+    protected _validator: Validator<V>;
 
-    protected constructor(key: string, initial: S, validator?: (value: V) => V) {
+    protected constructor(key: string, initial: S, validator: Validator<V>) {
         this._key = key;
         this._value = writable(initial);
         this._validator = validator;
@@ -59,7 +79,7 @@ abstract class SettingBase<V, S extends V | undefined> {
     /** The saved value, validated, `undefined` if there is none. */
     protected saved(stored: StoredSettings): { value: V } | undefined {
         const saved = storedValue(stored, this._key);
-        return saved && { value: this._validator ? this._validator(saved.value) : saved.value };
+        return saved && { value: this._validator(saved.value) };
     }
 
     /** Takes the saved value, if there is one. */
@@ -83,8 +103,8 @@ abstract class SettingBase<V, S extends V | undefined> {
 }
 
 export class Setting<V> extends SettingBase<V, V> {
-    constructor(key: string, initial: V, validator?: (value: V) => V) {
-        super(key, initial, validator);
+    constructor(key: string, initial: V, ...[validator]: ValidatorArgument<V>) {
+        super(key, initial, validator ?? sameTypeAs(initial));
     }
 
     connect(stored: StoredSettings) {
@@ -99,8 +119,8 @@ export class Setting<V> extends SettingBase<V, V> {
 export class SettingInitOnFirstRead<V> extends SettingBase<V, V | undefined> {
     private _initial: V;
 
-    constructor(key: string, initial: V, validator?: (value: V) => V) {
-        super(key, undefined, validator);
+    constructor(key: string, initial: V, ...[validator]: ValidatorArgument<V>) {
+        super(key, undefined, validator ?? sameTypeAs(initial));
         this._initial = initial;
     }
 
@@ -114,53 +134,90 @@ export class SettingInitOnFirstRead<V> extends SettingBase<V, V | undefined> {
     }
 }
 
-export function getValueValidator<V>(allowed: V[], fallback: V) {
-    const dict = new Set<V>(allowed);
-    return (value: V) => (dict.has(value) ? value : fallback);
+/** Whether a value is one of the allowed ones. */
+function oneOf<V>(allowed: V[]) {
+    const dict = new Set<unknown>(allowed);
+    return (value: unknown): value is V => dict.has(value);
 }
 
-export function getArrayValidator<V>(allowed: V[]) {
-    const dict = new Set<V>(allowed);
-    return (value: V[]) => value.filter((v) => dict.has(v));
+export function getValueValidator<V>(allowed: V[], fallback: V): Validator<V> {
+    const isAllowed = oneOf(allowed);
+    return (value) => (isAllowed(value) ? value : fallback);
 }
 
-export function getLayerValidator(allowed: Record<string, any>, fallback: string) {
-    return (layer: string) =>
-        Object.hasOwn(allowed, layer) ||
-        layer.startsWith('custom-') ||
-        layer.startsWith('extension-')
+export function isString(value: unknown): value is string {
+    return typeof value === 'string';
+}
+
+export function isNumber(value: unknown): value is number {
+    return typeof value === 'number';
+}
+
+/** Keeps the items of a saved list that are what it holds, in their order; nothing if it is not a list. */
+export function getListValidator<V>(isItem: (value: unknown) => value is V): Validator<V[]> {
+    return (value) => (Array.isArray(value) ? value.filter(isItem) : []);
+}
+
+/** Keeps the allowed values of a list, in their order; nothing if what was saved is not a list. */
+export function getArrayValidator<V>(allowed: V[]): Validator<V[]> {
+    return getListValidator(oneOf(allowed));
+}
+
+/** Keeps the entries of a saved record that are what it holds; `fallback` if it is not a record. */
+export function getRecordValidator<V>(
+    isEntry: (value: unknown) => value is V,
+    fallback: Record<string, V>
+): Validator<Record<string, V>> {
+    return (value) =>
+        isRecord(value)
+            ? Object.fromEntries(
+                  Object.entries(value).filter((entry): entry is [string, V] => isEntry(entry[1]))
+              )
+            : fallback;
+}
+
+export function getLayerValidator(
+    allowed: Record<string, unknown>,
+    fallback: string
+): Validator<string> {
+    return (layer) =>
+        typeof layer === 'string' &&
+        (Object.hasOwn(allowed, layer) ||
+            layer.startsWith('custom-') ||
+            layer.startsWith('extension-'))
             ? layer
             : fallback;
 }
 
