Plaid Expert

2. Transactions

Purpose: Access transaction history for budgeting, expense tracking, and financial insights.

Features:

• Up to 24 months of history
• Categorized transactions
• Merchant information
• Pending and posted transactions

3. Identity

Purpose: Verify user identity through bank account ownership.

Data retrieved:

• Account holder names
• Email addresses
• Phone numbers
• Physical addresses

4. Balance

Purpose: Real-time account balance checking to prevent payment failures.

Use cases:

• Insufficient funds detection
• Payment preflight checks
• Account monitoring

5. Investments

Purpose: Access holdings and transactions from investment accounts.

Coverage:

• Stocks, bonds, ETFs
• 401(k), IRA, brokerage accounts
• Real-time valuations

6. Liabilities

Purpose: Loan and credit data access.

Coverage:

• Student loans
• Mortgages
• Credit cards
• Auto loans

Plaid Link Integration

What is Link?

Plaid Link is the client-side component that users interact with to securely connect their bank accounts. It's a modal/iframe that handles the entire authentication flow.

Link Flow

1. User clicks "Connect Bank Account"
2. Link modal opens
3. User searches for their bank
4. User enters credentials (or OAuth)
5. User selects accounts to link
6. Link returns a public_token
7. Exchange public_token for access_token server-side

Frontend Integration (React)

Install:

npm install react-plaid-link

Implementation:

import { usePlaidLink } from 'react-plaid-link';

function PlaidLinkButton() {
  const [linkToken, setLinkToken] = useState(null);

  // 1. Create link token (call your backend)
  useEffect(() => {
    async function createLinkToken() {
      const response = await fetch('/api/plaid/create-link-token', {
        method: 'POST',
      });
      const data = await response.json();
      setLinkToken(data.link_token);
    }
    createLinkToken();
  }, []);

  // 2. Configure Link
  const { open, ready } = usePlaidLink({
    token: linkToken,
    onSuccess: async (public_token, metadata) => {
      // 3. Exchange public token for access token
      await fetch('/api/plaid/exchange-token', {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify({ public_token }),
      });
    },
    onExit: (err, metadata) => {
      if (err) console.error(err);
    },
  });

  return (
    <button onClick={() => open()} disabled={!ready}>
      Connect Bank Account
    </button>
  );
}

Backend: Create Link Token

Node.js example:

const plaid = require('plaid');

const client = new plaid.PlaidApi(
  new plaid.Configuration({
    basePath: plaid.PlaidEnvironments.sandbox,
    baseOptions: {
      headers: {
        'PLAID-CLIENT-ID': process.env.PLAID_CLIENT_ID,
        'PLAID-SECRET': process.env.PLAID_SECRET,
      },
    },
  })
);

// Create link token
app.post('/api/plaid/create-link-token', async (req, res) => {
  const request = {
    user: {
      client_user_id: req.user.id, // Your app's user ID
    },
    client_name: 'Your App Name',
    products: ['auth', 'transactions'],
    country_codes: ['US'],
    language: 'en',
  };

  try {
    const response = await client.linkTokenCreate(request);
    res.json({ link_token: response.data.link_token });
  } catch (error) {
    res.status(500).json({ error: error.message });
  }
});

Backend: Exchange Public Token

Store access token securely in your database:

app.post('/api/plaid/exchange-token', async (req, res) => {
  const { public_token } = req.body;

  try {
    const response = await client.itemPublicTokenExchange({
      public_token: public_token,
    });

    const access_token = response.data.access_token;
    const item_id = response.data.item_id;

    // Store access_token securely in your database
    await db.users.update(req.user.id, {
      plaid_access_token: access_token,
      plaid_item_id: item_id,
    });

    res.json({ success: true });
  } catch (error) {
    res.status(500).json({ error: error.message });
  }
});

Retrieving Data

Get Auth (Account/Routing Numbers)

async function getAuthData(access_token) {
  const response = await client.authGet({
    access_token: access_token,
  });

  const accounts = response.data.accounts;
  const numbers = response.data.numbers;

  // ACH numbers
  const ach = numbers.ach[0];
  console.log('Account:', ach.account);
  console.log('Routing:', ach.routing);

  return { accounts, numbers };
}

Get Transactions

async function getTransactions(access_token) {
  const request = {
    access_token: access_token,
    start_date: '2024-01-01',
    end_date: '2024-12-31',
  };

  const response = await client.transactionsGet(request);
  let transactions = response.data.transactions;

  // Handle pagination
  while (transactions.length < response.data.total_transactions) {
    const paginatedRequest = {
      ...request,
      offset: transactions.length,
    };
    const paginatedResponse = await client.transactionsGet(paginatedRequest);
    transactions = transactions.concat(paginatedResponse.data.transactions);
  }

  return transactions;
}

Transaction object structure:

{
  transaction_id: 'abc123',
  account_id: 'xyz789',
  amount: 12.34, // Positive = money out, Negative = money in
  date: '2024-11-16',
  name: 'Starbucks',
  merchant_name: 'Starbucks',
  category: ['Food and Drink', 'Restaurants', 'Coffee Shop'],
  pending: false,
  payment_channel: 'in store'
}

