Repository: ggml-org/llama.cpp
Pull request: Server becomes the source of truth for sampling parameter defaults

*Make sure to read the [contributing guidelines](https://github.com/ggml-org/llama.cpp/blob/master/CONTRIBUTING.md) before submitting a PR*

### Server becomes the source of truth for sampling parameter defaults

Sampling defaults in the webui are now empty strings instead of
hardcoded values duplicated from common.h. Empty means "not sent
in the request" (already handled by hasValue()), so the server
decides. Placeholders show the actual server/preset values via /props.

### Fixes

Fixes the "Custom" badge that never appeared on sampling parameters
because client defaults always matched server defaults. Now any
user-set value that differs from the server is flagged.

Close #18129


Changed files:
filename: tools/server/webui/src/lib/components/app/chat/ChatSettings/ChatSettingsFields.svelte
patch: @@ -5,9 +5,12 @@
 	import Label from '$lib/components/ui/label/label.svelte';
 	import * as Select from '$lib/components/ui/select';
 	import { Textarea } from '$lib/components/ui/textarea';
-	import { SETTING_CONFIG_DEFAULT, SETTING_CONFIG_INFO, SETTINGS_KEYS } from '$lib/constants';
+	import { SETTING_CONFIG_INFO, SETTINGS_KEYS } from '$lib/constants';
 	import { SettingsFieldType } from '$lib/enums/settings';
 	import { settingsStore } from '$lib/stores/settings.svelte';
+	import { serverStore } from '$lib/stores/server.svelte';
+	import { modelsStore, selectedModelName } from '$lib/stores/models.svelte';
+	import { normalizeFloatingPoint } from '$lib/utils/precision';
 	import { ChatSettingsParameterSourceIndicator } from '$lib/components/app';
 	import type { Component } from 'svelte';
 
@@ -20,35 +23,36 @@
 
 	let { fields, localConfig, onConfigChange, onThemeChange }: Props = $props();
 
-	// Helper function to get parameter source info for syncable parameters
-	function getParameterSourceInfo(key: string) {
-		if (!settingsStore.canSyncParameter(key)) {
-			return null;
+	// server sampling defaults for placeholders
+	let sp = $derived.by(() => {
+		if (serverStore.isRouterMode) {
+			const m = selectedModelName();
+			if (m) {
+				const p = modelsStore.getModelProps(m);
+				return (p?.default_generation_settings?.params ?? {}) as Record<string, unknown>;
+			}
 		}
-
-		return settingsStore.getParameterInfo(key);
-	}
+		return (serverStore.defaultParams ?? {}) as Record<string, unknown>;
+	});
 </script>
 
 {#each fields as field (field.key)}
 	<div class="space-y-2">
 		{#if field.type === SettingsFieldType.INPUT}
-			{@const paramInfo = getParameterSourceInfo(field.key)}
 			{@const currentValue = String(localConfig[field.key] ?? '')}
-			{@const propsDefault = paramInfo?.serverDefault}
+			{@const serverDefault = sp[field.key]}
 			{@const isCustomRealTime = (() => {
-				if (!paramInfo || propsDefault === undefined) return false;
+				if (serverDefault == null) return false;
+				if (currentValue === '') return false;
 
-				// Apply same rounding logic for real-time comparison
-				const inputValue = currentValue;
-				const numericInput = parseFloat(inputValue);
+				const numericInput = parseFloat(currentValue);
 				const normalizedInput = !isNaN(numericInput)
 					? Math.round(numericInput * 1000000) / 1000000
-					: inputValue;
+					: currentValue;
 				const normalizedDefault =
-					typeof propsDefault === 'number'
-						? Math.round(propsDefault * 1000000) / 1000000
-						: propsDefault;
+					typeof serverDefault === 'number'
+						? Math.round(serverDefault * 1000000) / 1000000
+						: serverDefault;
 
