diff --git a/src/lib/components/buttons/DownloadDataButton.svelte b/src/lib/components/buttons/DownloadDataButton.svelte
index 02f8907..b76e8ed 100644
--- a/src/lib/components/buttons/DownloadDataButton.svelte
+++ b/src/lib/components/buttons/DownloadDataButton.svelte
@@ -5,14 +5,19 @@
 
 
 	let {
-		downloadData
+		downloadData,
+		disabled = false,
+		title = ''
 	}: {
 		downloadData: () => void|Promise<void>;
+		disabled?: boolean;
+		title?: string;
 	} = $props();
 
 	let isLoading = $state(false);
 
     async function handleDownloadData(){
+        if (isLoading || disabled) return;
         isLoading = true;
         try {
             await downloadData();
@@ -23,7 +28,7 @@
 
 </script>
 
-<Button onclick={handleDownloadData}>
+<Button onclick={handleDownloadData} disabled={isLoading || disabled} {title}>
 	{#if isLoading}
 		<LoadingIcon class="animate-spin" />
     	Downloading...
diff --git a/src/lib/components/buttons/VisualiseDataButton.svelte b/src/lib/components/buttons/VisualiseDataButton.svelte
index b29e45f..8524ed5 100644
--- a/src/lib/components/buttons/VisualiseDataButton.svelte
+++ b/src/lib/components/buttons/VisualiseDataButton.svelte
@@ -12,10 +12,14 @@
         visualiseTable,
         visualiseChart,
         visualiseMap,
+        disabled = false,
+        title = ''
 	}: {
 		visualiseTable: () => void|Promise<void>;
         visualiseChart: () => void|Promise<void>;
         visualiseMap: () => void|Promise<void>;
+        disabled?: boolean;
+        title?: string;
 	} = $props();
 
 	let isLoading = $state(false);
@@ -34,8 +38,8 @@
 
 
 <DropdownMenu.Root>
-    <DropdownMenu.Trigger disabled={isLoading}>
-        <Button disabled={isLoading}>
+    <DropdownMenu.Trigger disabled={isLoading || disabled}>
+        <Button disabled={isLoading || disabled} {title}>
         {#if isLoading}
             <LoadingIcon class="animate-spin" />
             Executing...
diff --git a/src/lib/components/query-builder/QueryActionBar.svelte b/src/lib/components/query-builder/QueryActionBar.svelte
index b59fd45..21fe4ca 100644
--- a/src/lib/components/query-builder/QueryActionBar.svelte
+++ b/src/lib/components/query-builder/QueryActionBar.svelte
@@ -17,6 +17,7 @@
     import UrlIcon from '@lucide/svelte/icons/link-2';
 	import InfoIcon from '@lucide/svelte/icons/info';
 	import PencilIcon from '@lucide/svelte/icons/pencil';
+	import { settings } from '@/stores/settings';
 	
 
 
@@ -24,6 +25,18 @@
 		queryActions
 	}: { queryActions: QueryActions } = $props();
 
+	/**
+	 * The reason that the active query must not run, or null.
+	 *
+	 * The switch is read here as well. `runBlockReason` reads a snapshot of the
+	 * settings, so without this read the bar keeps its state after the user turns
+	 * the safeguard off on the settings page.
+	 */
+	const blockReason = $derived.by(() => {
+		if (!$settings.requireQueryFilters) return null;
+		return queryActions.runBlockReason?.() ?? null;
+	});
+
 	let showingCacheInfoModal = $state(false);
 
 	function showCacheInfoModal(): void {
@@ -46,7 +59,11 @@
 
 	<div class="query-action-group">
 
-		<DownloadDataButton downloadData={queryActions.downloadData} />
+		<DownloadDataButton
+			downloadData={queryActions.downloadData}
+			disabled={!!blockReason}
+			title={blockReason ?? ''}
+		/>
 
