ui: move get_datetime tool to frontend

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

@@ -59,3 +59,4 @@ export * from './uri-template.constants';
 export * from './url.constants';
 export * from './working-directory.constants';
 export * from './read-media';
+export * from './get-datetime';

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

@@ -56,7 +56,8 @@ import type {
 	AgenticSession,
 	McpServerOverride,
 	MCPToolCall,
-	SettingsConfigType
+	SettingsConfigType,
+	ToolExecutionResult
 } from '$lib/types';
 import type {
 	AgenticFlowCallbacks,
@@ -83,7 +84,7 @@ import type {
 	DatabaseMessageExtraAudioFile,
 	DatabaseMessageExtraImageFile
 } from '$lib/types/database';
-import { getAudioInputFormat, isAbortError } from '$lib/utils';
+import { executeGetDatetimeTool, getAudioInputFormat, isAbortError } from '$lib/utils';
 import { SvelteMap } from 'svelte/reactivity';
 
 function createDefaultSession(): AgenticSession {
@@ -942,18 +943,24 @@ class AgenticStore {
 							if (executionResult.isError) toolSuccess = false;
 						} else if (toolSource === ToolSource.FRONTEND) {
 							const args = this.parseToolArguments(toolCall.function.arguments);
-							const executionResult =
-								toolName === BuiltInTool.READ_MEDIA
-									? await ReadMediaService.executeTool(
-											args,
-											{
-												audio: modelsStore.modelSupportsAudio(effectiveModel),
-												vision: modelsStore.modelSupportsVision(effectiveModel)
-											},
-											signal,
-											conversationsStore.activeConversation?.cwd
-										)
-									: await SandboxService.executeTool(toolName, args, signal);
+
+							let executionResult: ToolExecutionResult;
+
+							if (toolName === BuiltInTool.GET_DATETIME) {
+								executionResult = executeGetDatetimeTool();
+							} else if (toolName === BuiltInTool.READ_MEDIA) {
+								executionResult = await ReadMediaService.executeTool(
+									args,
+									{
+										audio: modelsStore.modelSupportsAudio(effectiveModel),
+										vision: modelsStore.modelSupportsVision(effectiveModel)
+									},
+									signal,
+									conversationsStore.activeConversation?.cwd
+								);
+							} else {
+								executionResult = await SandboxService.executeTool(toolName, args, signal);
+							}
 
 							result = executionResult.content;
 

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

@@ -1,5 +1,6 @@
 import { browser } from '$app/environment';
 import {
+	buildGetDatetimeToolDefinition,
 	buildReadMediaToolDefinition,
 	DISABLED_TOOL_KEYS_LOCALSTORAGE_KEY,
 	HOME_TILDE,
@@ -175,7 +176,7 @@ 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';
+
 // Cryptography utilities
 
 export { uuid } from './uuid';