 				return normalizedInput !== normalizedDefault;
 			})()}
@@ -74,17 +78,17 @@
 						// Update local config immediately for real-time badge feedback
 						onConfigChange(field.key, e.currentTarget.value);
 					}}
-					placeholder={`Default: ${SETTING_CONFIG_DEFAULT[field.key] ?? 'none'}`}
+					placeholder={sp[field.key] != null
+						? `Default: ${normalizeFloatingPoint(sp[field.key])}`
+						: ''}
 					class="w-full {isCustomRealTime ? 'pr-8' : ''}"
 				/>
 				{#if isCustomRealTime}
 					<button
 						type="button"
 						onclick={() => {
 							settingsStore.resetParameterToServerDefault(field.key);
-							// Trigger UI update by calling onConfigChange with the default value
-							const defaultValue = propsDefault ?? SETTING_CONFIG_DEFAULT[field.key];
-							onConfigChange(field.key, String(defaultValue));
+							onConfigChange(field.key, '');
 						}}
 						class="absolute top-1/2 right-2 inline-flex h-5 w-5 -translate-y-1/2 items-center justify-center rounded transition-colors hover:bg-muted"
 						aria-label="Reset to default"
@@ -112,7 +116,7 @@
 				id={field.key}
 				value={String(localConfig[field.key] ?? '')}
 				onchange={(e) => onConfigChange(field.key, e.currentTarget.value)}
-				placeholder={`Default: ${SETTING_CONFIG_DEFAULT[field.key] ?? 'none'}`}
+				placeholder=""
 				class="min-h-[10rem] w-full md:max-w-2xl"
 			/>
 
@@ -140,14 +144,12 @@
 				(opt: { value: string; label: string; icon?: Component }) =>
 					opt.value === localConfig[field.key]
 			)}
-			{@const paramInfo = getParameterSourceInfo(field.key)}
 			{@const currentValue = localConfig[field.key]}
-			{@const propsDefault = paramInfo?.serverDefault}
+			{@const serverDefault = sp[field.key]}
 			{@const isCustomRealTime = (() => {
-				if (!paramInfo || propsDefault === undefined) return false;
-
-				// For select fields, do direct comparison (no rounding needed)
-				return currentValue !== propsDefault;
+				if (serverDefault == null) return false;
+				if (currentValue === '' || currentValue === undefined) return false;
+				return currentValue !== serverDefault;
 			})()}
 
 			<div class="flex items-center gap-2">
@@ -190,9 +192,7 @@
 							type="button"
 							onclick={() => {
 								settingsStore.resetParameterToServerDefault(field.key);
-								// Trigger UI update by calling onConfigChange with the default value
-								const defaultValue = propsDefault ?? SETTING_CONFIG_DEFAULT[field.key];
-								onConfigChange(field.key, String(defaultValue));
+								onConfigChange(field.key, '');
 							}}
 							class="absolute top-1/2 right-8 inline-flex h-5 w-5 -translate-y-1/2 items-center justify-center rounded transition-colors hover:bg-muted"
 							aria-label="Reset to default"

filename: tools/server/webui/src/lib/constants/settings-config.ts
patch: @@ -1,8 +1,8 @@
 import { ColorMode } from '$lib/enums/ui';
 import { Monitor, Moon, Sun } from '@lucide/svelte';
 
-export const SETTING_CONFIG_DEFAULT: Record<string, string | number | boolean> = {
-	// Note: in order not to introduce breaking changes, please keep the same data type (number, string, etc) if you want to change the default value. Do not use null or undefined for default value.
+export const SETTING_CONFIG_DEFAULT: Record<string, string | number | boolean | undefined> = {
+	// Note: in order not to introduce breaking changes, please keep the same data type (number, string, etc) if you want to change the default value.
 	// Do not use nested objects, keep it single level. Prefix the key if you need to group them.
 	apiKey: '',
 	systemMessage: '',
@@ -30,27 +30,30 @@ export const SETTING_CONFIG_DEFAULT: Record<string, string | number | boolean> =
 	agenticMaxToolPreviewLines: 25,
 	showToolCallInProgress: false,
 	alwaysShowAgenticTurns: false,
-	// make sure these default values are in sync with `common.h`
-	samplers: 'top_k;typ_p;top_p;min_p;temperature',
+	// sampling params: empty means "use server default"
+	// the server / preset is the source of truth
+	// empty values are shown as placeholders from /props in the UI
+	// and are NOT sent in API requests, letting the server decide
+	samplers: '',
 	backend_sampling: false,
-	temperature: 0.8,
-	dynatemp_range: 0.0,
-	dynatemp_exponent: 1.0,
-	top_k: 40,
-	top_p: 0.95,
-	min_p: 0.05,
-	xtc_probability: 0.0,
-	xtc_threshold: 0.1,
-	typ_p: 1.0,
-	repeat_last_n: 64,
-	repeat_penalty: 1.0,
-	presence_penalty: 0.0,
-	frequency_penalty: 0.0,
-	dry_multiplier: 0.0,
-	dry_base: 1.75,
-	dry_allowed_length: 2,
-	dry_penalty_last_n: -1,
-	max_tokens: -1,
+	temperature: undefined,
+	dynatemp_range: undefined,
+	dynatemp_exponent: undefined,
+	top_k: undefined,
+	top_p: undefined,
+	min_p: undefined,
+	xtc_probability: undefined,
+	xtc_threshold: undefined,
+	typ_p: undefined,
+	repeat_last_n: undefined,
+	repeat_penalty: undefined,
+	presence_penalty: undefined,
+	frequency_penalty: undefined,
+	dry_multiplier: undefined,
+	dry_base: undefined,
+	dry_allowed_length: undefined,
+	dry_penalty_last_n: undefined,
+	max_tokens: undefined,
 	custom: '', // custom json-stringified object
 	// experimental features
 	pyInterpreterEnabled: false,

