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Cedar’s mention system allows users to reference specific data, people, or objects in their messages using @ symbols. This provides a natural way to give agents precise context about what the user is referring to.

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State-Based Mentions using useStateBasedMentionProvider

Prerequisite – the state referenced by stateKey must already be registered in Cedar with useCedarState or useRegisterState.
Automatically allows the user to @ mention any registered state items. The state must first be a cedarState. See the Agentic State documentation. 
import { useState } from 'react';
import { useRegisterState, useStateBasedMentionProvider } from 'cedar-os';

function TodoApp() {
	const [todos, setTodos] = useState([
		{ id: 1, text: 'Buy groceries', category: 'shopping' },
		{ id: 2, text: 'Call dentist', category: 'health' },
	]);

	// Register the state
	useRegisterState({
		key: 'todos',
		value: todos,
		setValue: setTodos,
		description: 'Todo items',
	});

	// Enable mentions for todos
	useStateBasedMentionProvider({
		stateKey: 'todos',
		trigger: '@',
		labelField: 'text',
		searchFields: ['text', 'category'],
		description: 'Todo items',
		icon: '📝',
		color: '#3b82f6',
		order: 10, // Control display order of mentioned todos
	});

	return <ChatInput />;
}
This keeps all mentionable data in the unified Cedar store and makes it automatically available to the agent. State-based mention providers take in the following configuration options: 
export interface StateBasedMentionProviderConfig {
	stateKey: string; // What state to allow users to mention
	trigger?: string;
	labelField?: string | ((item: any) => string); // How it should be labelled when mentioned in the chat
	searchFields?: string[]; // What fields the user should be able to type to search for the element
	description?: string;
	icon?: ReactNode;
	color?: string; // Hex color
	order?: number; // Order for display (lower numbers appear first)
	renderMenuItem?: (item: MentionItem) => ReactNode;
	renderEditorItem?: (
		item: MentionItem,
		attrs: Record<string, any>
	) => ReactNode;
	renderContextBadge?: (entry: ContextEntry) => ReactNode;
}

​
Custom Rendering

Customize how mentions appear in different contexts: 
import { useStateBasedMentionProvider } from 'cedar-os';

function CustomRendering() {
	useStateBasedMentionProvider({
		stateKey: 'users',
		trigger: '@',
		label: 'Users',
		icon: '👤',
		getItems: (query) => {
			// ... get items logic
		},
		toContextEntry: (item) => ({
			id: item.id,
			source: 'mention',
			data: item.data,
			metadata: { label: item.label, icon: '👤' },
		}),

		// Custom rendering in the mention menu
		renderMenuItem: (item) => (
			<div className='flex items-center gap-2 p-2'>
				<span className='text-lg'>👤</span>
				<div>
					<div className='font-medium'>{item.label}</div>
					<div className='text-sm text-gray-500'>{item.data.role}</div>
				</div>
			</div>
		),

		// Custom rendering in the editor
		renderEditorItem: (item, attrs) => (
			<span className='bg-blue-100 text-blue-800 px-1 rounded'>
				👤 {item.label}
			</span>
		),

		// Custom rendering in context badges
		renderContextBadge: (entry) => (
			<div className='bg-gray-100 px-2 py-1 rounded text-sm'>
				👤 {entry.metadata?.label}
			</div>
		),
	});

	return <ChatInput />;
}

​
Multiple Mention Types

Support different mention triggers: 
import { useStateBasedMentionProvider } from 'cedar-os';

function MultiMentionChat() {
	const users = [
		{ id: '1', name: 'Alice', role: 'Designer' },
		{ id: '2', name: 'Bob', role: 'Developer' },
	];

	const channels = [
		{ id: '1', name: 'general', topic: 'General discussion' },
		{ id: '2', name: 'dev', topic: 'Development updates' },
	];

	const commands = [
		{ id: '1', name: 'help', description: 'Show help' },
		{ id: '2', name: 'reset', description: 'Reset chat' },
	];

	// @ for users
	useStateBasedMentionProvider({
		stateKey: 'users',
		trigger: '@',
		label: 'Users',
		icon: '👤',
		getItems: (query) => {
			const filtered = query
				? users.filter((u) =>
						u.name.toLowerCase().includes(query.toLowerCase())
				  )
				: users;
			return filtered.map((user) => ({
				id: user.id,
				label: user.name,
				data: user,
				metadata: { icon: '👤' },
			}));
		},
		toContextEntry: (item) => ({
			id: item.id,
			source: 'mention',
			data: item.data,
			metadata: { label: item.label, icon: '👤' },
		}),
	});

	// # for channels/topics
	useStateBasedMentionProvider({
		stateKey: 'channels',
		trigger: '#',
		label: 'Channels',
		icon: '📢',
		getItems: (query) => {
			const filtered = query
				? channels.filter((c) =>
						c.name.toLowerCase().includes(query.toLowerCase())
				  )
				: channels;
			return filtered.map((channel) => ({
				id: channel.id,
				label: channel.name,
				data: channel,
				metadata: { icon: '📢' },
			}));
		},
		toContextEntry: (item) => ({
			id: item.id,
			source: 'mention',
			data: item.data,
			metadata: { label: item.label, icon: '📢' },
		}),
	});