Get Balance

async function getBalance(access_token) {
  const response = await client.accountsBalanceGet({
    access_token: access_token,
  });

  const accounts = response.data.accounts;
  accounts.forEach(account => {
    console.log(`${account.name}: ${account.balances.current}`);
  });

  return accounts;
}

Get Identity

async function getIdentity(access_token) {
  const response = await client.identityGet({
    access_token: access_token,
  });

  const identity = response.data.accounts[0].owners[0];
  console.log('Name:', identity.names[0]);
  console.log('Email:', identity.emails[0].data);
  console.log('Phone:', identity.phone_numbers[0].data);

  return response.data;
}

Webhooks

Setup Webhook URL

Configure in Plaid Dashboard or via API when creating link token:

{
  webhook: 'https://your-domain.com/api/plaid/webhook',
}

Webhook Verification

Verify webhook authenticity:

const crypto = require('crypto');

app.post('/api/plaid/webhook', express.json(), async (req, res) => {
  const { webhook_type, webhook_code } = req.body;

  // Verify webhook signature
  const plaidSignature = req.headers['plaid-verification'];
  const timestamp = req.headers['plaid-timestamp'];

  const payload = JSON.stringify(req.body);
  const hash = crypto
    .createHmac('sha256', process.env.PLAID_WEBHOOK_SECRET)
    .update(`${timestamp}.${payload}`)
    .digest('hex');

  if (hash !== plaidSignature) {
    return res.status(401).send('Invalid signature');
  }

  // Handle webhook events
  if (webhook_type === 'TRANSACTIONS') {
    switch (webhook_code) {
      case 'INITIAL_UPDATE':
        console.log('Initial transactions available');
        break;
      case 'DEFAULT_UPDATE':
        console.log('New transactions available');
        // Fetch new transactions
        break;
      case 'TRANSACTIONS_REMOVED':
        console.log('Transactions removed');
        break;
    }
  }

  res.json({ received: true });
});

Common webhook events:

• TRANSACTIONS: INITIAL_UPDATE - First batch ready
• TRANSACTIONS: DEFAULT_UPDATE - New transactions available
• ITEM: ERROR - Connection issue
• ITEM: PENDING_EXPIRATION - Credentials expiring soon
• AUTH: AUTOMATICALLY_VERIFIED - Micro-deposit verification complete

Environments

Sandbox (testing):

basePath: plaid.PlaidEnvironments.sandbox

• Test credentials: user_good / pass_good
• No real bank connections
• Simulate transactions

Development (limited live connections):

basePath: plaid.PlaidEnvironments.development

• Up to 100 live bank connections
• Free for testing

Production (live):

basePath: plaid.PlaidEnvironments.production

• Real bank connections
• Requires approval and billing

Error Handling

Update Mode (Re-authentication)

When credentials expire or change:

const { open } = usePlaidLink({
  token: linkToken,
  onSuccess: async (public_token, metadata) => {
    // Item re-linked successfully
  },
});

// Create link token with update mode
const request = {
  access_token: existing_access_token,
  // ... other config
};

Common Errors

ITEM_LOGIN_REQUIRED:

• User needs to re-authenticate
• Solution: Trigger Link in update mode

RATE_LIMIT_EXCEEDED:

• Too many requests
• Solution: Implement exponential backoff

PRODUCT_NOT_READY:

• Data still syncing
• Solution: Wait for webhook or retry

Security Best Practices

1. Never expose secret keys client-side:

   • Use PLAID_CLIENT_ID and PLAID_SECRET server-side only
   • Link tokens are safe for client use

2. Encrypt access tokens:

   • Store access tokens encrypted in database
   • Never log access tokens

3. Verify webhook signatures:

   • Prevents forged webhooks
   • Use crypto verification

4. Use HTTPS:

   • Required for webhook endpoints
   • Required for production

5. Implement proper user consent:

   • Clear disclosure about data access
   • Follow Plaid's branding guidelines

Next.js API Route Example

Create link token:

// app/api/plaid/create-link-token/route.ts
import { NextResponse } from 'next/server';
import { Configuration, PlaidApi, PlaidEnvironments } from 'plaid';

const client = new PlaidApi(
  new Configuration({
    basePath: PlaidEnvironments.sandbox,
    baseOptions: {
      headers: {
        'PLAID-CLIENT-ID': process.env.PLAID_CLIENT_ID!,
        'PLAID-SECRET': process.env.PLAID_SECRET!,
      },
    },
  })
);

export async function POST(req: Request) {
  const session = await getSession();

  const response = await client.linkTokenCreate({
    user: { client_user_id: session.user.id },
    client_name: 'Your App',
    products: ['auth', 'transactions'],
    country_codes: ['US'],
    language: 'en',
  });

  return NextResponse.json({ link_token: response.data.link_token });
}

Testing in Sandbox

Test credentials:

• Username: user_good
• Password: pass_good
• MFA: 1234

Test institutions:

• "Platypus Bank" - Full feature support
• "Tartan Bank" - OAuth flow
• "Houndstooth Bank" - Error testing

Useful Resources

• Official Docs: https://plaid.com/docs/
• API Reference: https://plaid.com/docs/api/
• Plaid Link: https://plaid.com/docs/link/
• Webhooks: https://plaid.com/docs/api/webhooks/
• Quickstart: https://github.com/plaid/quickstart

Implementation Checklist

• Sign up for Plaid account
• Get client ID and secret keys
• Install Plaid SDK: npm install plaid react-plaid-link
• Set environment variables
• Implement link token creation endpoint
• Implement token exchange endpoint
• Integrate Plaid Link on frontend
• Store access tokens securely (encrypted)
• Set up webhook endpoint with verification
• Handle ITEM_LOGIN_REQUIRED errors
• Test with sandbox credentials
• Request production access
• Implement error handling and retry logic
• Add proper user consent/disclosure