filename: tools/server/webui/src/lib/stores/settings.svelte.ts
patch: @@ -289,16 +289,10 @@ class SettingsStore {
 		const serverDefaults = this.getServerDefaults();
 
 		if (serverDefaults[key] !== undefined) {
-			const value = normalizeFloatingPoint(serverDefaults[key]);
-
-			this.config[key as keyof SettingsConfigType] =
-				value as SettingsConfigType[keyof SettingsConfigType];
-		} else {
-			if (key in SETTING_CONFIG_DEFAULT) {
-				const defaultValue = getConfigValue(SETTING_CONFIG_DEFAULT, key);
-
-				setConfigValue(this.config, key, defaultValue);
-			}
+			// sampling param known by server: clear it, let server decide
+			setConfigValue(this.config, key, '');
+		} else if (key in SETTING_CONFIG_DEFAULT) {
+			setConfigValue(this.config, key, getConfigValue(SETTING_CONFIG_DEFAULT, key));
 		}
 
 		this.userOverrides.delete(key);
@@ -319,30 +313,22 @@ class SettingsStore {
 	 */
 	syncWithServerDefaults(): void {
 		const propsDefaults = this.getServerDefaults();
-
-		if (Object.keys(propsDefaults).length === 0) {
-			console.warn('No server defaults available for initialization');
-
-			return;
-		}
+		if (Object.keys(propsDefaults).length === 0) return;
 
 		for (const [key, propsValue] of Object.entries(propsDefaults)) {
 			const currentValue = getConfigValue(this.config, key);
 
 			const normalizedCurrent = normalizeFloatingPoint(currentValue);
 			const normalizedDefault = normalizeFloatingPoint(propsValue);
 
+			// if user value matches server, it's not a real override
 			if (normalizedCurrent === normalizedDefault) {
 				this.userOverrides.delete(key);
-				setConfigValue(this.config, key, propsValue);
-			} else if (!this.userOverrides.has(key)) {
-				setConfigValue(this.config, key, propsValue);
 			}
 		}
 
 		this.saveConfig();
-		console.log('Settings initialized with props defaults:', propsDefaults);
-		console.log('Current user overrides after sync:', Array.from(this.userOverrides));
+		console.log('User overrides after sync:', Array.from(this.userOverrides));
 	}
 
 	/**
@@ -352,19 +338,11 @@ class SettingsStore {
 	 */
 	forceSyncWithServerDefaults(): void {
 		const propsDefaults = this.getServerDefaults();
-		const syncableKeys = ParameterSyncService.getSyncableParameterKeys();
-
-		for (const key of syncableKeys) {
+		for (const key of ParameterSyncService.getSyncableParameterKeys()) {
 			if (propsDefaults[key] !== undefined) {
-				const normalizedValue = normalizeFloatingPoint(propsDefaults[key]);
-
-				setConfigValue(this.config, key, normalizedValue);
-			} else {
-				if (key in SETTING_CONFIG_DEFAULT) {
-					const defaultValue = getConfigValue(SETTING_CONFIG_DEFAULT, key);
-
-					setConfigValue(this.config, key, defaultValue);
-				}
+				setConfigValue(this.config, key, '');
+			} else if (key in SETTING_CONFIG_DEFAULT) {
+				setConfigValue(this.config, key, getConfigValue(SETTING_CONFIG_DEFAULT, key));
 			}
 
 			this.userOverrides.delete(key);

filename: tools/server/webui/src/lib/types/settings.d.ts
patch: @@ -5,7 +5,7 @@ import type { DatabaseMessageExtra } from './database';
 import type { ParameterSource, SyncableParameterType, SettingsFieldType } from '$lib/enums';
 import type { Icon } from '@lucide/svelte';
 
-export type SettingsConfigValue = string | number | boolean;
+export type SettingsConfigValue = string | number | boolean | undefined;
 
 export interface SettingsFieldConfig {
 	key: string;