ui: move get_datetime tool to frontend (#27255)

* ui: move get_datetime tool to frontend

* clarify docs

* server: drop the now unused ctime include

strftime() and gmtime_r() were the only users, both went away with the
get_datetime tool. Also make the renderer's catch inert: the browser
executor always emits JSON, so a non-JSON result is no longer a date to
display.

---------

Co-authored-by: Pascal <admin@serveurperso.com>

tools/ui/src/lib/components/app/chat/ChatMessages/ChatMessage/ChatMessageToolCall/ChatMessageToolCallBlockGetDatetime.svelte

@@ -33,7 +33,7 @@
 				if (typeof obj.result === 'string') return { dateString: obj.result.trim() };
 			}
 		} catch {
-			return { dateString: toolResultString.trim() };
+			// not JSON - nothing to show
 		}
 
 		return {};

tools/ui/src/lib/constants/built-in-tools.constants.ts

@@ -34,7 +34,7 @@ export const BUILTIN_TOOL_UI: Readonly<Record<BuiltInTool, BuiltinToolUiEntry>>
 		label: 'Search files',
 		source: ToolSource.BUILTIN
 	},
-	[BuiltInTool.GET_DATETIME]: { icon: Clock, label: 'Current time', source: ToolSource.BUILTIN },
+	[BuiltInTool.GET_DATETIME]: { icon: Clock, label: 'Current time', source: ToolSource.FRONTEND },
 	[BuiltInTool.GET_INFO]: { icon: Info, label: 'Runtime info', source: ToolSource.BUILTIN },
 	[BuiltInTool.GREP_SEARCH]: {
 		icon: SearchCode,

tools/ui/src/lib/constants/get-datetime.ts

@@ -0,0 +1,20 @@
+import { BuiltInTool, JsonSchemaType, ToolCallType } from '$lib/enums';
+import type { OpenAIToolDefinition } from '$lib/types';
+
+export const GET_DATETIME_TOOL_NAME = BuiltInTool.GET_DATETIME;
+
+export function buildGetDatetimeToolDefinition(): OpenAIToolDefinition {
+	return {
+		function: {
+			description:
+				'Returns the current local date and time in ISO 8601 format, with the IANA time zone name',
+			name: GET_DATETIME_TOOL_NAME,
+			parameters: {
+				properties: {},
+				required: [],
+				type: JsonSchemaType.OBJECT
+			}
+		},
+		type: ToolCallType.FUNCTION
+	};
+}

tools/ui/src/lib/constants/index.ts

@@ -59,4 +59,5 @@ export * from './uri-template.constants';
 export * from './url.constants';
 export * from './working-directory.constants';
 export * from './read-media';
+export * from './get-datetime';
 export * from './browser-info';

tools/ui/src/lib/stores/agentic.svelte.ts

@@ -84,7 +84,12 @@ import type {
 	DatabaseMessageExtraAudioFile,
 	DatabaseMessageExtraImageFile
 } from '$lib/types/database';
-import { executeBrowserInfoTool, getAudioInputFormat, isAbortError } from '$lib/utils';
+import {
+	executeBrowserInfoTool,
+	executeGetDatetimeTool,
+	getAudioInputFormat,
+	isAbortError
+} from '$lib/utils';
 import { SvelteMap } from 'svelte/reactivity';
 
 function createDefaultSession(): AgenticSession {
@@ -946,7 +951,9 @@ class AgenticStore {
 
 							let executionResult: ToolExecutionResult;
 
-							if (toolName === BuiltInTool.GET_INFO) {
+							if (toolName === BuiltInTool.GET_DATETIME) {
+								executionResult = executeGetDatetimeTool();
+							} else if (toolName === BuiltInTool.GET_INFO) {
 								executionResult = executeBrowserInfoTool();
 							} else if (toolName === BuiltInTool.READ_MEDIA) {
 								executionResult = await ReadMediaService.executeTool(

tools/ui/src/lib/stores/tools.svelte.ts

@@ -1,6 +1,7 @@
 import { browser } from '$app/environment';
 import {
 	buildBrowserInfoToolDefinition,
+	buildGetDatetimeToolDefinition,
 	buildReadMediaToolDefinition,
 	DISABLED_TOOL_KEYS_LOCALSTORAGE_KEY,
 	HOME_TILDE,
@@ -176,7 +177,7 @@ class ToolsStore {
 	}
 
 	get frontendTools(): OpenAIToolDefinition[] {
-		const tools: OpenAIToolDefinition[] = [];
+		const tools: OpenAIToolDefinition[] = [buildGetDatetimeToolDefinition()];
 
 		if (settingsStore.config.jsSandboxEnabled) {
 			tools.push(buildSandboxToolDefinition(!!settingsStore.config.symbolicMathEnabled));

tools/ui/src/lib/utils/get-datetime.ts

@@ -0,0 +1,38 @@
+/**
+ * Frontend executor for the `get_datetime` tool. It runs in the browser, so it
+ * reports the user's own clock and time zone instead of the server's UTC time -
+ * a chat about "tomorrow" means the user's tomorrow, not the host's.
+ *
+ * @see buildGetDatetimeToolDefinition in constants/get-datetime.ts - tool schema sent to the LLM
+ */
+
+import type { ToolExecutionResult } from '$lib/types';
+
+function pad(value: number): string {
+	return String(value).padStart(2, '0');
+}
+
+/** ISO 8601 in local time, e.g. `2026-08-17T14:05:09+02:00` */
+function localIsoString(date: Date): string {
+	// getTimezoneOffset() counts minutes behind UTC, ISO 8601 counts them ahead
+	const offset = -date.getTimezoneOffset();
+	const sign = offset < 0 ? '-' : '+';
+	const absOffset = Math.abs(offset);
+	const day = `${date.getFullYear()}-${pad(date.getMonth() + 1)}-${pad(date.getDate())}`;
+	const time = `${pad(date.getHours())}:${pad(date.getMinutes())}:${pad(date.getSeconds())}`;
+
+	return `${day}T${time}${sign}${pad(Math.floor(absOffset / 60))}:${pad(absOffset % 60)}`;
+}
+
+/** The `result` field keeps the shape the `get_datetime` renderer already reads. */
+export function executeGetDatetimeTool(): ToolExecutionResult {
+	const now = new Date();
+
+	return {
+		content: JSON.stringify({
+			result: localIsoString(now),
+			timezone: Intl.DateTimeFormat().resolvedOptions().timeZone
+		}),
+		isError: false
+	};
+}

tools/ui/src/lib/utils/index.ts

@@ -331,6 +331,9 @@ export { getChatCommands } from './chat-commands';
 // SANDBOX_TOOL_DEFINITION is deprecated; kept for backward compatibility.
 export { buildSandboxToolDefinition, SANDBOX_TOOL_DEFINITION } from './sandbox-tool';
 
+// Frontend `get_datetime` executor (the browser clock, not the server's)
+export { executeGetDatetimeTool } from './get-datetime';
+
 // Browser fallback for the server's get_info tool
 export { executeBrowserInfoTool } from './browser-info';