Expo Data Fetching Agent Skill

Framework (OSS). Use when implementing or debugging ANY network request, API call, or data fetching. Covers fetch API, React Query, SWR, error handling, caching, offline support, and Expo Router data loaders (`useLoaderData`).

6k tokens

context cost

the whole folder, loaded on every use

files

instructions only

copies elsewhere

how many repositories repackaged it

2356

stars on the repo

on the repository, not the skill itself

Install

one command, takes just this skill from the repository

npx skills add https://github.com/expo/skills --skill expo-data-fetching

What comes with it

11 659 bytes besides the instruction

agents/openai.yaml

references/expo-router-loaders.md

references/offline-and-cancellation.md

The instruction itself

16 sections, as written by the author

Expo Networking

You MUST use this skill for ANY networking work including API requests, data fetching, caching, or network debugging.

References

Consult these resources as needed:

references/
  expo-router-loaders.md        Route-level data loading with Expo Router loaders (web, SDK 55+)
  offline-and-cancellation.md   NetInfo network status, offline-first React Query, AbortController

When to Use

Use this skill when:

Implementing API requests
Setting up data fetching (React Query, SWR)
Using Expo Router data loaders (useLoaderData, web SDK 55+)
Debugging network failures
Implementing caching strategies
Handling offline scenarios
Authentication/token management
Configuring API URLs and environment variables

Preferences

Avoid axios, prefer expo/fetch

Common Issues & Solutions

1. Basic Fetch Usage

Simple GET request:

const fetchUser = async (userId: string) => {
  const response = await fetch(`https://api.example.com/users/${userId}`);

  if (!response.ok) {
    throw new Error(`HTTP error! status: ${response.status}`);
  }

  return response.json();
};

POST request with body:

const createUser = async (userData: UserData) => {
  const response = await fetch("https://api.example.com/users", {
    method: "POST",
    headers: {
      "Content-Type": "application/json",
      Authorization: `Bearer ${token}`,
    },
    body: JSON.stringify(userData),
  });

  if (!response.ok) {
    const error = await response.json();
    throw new Error(error.message);
  }

  return response.json();
};

2. React Query (TanStack Query)

Setup:

// app/_layout.tsx
import { QueryClient, QueryClientProvider } from "@tanstack/react-query";

const queryClient = new QueryClient({
  defaultOptions: {
    queries: {
      staleTime: 1000 * 60 * 5, // 5 minutes
      retry: 2,
    },
  },
});

export default function RootLayout() {
  return (
    <QueryClientProvider client={queryClient}>
      <Stack />
    </QueryClientProvider>
  );
}

Fetching data:

import { useQuery } from "@tanstack/react-query";

function UserProfile({ userId }: { userId: string }) {
  const { data, isLoading, error, refetch } = useQuery({
    queryKey: ["user", userId],
    queryFn: () => fetchUser(userId),
  });

  if (isLoading) return <Loading />;
  if (error) return <Error message={error.message} />;

  return <Profile user={data} />;
}

Mutations:

import { useMutation, useQueryClient } from "@tanstack/react-query";

function CreateUserForm() {
  const queryClient = useQueryClient();

  const mutation = useMutation({
    mutationFn: createUser,
    onSuccess: () => {
      // Invalidate and refetch
      queryClient.invalidateQueries({ queryKey: ["users"] });
    },
  });

  const handleSubmit = (data: UserData) => {
    mutation.mutate(data);
  };

  return <Form onSubmit={handleSubmit} isLoading={mutation.isPending} />;
}

3. Error Handling

Comprehensive error handling:

class ApiError extends Error {
  constructor(message: string, public status: number, public code?: string) {
    super(message);
    this.name = "ApiError";
  }
}

const fetchWithErrorHandling = async (url: string, options?: RequestInit) => {
  try {
    const response = await fetch(url, options);

    if (!response.ok) {
      const error = await response.json().catch(() => ({}));
      throw new ApiError(
        error.message || "Request failed",
        response.status,
        error.code
      );
    }

    return response.json();
  } catch (error) {
    if (error instanceof ApiError) {
      throw error;
    }
    // Network error (no internet, timeout, etc.)
    throw new ApiError("Network error", 0, "NETWORK_ERROR");
  }
};

Retry logic:

const fetchWithRetry = async (
  url: string,
  options?: RequestInit,
  retries = 3
) => {
  for (let i = 0; i < retries; i++) {
    try {
      return await fetchWithErrorHandling(url, options);
    } catch (error) {
      if (i === retries - 1) throw error;
      // Exponential backoff
      await new Promise((r) => setTimeout(r, Math.pow(2, i) * 1000));
    }
  }
};

4. Authentication

Token management:

import * as SecureStore from "expo-secure-store";

const TOKEN_KEY = "auth_token";

export const auth = {
  getToken: () => SecureStore.getItemAsync(TOKEN_KEY),
  setToken: (token: string) => SecureStore.setItemAsync(TOKEN_KEY, token),
  removeToken: () => SecureStore.deleteItemAsync(TOKEN_KEY),
};

// Authenticated fetch wrapper
const authFetch = async (url: string, options: RequestInit = {}) => {
  const token = await auth.getToken();

  return fetch(url, {
    ...options,
    headers: {
      ...options.headers,
      Authorization: token ? `Bearer ${token}` : "",
    },
  });
};

Token refresh:

let isRefreshing = false;
let refreshPromise: Promise<string> | null = null;

const getValidToken = async (): Promise<string> => {
  const token = await auth.getToken();

  if (!token || isTokenExpired(token)) {
    if (!isRefreshing) {
      isRefreshing = true;
      refreshPromise = refreshToken().finally(() => {
        isRefreshing = false;
        refreshPromise = null;
      });
    }
    return refreshPromise!;
  }

  return token;
};

5. Offline Support

Network-status detection with NetInfo and offline-first React Query setup: see ./references/offline-and-cancellation.md.