 		{#if queryActions.editQuery}
 			<Button onclick={queryActions.editQuery} title="Edit query">
@@ -54,10 +71,12 @@
 				Edit Query
 			</Button>
 		{:else}
-			<VisualiseDataButton 
+			<VisualiseDataButton
 				visualiseTable={queryActions.visualiseTable}
 				visualiseChart={queryActions.visualiseChart}
 				visualiseMap={queryActions.visualiseMap}
+				disabled={!!blockReason}
+				title={blockReason ?? ''}
 			/>
 		{/if}
 		
diff --git a/src/lib/components/query-builder/QueryActions.ts b/src/lib/components/query-builder/QueryActions.ts
index 90a7109..15fea75 100644
--- a/src/lib/components/query-builder/QueryActions.ts
+++ b/src/lib/components/query-builder/QueryActions.ts
@@ -5,6 +5,7 @@ import { addToast } from '@/stores/toasts';
 import { saveQueryFrom } from '@/stores/saved-queries';
 import { goto } from '$app/navigation';
 import { resolve } from '$app/paths';
+import { runBlockReason } from '@/query/query-guard';
 
 export type ActionCallback = (() => void | Promise<void>) | undefined;
 
@@ -31,6 +32,14 @@ export type QueryActions = {
      * See `buildShareLink`.
      */
     getInstanceRef?: () => InstanceRef | null;
+    /**
+     * The reason that the active query must not run, or null. The action bar
+     * disables the run and download buttons with it, and names the reason.
+     *
+     * The value is a snapshot. A component that must react to a change of the
+     * safeguard switch reads `$settings` beside this call.
+     */
+    runBlockReason?: () => string | null;
 };
 
 /**
@@ -55,6 +64,23 @@ export function getDefaultQueryActions(workspace: QueryWorkspace): QueryActions
         return workspace.activeBlock?.instance ?? null;
     }
 
+    /** The reason that the active query must not run. See {@link runBlockReason}. */
+    function activeRunBlockReason(): string | null {
+        return runBlockReason(QueryWorkspace.getQuery(workspace.activeBlock));
+    }
+
+    /**
+     * True when the safeguard stops this query. The caller must not talk to the
+     * node. A query with no filter reads a whole table.
+     */
+    function isBlocked(query: CompiledQuery): boolean {
+        const reason = runBlockReason(query);
+        if (!reason) return false;
+
+        addToast({ message: reason, type: 'warning' });
+        return true;
+    }
+
     /**
      * The node of the active block, or null with a toast. Every action that talks
      * to a node starts here. A missing node is a normal state: the block can come
@@ -88,6 +114,8 @@ export function getDefaultQueryActions(workspace: QueryWorkspace): QueryActions
             return null;
         }
 
+        if (isBlocked(query)) return null;
+
         const instance = requireInstance();
         if (!instance) return null;
 
@@ -133,6 +161,8 @@ export function getDefaultQueryActions(workspace: QueryWorkspace): QueryActions
             return;
         }
 
+        if (isBlocked(query)) return;
+
         const instance = requireInstance();
         if (!instance) return;
 
@@ -207,7 +237,8 @@ export function getDefaultQueryActions(workspace: QueryWorkspace): QueryActions
         resetQuery,
         saveQuery,
         getInstance,
-        getInstanceRef
+        getInstanceRef,
+        runBlockReason: activeRunBlockReason
     };
 }
 
diff --git a/src/lib/components/query-builder/QueryBuilderParameterBlock.svelte b/src/lib/components/query-builder/QueryBuilderParameterBlock.svelte
index 828a7d7..7d79550 100644
--- a/src/lib/components/query-builder/QueryBuilderParameterBlock.svelte
+++ b/src/lib/components/query-builder/QueryBuilderParameterBlock.svelte
@@ -20,9 +20,12 @@
 	import { addToast } from '@/stores/toasts';
 	import type { QuerySelectionStatus } from '@/query/selection-status';
     import type { QueryActions } from './QueryActions';
-	import { defaultOutputFormat, type QueryDraft } from '@/query/draft';
+	import { compileDraft, defaultOutputFormat, type QueryDraft } from '@/query/draft';
 	import MapPinnedIcon from '@lucide/svelte/icons/map-pinned';
+	import TriangleAlertIcon from '@lucide/svelte/icons/triangle-alert';
 	import XIcon from '@lucide/svelte/icons/x';
+	import { runBlockReason } from '@/query/query-guard';
+	import { settings } from '@/stores/settings';
 	import { describeSelection, type SpatialSelection } from '@/geo/spatial-selection';
 	import { hydrateDraftFromQuery } from '@/query/seed-hydration';
 