-export function filterLayerTree(
-    t: LayerTreeType,
-    allowed: LayerTreeType | undefined
-): LayerTreeType {
+/** Whether a value is a record, which can hold the layers of a tree: an object, not null or a list. */
+function isRecord(value: unknown): value is Record<string, unknown> {
+    return typeof value === 'object' && value !== null && !Array.isArray(value);
+}
+
+/**
+ * The saved tree `t`, with the layers of `allowed`: the choices saved for them are kept, the new
+ * ones have their default, and of the others only the custom and extension layers are kept.
+ */
+export function filterLayerTree(t: unknown, allowed: LayerTreeType | undefined): LayerTreeType {
+    const tree = isRecord(t) ? t : {};
     const filtered: LayerTreeType = {};
     if (allowed) {
         Object.entries(allowed).forEach(([key, value]) => {
-            if (Object.hasOwn(t, key)) {
-                if (typeof value === 'boolean') {
-                    filtered[key] = t[key];
-                } else if (typeof value === 'object') {
-                    filtered[key] = filterLayerTree(
-                        typeof t[key] === 'object' ? t[key] : {},
-                        value
-                    );
-                }
+            const saved = Object.hasOwn(tree, key) ? tree[key] : undefined;
+            if (typeof value === 'boolean') {
+                filtered[key] = typeof saved === 'boolean' ? saved : value;
             } else {
-                filtered[key] = value;
+                filtered[key] = filterLayerTree(saved, value);
             }
         });
     }
-    Object.entries(t).forEach(([key, value]) => {
+    Object.entries(tree).forEach(([key, value]) => {
         if (!Object.hasOwn(filtered, key)) {
             if (typeof value === 'boolean') {
                 if (key.startsWith('custom-') || key.startsWith('extension-')) {
                     filtered[key] = value;
                 }
-            } else if (typeof value === 'object') {
+            } else if (isRecord(value)) {
                 filtered[key] = filterLayerTree(value, undefined);
             }
         }
@@ -168,6 +225,6 @@ export function filterLayerTree(
     return filtered;
 }
 
-export function getLayerTreeValidator(allowed: LayerTreeType) {
-    return (value: LayerTreeType) => filterLayerTree(value, allowed);
+export function getLayerTreeValidator(allowed: LayerTreeType): Validator<LayerTreeType> {
+    return (value) => filterLayerTree(value, allowed);
 }
diff --git a/website/src/lib/state/settings.ts b/website/src/lib/state/settings.ts
index 7904dc778..a67a452ba 100644
--- a/website/src/lib/state/settings.ts
+++ b/website/src/lib/state/settings.ts
@@ -8,8 +8,8 @@ import {
     defaultOverpassQueries,
     defaultOverpassTree,
     defaultTerrainSource,
+    isCustomLayer,
     overpassTree,
-    type CustomLayer,
 } from '$lib/data/layers';
 import { browser } from '$app/environment';
 import type { DistanceUnits, TemperatureUnits, VelocityUnits } from '$lib/units/conversions';
@@ -19,7 +19,11 @@ import {
     getArrayValidator,
     getLayerTreeValidator,
     getLayerValidator,
+    getListValidator,
+    getRecordValidator,
     getValueValidator,
+    isNumber,
+    isString,
     Setting,
     SettingInitOnFirstRead,
     useSettingsStorage,
@@ -136,10 +140,14 @@ export const settings = {
         defaultOverpassTree,
         getLayerTreeValidator(overpassTree)
     ),
-    opacities: new Setting('opacities', defaultOpacities),
-    customLayers: new Setting<Record<string, CustomLayer>>('customLayers', {}),
-    customBasemapOrder: new Setting<string[]>('customBasemapOrder', []),
-    customOverlayOrder: new Setting<string[]>('customOverlayOrder', []),
+    opacities: new Setting(
+        'opacities',
+        defaultOpacities,
+        getRecordValidator(isNumber, defaultOpacities)
+    ),
+    customLayers: new Setting('customLayers', {}, getRecordValidator(isCustomLayer, {})),
+    customBasemapOrder: new Setting('customBasemapOrder', [], getListValidator(isString)),
+    customOverlayOrder: new Setting('customOverlayOrder', [], getListValidator(isString)),
     terrainSource: new Setting<TerrainSource>(
         'terrainSource',
         defaultTerrainSource,
diff --git a/website/src/routes/[[language]]/help/[...guide]/+page.svelte b/website/src/routes/[[language]]/help/[...guide]/+page.svelte
index 4bedb62a4..a2778099c 100644
--- a/website/src/routes/[[language]]/help/[...guide]/+page.svelte
+++ b/website/src/routes/[[language]]/help/[...guide]/+page.svelte
@@ -7,8 +7,12 @@
     import { getURLForLanguage } from '$lib/utils';
     import { ChevronLeft, ChevronRight, PenLine, CornerDownRight } from '@lucide/svelte';
     import { i18n } from '$lib/i18n/i18n.svelte';
+    import type { Component } from 'svelte';
 
-    let { data }: { data: { guideModule: any; guideTitles: Record<string, string> } } = $props();
+    let {
+        data,
+    }: { data: { guideModule: { default: Component }; guideTitles: Record<string, string> } } =
+        $props();
 
     let previousGuide = $derived(getPreviousGuide(page.params.guide ?? ''));
     let nextGuide = $derived(getNextGuide(page.params.guide ?? ''));