	// / for commands
	useStateBasedMentionProvider({
		stateKey: 'commands',
		trigger: '/',
		label: 'Commands',
		icon: '⚡',
		getItems: (query) => {
			const filtered = query
				? commands.filter((c) =>
						c.name.toLowerCase().includes(query.toLowerCase())
				  )
				: commands;
			return filtered.map((command) => ({
				id: command.id,
				label: command.name,
				data: command,
				metadata: { icon: '⚡' },
			}));
		},
		toContextEntry: (item) => ({
			id: item.id,
			source: 'mention',
			data: item.data,
			metadata: { label: item.label, icon: '⚡' },
		}),
	});

	return <ChatInput />;
}

​
Contextual Mentions

Show different mentions based on context: 
import { useEffect } from 'react';
import { useStateBasedMentionProvider } from 'cedar-os';

function ContextualMentions() {
	const currentPage = useCurrentPage();

	// Conditional mention providers
	useEffect(() => {
		if (currentPage === 'projects') {
			const projects = getProjects();
			useStateBasedMentionProvider({
				stateKey: 'projects',
				trigger: '@',
				label: 'Projects',
				icon: '📁',
				getItems: (query) => {
					const filtered = query
						? projects.filter((p) =>
								p.name.toLowerCase().includes(query.toLowerCase())
						  )
						: projects;
					return filtered.map((project) => ({
						id: project.id,
						label: project.name,
						data: project,
						metadata: { icon: '📁' },
					}));
				},
				toContextEntry: (item) => ({
					id: item.id,
					source: 'mention',
					data: item.data,
					metadata: { label: item.label, icon: '📁' },
				}),
			});
		} else if (currentPage === 'tasks') {
			const tasks = getTasks();
			useStateBasedMentionProvider({
				stateKey: 'tasks',
				trigger: '@',
				label: 'Tasks',
				icon: '✅',
				getItems: (query) => {
					const filtered = query
						? tasks.filter((t) =>
								t.title.toLowerCase().includes(query.toLowerCase())
						  )
						: tasks;
					return filtered.map((task) => ({
						id: task.id,
						label: task.title,
						data: task,
						metadata: { icon: '✅' },
					}));
				},
				toContextEntry: (item) => ({
					id: item.id,
					source: 'mention',
					data: item.data,
					metadata: { label: item.label, icon: '✅' },
				}),
			});
		}
	}, [currentPage]);

	return <ChatInput />;
}

// Mock functions for demonstration
function useCurrentPage() {
	return 'projects'; // or 'tasks'
}

function getProjects() {
	return [
		{ id: '1', name: 'Website Redesign' },
		{ id: '2', name: 'Mobile App' },
	];
}

function getTasks() {
	return [
		{ id: '1', title: 'Review PR #123' },
		{ id: '2', title: 'Update documentation' },
	];
}

​
Ordering Mentions

When you have multiple mention providers or context subscriptions, you can control their display order using the order property. This ensures the most important context appears first in the UI.

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Order Property

The order property (optional) determines the display order of context badges:
  • Lower numbers appear first: order: 1 appears before order: 10
  • Default behavior: Items without an order appear last
  • Applies to both: Mention providers and useSubscribeInputContext

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Example: Prioritized Mentions

import {
	useStateBasedMentionProvider,
	useSubscribeInputContext,
} from 'cedar-os';
import { User, FileText, Tag, Archive } from 'lucide-react';

function PrioritizedMentions() {
	// Current user context - highest priority (order: 1)
	useSubscribeInputContext(currentUser, (user) => ({ currentUser: user }), {
		icon: <User />,
		color: '#8B5CF6',
		order: 1, // Always visible first
	});

	// Active documents - high priority (order: 5)
	useStateBasedMentionProvider({
		stateKey: 'activeDocuments',
		trigger: '@',
		labelField: 'title',
		description: 'Active Documents',
		icon: <FileText />,
		color: '#3B82F6',
		order: 5, // After user, before tags
	});

	// Tags - medium priority (order: 10)
	useStateBasedMentionProvider({
		stateKey: 'tags',
		trigger: '#',
		labelField: 'name',
		description: 'Tags',
		icon: <Tag />,
		color: '#10B981',
		order: 10, // After documents
	});

	// Archived items - low priority (order: 100)
	useStateBasedMentionProvider({
		stateKey: 'archivedItems',
		trigger: '@',
		labelField: 'title',
		description: 'Archived',
		icon: <Archive />,
		color: '#6B7280',
		order: 100, // Appears last
	});

	return <ChatInput />;
}

​
Custom Provider with Order

When using useStateBasedMentionProvider, include order: 
useStateBasedMentionProvider({
	stateKey: 'priority-users',
	trigger: '@',
	order: 10,
});

​
Best Practices for Ordering

  1. Reserve low numbers (1-9) for critical context like user info
  2. Use 10-49 for active/selected items
  3. Use 50-99 for general mentions
  4. Use 100+ for archived or low-priority items
  5. Leave gaps between orders for future additions

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Mention Data in Context

Access mentioned items in your agent context: 
// When user types: "Update the status of @task-123 to completed"
// The agent receives:
{
  message: "Update the status of @task-123 to completed",
  mentions: [
    {
      id: "task-123",
      type: "tasks",
      data: {
        id: "task-123",
        title: "Implement user authentication",
        status: "in-progress",
        assignee: "Alice"
      },
      position: { start: 23, end: 32 }
    }
  ]
}

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Next Steps