@@ -92,6 +95,27 @@
 	let lastEmittedDraftKey = $state('');
 	let lastReceivedDraftKey = $state(initialDraft ? JSON.stringify(initialDraft) : '');
 
+	/**
+	 * The reason that this query must not run, or null. It compiles the draft,
+	 * because a filter with no value compiles to nothing.
+	 *
+	 * The switch is read here as well. `runBlockReason` reads a snapshot of the
+	 * settings, so without this read the warning stays after the user turns the
+	 * safeguard off on the settings page.
+	 */
+	const filterWarning = $derived.by(() => {
+		if (!$settings.requireQueryFilters) return null;
+
+		return runBlockReason(
+			compileDraft({
+				tableName: table_name,
+				selectedFields,
+				outputFormat: selected_output_format,
+				spatialFilter
+			})
+		);
+	});
+
 	const firstVisibleItem = $derived(fields.find((item) => !(item.ref as {hidden: boolean})?.hidden));
 
 	const firstVisibleMatchingItem = $derived.by(() => {
@@ -406,6 +430,13 @@
 		</Dialog.Content>
 	</Dialog.Root>
 
+	{#if filterWarning}
+		<p class="filter-warning">
+			<TriangleAlertIcon size={16} />
+			{filterWarning}
+		</p>
+	{/if}
+
 	{#if spatialFilter}
 		<div class="area-filter">
 			<MapPinnedIcon size={16} />
@@ -435,6 +466,22 @@
 
 <style lang="scss">
 
+	.filter-warning {
+		display: flex;
+		align-items: center;
+		gap: 0.5rem;
+		margin: 0.5rem 0 0;
+		padding: 0.5rem 0.75rem;
+		border: 1px solid var(--destructive);
+		border-radius: var(--radius, 0.5rem);
+		font-size: 0.85rem;
+		color: var(--destructive);
+
+		:global(svg) {
+			flex-shrink: 0;
+		}
+	}
+
 	.area-filter {
 		display: flex;
 		flex-direction: row;
diff --git a/src/lib/components/query-builder/QueryBuilderSelectorBlock.svelte b/src/lib/components/query-builder/QueryBuilderSelectorBlock.svelte
index da572ca..2ad6e3b 100644
--- a/src/lib/components/query-builder/QueryBuilderSelectorBlock.svelte
+++ b/src/lib/components/query-builder/QueryBuilderSelectorBlock.svelte
@@ -19,6 +19,8 @@ add new query blocks, duplicate blocks, close clocks, select active blocks
 	// import CircleDashedIcon from '@lucide/svelte/icons/circle-dashed';
 	import { QueryWorkspace } from './QueryWorkspace.svelte';
 	import type { StoredQuery } from '@/stores/stored-query';
+	import { runBlockReason } from '@/query/query-guard';
+	import { settings } from '@/stores/settings';
 
 	// All state lives in the workspace; this component only reads/acts on it.
 	let { 
@@ -31,6 +33,20 @@ add new query blocks, duplicate blocks, close clocks, select active blocks
 	} = $props();
 
 	const COLUMN_PREVIEW_LIMIT = 3;
+
+	/**
+	 * The reason that a block must not run, or null. The card shows a warning
+	 * triangle with this text.
+	 *
+	 * The switch is read here as well. `runBlockReason` reads a snapshot of the
+	 * settings, so without this read the cards keep the triangle after the user
+	 * turns the safeguard off on the settings page.
+	 */
+	function blockReasonFor(block: StoredQuery): string | null {
+		if (!$settings.requireQueryFilters) return null;
+		return runBlockReason(QueryWorkspace.getQuery(block));
+	}
+
 	let editingBlockId: string | null = $state(null);
 	let editingName = $state('');
 	let isCommittingFromKeyboard: boolean = $state(false);
@@ -138,6 +154,7 @@ add new query blocks, duplicate blocks, close clocks, select active blocks
 			-->
 			{@const instance = workspace.instanceFor(block)}
 			{@const missingUrl = workspace.missingInstanceUrlFor(block)}
+			{@const blockReason = blockReasonFor(block)}
 			<div
 				
