eric861129/plaid

Plaid Banking API Expert

Plaid connects applications to users' bank accounts for financial data access, payments, and identity verification.

When to Use

• Connecting bank accounts in fintech apps
• Implementing Plaid Link flow
• Retrieving transactions, balances, or account info
• Setting up ACH transfers
• Identity/income verification
• Handling Plaid webhooks

Core Products

| Product | Purpose | |---------|---------| | Auth | Bank account/routing numbers for ACH | | Transactions | Transaction history (up to 24 months) | | Identity | Verify user via bank account ownership | | Balance | Real-time account balances | | Investments | Holdings from investment accounts | | Liabilities | Loan and credit card data |

Quick Start

1. Install SDK

npm install plaid react-plaid-link

2. Create Plaid Client

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,
      },
    },
  })
);

3. Create Link Token (Server)

// POST /api/plaid/create-link-token
export async function POST(req: Request) {
  const response = await client.linkTokenCreate({
    user: { client_user_id: userId },
    client_name: "Your App",
    products: ["auth", "transactions"],
    country_codes: ["US"],
    language: "en",
  });

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

4. Plaid Link (Client)

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

function ConnectBank({ linkToken }) {
  const { open, ready } = usePlaidLink({
    token: linkToken,
    onSuccess: async (public_token, metadata) => {
      // Exchange for access_token on server
      await fetch("/api/plaid/exchange-token", {
        method: "POST",
        body: JSON.stringify({ public_token }),
      });
    },
  });

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

5. Exchange Token (Server)

// POST /api/plaid/exchange-token
export async function POST(req: Request) {
  const { public_token } = await req.json();

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

  // Store access_token securely (encrypted in database)
  await db.users.update(userId, {
    plaid_access_token: response.data.access_token,
    plaid_item_id: response.data.item_id,
  });

  return Response.json({ success: true });
}

Data Retrieval

Get Auth (Account/Routing Numbers)

const response = await client.authGet({ access_token });

const ach = response.data.numbers.ach[0];
console.log("Account:", ach.account);
console.log("Routing:", ach.routing);

Get Transactions

const response = await client.transactionsGet({
  access_token,
  start_date: "2024-01-01",
  end_date: "2024-12-31",
});

let transactions = response.data.transactions;

// Handle pagination
while (transactions.length < response.data.total_transactions) {
  const more = await client.transactionsGet({
    access_token,
    start_date: "2024-01-01",
    end_date: "2024-12-31",
    offset: transactions.length,
  });
  transactions = transactions.concat(more.data.transactions);
}

Transaction object:

{
  transaction_id: "abc123",
  amount: 12.34,           // Positive = outflow
  date: "2024-11-16",
  name: "Starbucks",
  merchant_name: "Starbucks",
  category: ["Food and Drink", "Coffee Shop"],
  pending: false,
}

Get Balance

const response = await client.accountsBalanceGet({ access_token });

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

Get Identity

const response = await client.identityGet({ access_token });

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

Webhooks

Setup Endpoint

// POST /api/plaid/webhook
export async function POST(req: Request) {
  const { webhook_type, webhook_code, item_id } = await req.json();

  switch (webhook_type) {
    case "TRANSACTIONS":
      if (webhook_code === "DEFAULT_UPDATE") {
        // New transactions available - fetch them
        await syncTransactions(item_id);
      }
      break;

    case "ITEM":
      if (webhook_code === "ERROR") {
        // Connection issue - prompt user to re-authenticate
        await notifyUserReauth(item_id);
      }
      break;
  }

  return Response.json({ received: true });
}

Key webhook events: | Event | Meaning | |-------|---------| | TRANSACTIONS: INITIAL_UPDATE | First batch ready | | TRANSACTIONS: DEFAULT_UPDATE | New transactions | | ITEM: ERROR | Connection issue | | ITEM: PENDING_EXPIRATION | Credentials expiring |

Environments

| Environment | Use Case | Base Path | |-------------|----------|-----------| | Sandbox | Testing | PlaidEnvironments.sandbox | | Development | Limited live (100 connections) | PlaidEnvironments.development | | Production | Live | PlaidEnvironments.production |

Sandbox Test Credentials

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

Error Handling

Re-authentication (Update Mode)

When credentials expire:

// Create link token for update mode
const response = await client.linkTokenCreate({
  user: { client_user_id: userId },
  client_name: "Your App",
  access_token: existingAccessToken, // Triggers update mode
  country_codes: ["US"],
  language: "en",
});

Common Errors

| Error | Solution | |-------|----------| | ITEM_LOGIN_REQUIRED | Re-authenticate via Link update mode | | RATE_LIMIT_EXCEEDED | Implement exponential backoff | | PRODUCT_NOT_READY | Wait for webhook or retry |

Security Best Practices

DO:

• Store access tokens encrypted in database
• Use environment variables for credentials
• Verify webhook signatures
• Use HTTPS for all endpoints

DON'T:

• Expose secret keys client-side
• Log access tokens
• Store credentials in code

Next.js App Router Example

// 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",
    webhook: `${process.env.NEXT_PUBLIC_URL}/api/plaid/webhook`,
  });

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

Implementation Checklist

• [ ] Sign up for Plaid account
• [ ] Get client ID and secret
• [ ] Install plaid and react-plaid-link
• [ ] Set environment variables
• [ ] Create link token endpoint
• [ ] Implement token exchange endpoint
• [ ] Integrate Plaid Link on frontend
• [ ] Store access tokens securely
• [ ] Set up webhook endpoint
• [ ] Handle re-authentication errors
• [ ] Test with sandbox credentials

Resources

• Docs: https://plaid.com/docs/
• API Reference: https://plaid.com/docs/api/
• Quickstart: https://github.com/plaid/quickstart