6. Environment Variables

Using environment variables for API configuration:

Expo supports environment variables with the EXPO_PUBLIC_ prefix. These are inlined at build time and available in your JavaScript code.

// .env
EXPO_PUBLIC_API_URL=https://api.example.com
EXPO_PUBLIC_API_VERSION=v1

// Usage in code
const API_URL = process.env.EXPO_PUBLIC_API_URL;

const fetchUsers = async () => {
  const response = await fetch(`${API_URL}/users`);
  return response.json();
};

Environment-specific configuration:

// .env.development
EXPO_PUBLIC_API_URL=http://localhost:3000

// .env.production
EXPO_PUBLIC_API_URL=https://api.production.com

Creating an API client with environment config:

// api/client.ts
const BASE_URL = process.env.EXPO_PUBLIC_API_URL;

if (!BASE_URL) {
  throw new Error("EXPO_PUBLIC_API_URL is not defined");
}

export const apiClient = {
  get: async <T,>(path: string): Promise<T> => {
    const response = await fetch(`${BASE_URL}${path}`);
    if (!response.ok) throw new Error(`HTTP ${response.status}`);
    return response.json();
  },

  post: async <T,>(path: string, body: unknown): Promise<T> => {
    const response = await fetch(`${BASE_URL}${path}`, {
      method: "POST",
      headers: { "Content-Type": "application/json" },
      body: JSON.stringify(body),
    });
    if (!response.ok) throw new Error(`HTTP ${response.status}`);
    return response.json();
  },
};

Important notes:

Only variables prefixed with EXPO_PUBLIC_ are exposed to the client bundle
Never put secrets (API keys with write access, database passwords) in EXPO_PUBLIC_ variables—they're visible in the built app
Environment variables are inlined at build time, not runtime
Restart the dev server after changing .env files
For server-side secrets in API routes, use variables without the EXPO_PUBLIC_ prefix

TypeScript support:

// types/env.d.ts
declare global {
  namespace NodeJS {
    interface ProcessEnv {
      EXPO_PUBLIC_API_URL: string;
      EXPO_PUBLIC_API_VERSION?: string;
    }
  }
}

export {};

7. Request Cancellation

AbortController on unmount (React Query cancels automatically): see ./references/offline-and-cancellation.md.

Decision Tree

User asks about networking
  |-- Route-level data loading (web, SDK 55+)?
  |   \-- Expo Router loaders — see references/expo-router-loaders.md
  |
  |-- Basic fetch?
  |   \-- Use fetch API with error handling
  |
  |-- Need caching/state management?
  |   |-- Complex app -> React Query (TanStack Query)
  |   \-- Simpler needs -> SWR or custom hooks
  |
  |-- Authentication?
  |   |-- Token storage -> expo-secure-store
  |   \-- Token refresh -> Implement refresh flow
  |
  |-- Error handling?
  |   |-- Network errors -> Check connectivity first
  |   |-- HTTP errors -> Parse response, throw typed errors
  |   \-- Retries -> Exponential backoff
  |
  |-- Offline support?
  |   |-- Check status -> NetInfo
  |   \-- Queue requests -> React Query persistence
  |
  |-- Environment/API config?
  |   |-- Client-side URLs -> EXPO_PUBLIC_ prefix in .env
  |   |-- Server secrets -> Non-prefixed env vars (API routes only)
  |   \-- Multiple environments -> .env.development, .env.production
  |
  \-- Performance?
      |-- Caching -> React Query with staleTime
      |-- Deduplication -> React Query handles this
      \-- Cancellation -> AbortController or React Query

Common Mistakes

Wrong: No error handling

const data = await fetch(url).then((r) => r.json());

Right: Check response status

const response = await fetch(url);
if (!response.ok) throw new Error(`HTTP ${response.status}`);
const data = await response.json();

Wrong: Storing tokens in AsyncStorage

await AsyncStorage.setItem("token", token); // Not secure!

Right: Use SecureStore for sensitive data

await SecureStore.setItemAsync("token", token);

Example Invocations

User: "How do I make API calls in React Native?"

-> Use fetch, wrap with error handling

User: "Should I use React Query or SWR?"

-> React Query for complex apps, SWR for simpler needs

User: "My app needs to work offline"

-> Use NetInfo for status, React Query persistence for caching

User: "How do I handle authentication tokens?"

-> Store in expo-secure-store, implement refresh flow

User: "API calls are slow"

-> Check caching strategy, use React Query staleTime

User: "How do I configure different API URLs for dev and prod?"

-> Use EXPO_PUBLIC_ env vars with .env.development and .env.production files

User: "Where should I put my API key?"

-> Client-safe keys: EXPO_PUBLIC_ in .env. Secret keys: non-prefixed env vars in API routes only

User: "How do I load data for a page in Expo Router?"

-> See references/expo-router-loaders.md for route-level loaders (web, SDK 55+). For native, use React Query or fetch.

Submitting Feedback

If you encounter errors, misleading or outdated information in this skill, report it so Expo can improve:

npx --yes submit-expo-feedback@latest --category skills --subject "expo-data-fetching" "<actionable feedback>"

Only submit when you have something specific and actionable to report. Include as much relevant context as possible.

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How to use it

Copy the folder

Take expo/expo-data-fetching from the repository into ~/.claude/skills for personal use, or into .claude/skills inside a project.

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Install what it needs

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