 				class="query-block-wrapper"
@@ -256,7 +273,14 @@ add new query blocks, duplicate blocks, close clocks, select active blocks
 							<span class="query-stat" title="Amount of selected columns">
 								{status.columns} columns
 							</span>
-							<span class="query-stat" title="Amount of applied filters">
+							<span
+								class="query-stat filter-stat"
+								class:missing={blockReason}
+								title={blockReason ?? 'Amount of applied filters'}
+							>
+								{#if blockReason}
+									<TriangleAlertIcon size="0.75rem" />
+								{/if}
 								{status.filters}
 								{status.filters == 1 ? 'filter' : 'filters'}
 							</span>
@@ -344,6 +368,17 @@ add new query blocks, duplicate blocks, close clocks, select active blocks
 			}
 		}
 
+		// The filter count of the block. The triangle sits on the text baseline.
+		.filter-stat {
+			display: inline-flex;
+			align-items: center;
+			gap: 0.25rem;
+
+			&.missing {
+				color: IndianRed;
+			}
+		}
+
 		// The node of the block. The dot and the icon sit on the text baseline.
 		.instance-stat {
 			display: inline-flex;
diff --git a/src/lib/components/settings/SettingField.svelte b/src/lib/components/settings/SettingField.svelte
index 322e5d0..d27849a 100644
--- a/src/lib/components/settings/SettingField.svelte
+++ b/src/lib/components/settings/SettingField.svelte
@@ -11,6 +11,7 @@
 	import RotateCcwIcon from '@lucide/svelte/icons/rotate-ccw';
 	import Button from '@/components/buttons/Button.svelte';
 	import { Input } from '@/components/ui/input';
+	import { Checkbox } from '$lib/components/ui/checkbox/index.js';
 	import * as Select from '$lib/components/ui/select/index.js';
 	import {
 		DEFAULT_SETTINGS,
@@ -54,6 +55,15 @@
 		return selectValue;
 	});
 
+	/** The stored value of a boolean setting. */
+	const booleanValue = $derived(stored === true);
+
+	/** The word beside the checkbox. */
+	const booleanLabel = $derived.by(() => {
+		if (booleanValue) return 'On';
+		return 'Off';
+	});
+
 	function onNumberChange(event: Event): void {
 		if (definition.type !== 'number') return;
 
@@ -78,6 +88,10 @@
 	function onSelectChange(value: string): void {
 		setSetting(definition.key, value);
 	}
+
+	function onBooleanChange(value: boolean): void {
+		setSetting(definition.key, value);
+	}
 </script>
 
 <div class="setting-field">
@@ -102,6 +116,11 @@
 					<span class="unit">{definition.unit}</span>
 				{/if}
 			</div>
+		{:else if definition.type === 'boolean'}
+			<div class="boolean">
+				<Checkbox id={inputId} checked={booleanValue} onCheckedChange={onBooleanChange} />
+				<label class="boolean-label" for={inputId}>{booleanLabel}</label>
+			</div>
 		{:else if definition.type === 'select'}
 			<Select.Root type="single" value={selectValue} onValueChange={onSelectChange}>
 				<Select.Trigger id={inputId} class="w-full">{selectLabel}</Select.Trigger>
@@ -164,6 +183,18 @@
 			align-items: center;
 			gap: 0.5rem;
 
