API Reference

frac exports hooks and utilities from @usefractal/frac/web that work across multiple runtimes. See the compatibility matrix below for platform-specific availability.

State Management

Get initial tool input, output and metadata

Persist state across view renders

Context Sync

Sync view UI state with the model for contextual responses

Utilities

Create a Zustand store that automatically syncs with view state

Generate fully typed hooks from your MCP server

User Interface

Get layout and visual environment (theme, safe area)

Get user information (locale, device type)

Get and request view display mode changes

Open a modal portaled outside of the view iframe

Resize the view to an arbitrary size

Actions

Call tools from within a view

Open external links

Send a follow-up message in the conversation

Upload and download files

Set URL for “open in app” button in fullscreen mode in ChatGPT

Advanced

Low-level hook to subscribe to window.openai state values (Apps SDK)

Low-level hook to subscribe to MCP App host context (MCP Apps)

Import

All hooks and utilities are exported from @usefractal/frac/web:

import {
  createStore,
  useCallTool,
  useDisplayMode,
  useFiles,
  useLayout,
  useSetOpenInAppUrl,
  useAppsSdkContext,
  useMcpAppContext,
  useOpenExternal,
  useRequestModal,
  useRequestSize,
  useSendFollowUpMessage,
  useToolInfo,
  useUser,
  useViewState,
} from "@usefractal/frac/web";

Runtime Compatibility

frac supports two runtime environments: Apps SDK (ChatGPT) and MCP Apps (open specification). Most hooks work in both, but some features are platform-specific.

Hook / Feature	Apps SDK	MCP Apps	Notes
useToolInfo	✅	✅
useViewState	✅	⚠️	MCP Apps: polyfilled; state doesn’t persist across view renders
data-llm	✅	⚠️	MCP Apps: polyfilled (same limitation as useViewState)
useCallTool	✅	✅
useSendFollowUpMessage	✅	✅
useOpenExternal	✅	✅
useLayout	✅	✅
useUser	✅	✅
useDisplayMode	✅	✅
useFiles	✅	❌	Apps SDK only
useSetOpenInAppUrl	✅	❌	Apps SDK only
useRequestModal	✅	⚠️	MCP Apps: polyfilled; renders in iframe instead of host modal
useRequestSize	❌	✅	MCP Apps only
useAppsSdkContext	✅	❌	Apps SDK only
useMcpAppContext	❌	✅	MCP Apps only