+			.boolean {
+				display: flex;
+				align-items: center;
+				gap: 0.5rem;
+				flex: 1;
+
+				.boolean-label {
+					font-size: 0.85rem;
+					color: var(--muted-foreground);
+				}
+			}
+
 			.number {
 				display: flex;
 				align-items: center;
diff --git a/src/lib/query/query-guard.ts b/src/lib/query/query-guard.ts
new file mode 100644
index 0000000..6479626
--- /dev/null
+++ b/src/lib/query/query-guard.ts
@@ -0,0 +1,69 @@
+/**
+ * The filter safeguard of the query workbench.
+ *
+ * Beacon holds large datasets. A query with no filter reads a whole table, so
+ * the workbench blocks it. The user turns the safeguard off on the settings
+ * page, with `requireQueryFilters`.
+ *
+ * The rule reads the compiled query, and not the draft. A draft filter with no
+ * value compiles to nothing (`Utils.parameterFilterTypeToFilter` returns null),
+ * so a count over the draft reports a filter that the server never gets. The
+ * compiled query is also the only state of a block that comes from a share link
+ * or from the JSON editor.
+ */
+import type { AndFilter, CompiledQuery, Filter, OrFilter } from '@/beacon-api/types';
+import { getSettings } from '@/stores/settings';
+
+/** The text that the workbench shows when the safeguard blocks a query. */
+export const NO_FILTER_MESSAGE =
+	'This query has no filters. Add at least one filter, or turn off "Require a filter" in the settings.';
+
+/**
+ * The number of leaf filters of a query. A group (`and` / `or`) contributes its
+ * members, and not itself. Therefore an empty group counts as zero.
+ */
+export function countFilters(query: CompiledQuery | null | undefined): number {
+	return countIn(query?.filters ?? []);
+}
+
+function countIn(filters: Filter[]): number {
+	let total = 0;
+
+	for (const filter of filters) {
+		const group = filter as Partial<AndFilter & OrFilter>;
+
+		if (Array.isArray(group.and)) {
+			total += countIn(group.and);
+		} else if (Array.isArray(group.or)) {
+			total += countIn(group.or);
+		} else {
+			total += 1;
+		}
+	}
+
+	return total;
+}
+
+/** True when a query carries at least one filter. */
+export function hasFilters(query: CompiledQuery | null | undefined): boolean {
+	return countFilters(query) > 0;
+}
+
+/** True while the safeguard is on. The settings page holds the switch. */
+export function isFilterRequired(): boolean {
+	return getSettings().requireQueryFilters;
+}
+
+/**
+ * The reason that a query must not run, or null when it may run.
+ *
+ * A missing query gives null. Such a block has no table or no column yet, and
+ * the caller reports that itself. This function judges a compiled query only.
+ */
+export function runBlockReason(query: CompiledQuery | null | undefined): string | null {
+	if (!query) return null;
+	if (!isFilterRequired()) return null;
+	if (hasFilters(query)) return null;
+
+	return NO_FILTER_MESSAGE;
+}
diff --git a/src/lib/stores/settings.ts b/src/lib/stores/settings.ts
index be66c3b..6f648fa 100644
--- a/src/lib/stores/settings.ts
+++ b/src/lib/stores/settings.ts
@@ -30,6 +30,8 @@ export interface BeaconStudioSettings {
 	// -- query ----------------------------------------------------------------
 	/** The output format of a new query block. */
 	defaultOutputFormat: string;
+	/** Blocks a query with no filters. It stops a read of a whole table. */
+	requireQueryFilters: boolean;
 	/** The cap on result size in cells (rows × columns). It protects the browser. */
 	queryCellLimit: number;
 	/** The number of decoded results that the memory cache holds. */
@@ -69,6 +71,7 @@ export interface BeaconStudioSettings {
 
 export const DEFAULT_SETTINGS: BeaconStudioSettings = {
 	defaultOutputFormat: 'parquet',
+	requireQueryFilters: true,
 	queryCellLimit: 50_000_000,
 	memoryCacheMaxEntries: 4,
 	queryHistoryMax: 100,
@@ -119,6 +122,10 @@ export interface TextSettingDefinition extends BaseDefinition {
 	placeholder?: string;
 }
 
+export interface BooleanSettingDefinition extends BaseDefinition {
+	type: 'boolean';
+}
+
 export interface SelectSettingDefinition extends BaseDefinition {
 	type: 'select';
 	options: Array<{ label: string; value: string }>;
@@ -127,6 +134,7 @@ export interface SelectSettingDefinition extends BaseDefinition {
 export type SettingDefinition =
 	| NumberSettingDefinition
 	| TextSettingDefinition
+	| BooleanSettingDefinition
 	| SelectSettingDefinition;
 
 /** One entry per setting. The settings page builds its form from this list. */
@@ -144,6 +152,14 @@ export const SETTING_DEFINITIONS: SettingDefinition[] = [
 			{ label: 'NetCDF', value: 'netcdf' }
 		]
 	},
+	{
+		key: 'requireQueryFilters',
+		group: 'Queries',
+		type: 'boolean',
+		label: 'Require a filter',
+		description:
+			'Blocks a query with no filters in the workbench. Beacon must not read a whole table.'
+	},
 	{
 		key: 'queryCellLimit',
 		group: 'Queries',
diff --git a/src/routes/visualisations/chart-explorer/+page.svelte b/src/routes/visualisations/chart-explorer/+page.svelte
index 66cacd1..bbd3c71 100644
--- a/src/routes/visualisations/chart-explorer/+page.svelte
+++ b/src/routes/visualisations/chart-explorer/+page.svelte
@@ -15,6 +15,9 @@
 	import PlotTabs from '@/components/plots/PlotTabs.svelte';
 	import { ChartExplorerController } from '@/components/plots/ChartExplorerController.svelte';
 	import { type ChartViewState } from '@/plots/plot-config';
+	import { addToast } from '@/stores/toasts';
+	import { runBlockReason } from '@/query/query-guard';
+	import { settings } from '@/stores/settings';
 
 	const workspace = $state(new QueryWorkspace());
 
@@ -59,9 +62,18 @@
 	const activeInstanceUrl = $derived(workspace.activeInstance?.url ?? null);
 
 	let lastRunKey: string | null = $state(null);
+	/**
+	 * The query that the safeguard stopped last. It keeps the warning to one
+	 * toast: this effect writes `lastRunKey`, which makes it run a second time.
+	 */
+	let lastBlockedKey: string | null = $state(null);
 	/** The block of the last run. A new block brings its own plots. */
 	let lastRunBlockId: string | null = $state(null);
 
+	// The safeguard blocks a query with no filter. It belongs in the run key, so
+	// the query runs after the user turns the safeguard off.
+	const requireFilters = $derived($settings.requireQueryFilters);
+
 	// Re-run only when the selected block, or its compiled query content, actually changes.
 	$effect(() => {
 		const blockId = activeBlockId;
@@ -74,7 +86,24 @@
 			return;
 		}
 
-		const runKey = `${blockId}:${instanceUrl}:${key}`;
+		// The safeguard stops a query with no filter. Show nothing, and run nothing.
+		// The run key stays empty, so a revert of the edit runs the query again.
+		const blocked = runBlockReason(untrack(() => compiledQuery));
+		if (blocked) {
+			const blockedKey = `${blockId}:${instanceUrl}:${key}`;
+			if (blockedKey !== lastBlockedKey) {
+				lastBlockedKey = blockedKey;
+				addToast({ type: 'warning', message: blocked });
+			}
+
+			charts.clearQueryResult();
+			lastRunKey = null;
+			return;
+		}
+
+		lastBlockedKey = null;
+
+		const runKey = `${blockId}:${instanceUrl}:${key}:${requireFilters}`;
 		if (runKey === lastRunKey) return;
 
 		const isSameBlock = blockId === lastRunBlockId;
diff --git a/src/routes/visualisations/map-viewer/+page.svelte b/src/routes/visualisations/map-viewer/+page.svelte
index 548f568..975ec16 100644
--- a/src/routes/visualisations/map-viewer/+page.svelte
+++ b/src/routes/visualisations/map-viewer/+page.svelte
@@ -17,6 +17,9 @@
 	import MapDrawTools from '@/components/visualisation/MapDrawTools.svelte';
 	import { MapViewController } from '@/components/visualisation/MapViewController.svelte';
 	import type { SpatialSelection } from '@/geo/spatial-selection';
+	import { addToast } from '@/stores/toasts';
+	import { runBlockReason } from '@/query/query-guard';
+	import { settings } from '@/stores/settings';
 
 	let mapContainer: HTMLDivElement | null = null;
 
@@ -74,9 +77,18 @@
 	const activeInstanceUrl = $derived(workspace.activeInstance?.url ?? null);
 
 	let lastRunKey: string | null = $state(null);
+	/**
+	 * The query that the safeguard stopped last. It keeps the warning to one
+	 * toast: this effect writes `lastRunKey`, which makes it run a second time.
+	 */
+	let lastBlockedKey: string | null = $state(null);
 	/** The block of the last run. A new block may move the camera; a re-run may not. */
 	let lastRunBlockId: string | null = $state(null);
 
+	// The safeguard blocks a query with no filter. It belongs in the run key, so
+	// the query runs after the user turns the safeguard off.
+	const requireFilters = $derived($settings.requireQueryFilters);
+
 	// Repaint when the Legend changes the palette or the range. The reads below
 	// are the dependencies; the redraw itself rebuilds the colour table.
 	$effect(() => {
@@ -102,7 +114,24 @@
 			return;
 		}
 
-		const runKey = `${blockId}:${instanceUrl}:${key}`;
+		// The safeguard stops a query with no filter. Show nothing, and run nothing.
+		// The run key stays empty, so a revert of the edit runs the query again.
+		const blocked = runBlockReason(untrack(() => compiledQuery));
+		if (blocked) {
+			const blockedKey = `${blockId}:${instanceUrl}:${key}`;
+			if (blockedKey !== lastBlockedKey) {
+				lastBlockedKey = blockedKey;
+				addToast({ type: 'warning', message: blocked });
+			}
+
+			map.clearQueryResult();
+			lastRunKey = null;
+			return;
+		}
+
+		lastBlockedKey = null;
+
+		const runKey = `${blockId}:${instanceUrl}:${key}:${requireFilters}`;
 		if (runKey === lastRunKey) return;
 
 		const isSameBlock = blockId === lastRunBlockId;
diff --git a/src/routes/visualisations/table-explorer/+page.svelte b/src/routes/visualisations/table-explorer/+page.svelte
index 26b7ca9..a92983c 100644
--- a/src/routes/visualisations/table-explorer/+page.svelte
+++ b/src/routes/visualisations/table-explorer/+page.svelte
@@ -17,6 +17,8 @@
 	import { getDefaultQueryActions } from '@/components/query-builder/QueryActions';
 	import VisualisationTabs from '@/components/visualisation/VisualisationTabs.svelte';
 	import { Input } from '@/components/ui/input';
+	import { runBlockReason } from '@/query/query-guard';
+	import { settings } from '@/stores/settings';
 
 	let entry = $state.raw<DatasetEntry | null>(null);
 	let table: ApacheArrow.Table | null = $derived(entry?.table ?? null);
@@ -66,6 +68,15 @@
 	const activeInstanceUrl = $derived(workspace.activeInstance?.url ?? null);
 
 	let lastRunKey: string | null = $state(null);
+	/**
+	 * The query that the safeguard stopped last. It keeps the warning to one
+	 * toast: this effect writes `lastRunKey`, which makes it run a second time.
+	 */
+	let lastBlockedKey: string | null = $state(null);
+
+	// The safeguard blocks a query with no filter. It belongs in the run key, so
+	// the query runs after the user turns the safeguard off.
+	const requireFilters = $derived($settings.requireQueryFilters);
 
 	// The number of the newest run of this page. The store runs one query at a
 	// time, so a new run stops the run in flight. That older run rejects after the
@@ -88,7 +99,28 @@
 			return;
 		}
 
-		const runKey = `${blockId}:${instanceUrl}:${key}`;
+		// The safeguard stops a query with no filter. Show nothing, and run nothing.
+		// The run key stays empty, so a revert of the edit runs the query again.
+		const blocked = runBlockReason(untrack(() => compiledQuery));
+		if (blocked) {
+			const blockedKey = `${blockId}:${instanceUrl}:${key}`;
+			if (blockedKey !== lastBlockedKey) {
+				lastBlockedKey = blockedKey;
+				addToast({ type: 'warning', message: blocked });
+			}
+
+			entry = null;
+			columns = [];
+			displayRows = [];
+			totalRows = 0;
+			isLoading = false;
+			lastRunKey = null;
+			return;
+		}
+
+		lastBlockedKey = null;
+
+		const runKey = `${blockId}:${instanceUrl}:${key}:${requireFilters}`;
 		if (runKey === lastRunKey) return;
 		lastRunKey = runKey;