Building a Personal Finance App: Essential APIs and Architecture Guide

Building a personal finance app like Mint, YNAB, or Copilot requires integrating multiple APIs and services. This guide covers everything from bank connectivity to transaction enrichment, helping you build a competitive PFM app faster.

The PFM Tech Stack

A modern personal finance app typically needs these components:

• Bank Connectivity: Connect to users' bank accounts to fetch transactions
• Transaction Enrichment: Clean up and categorize raw transaction data
• Budgeting Engine: Track spending against user-defined budgets
• Analytics & Insights: Generate spending reports and trends
• Notifications: Alert users about bills, unusual spending, etc.

Step 1: Bank Account Connectivity

To access user transactions, you need to connect to their bank accounts. The main options are:

Plaid (US Market Leader)

Plaid connects to 12,000+ financial institutions in the US. They handle OAuth flows, credential storage, and transaction syncing.

• Coverage: US, Canada, UK, EU
• Pricing: ~$0.30-0.50 per connected account/month
• Best for: US-focused apps

TrueLayer (Europe)

TrueLayer is the leading Open Banking provider in Europe, with strong coverage across UK and EU banks.

• Coverage: UK, EU (PSD2 compliant)
• Pricing: Pay per API call
• Best for: European fintech apps

Belvo (Latin America)

Belvo specializes in Latin American banks, covering Mexico, Brazil, and Colombia.

Step 2: Transaction Enrichment

Raw bank transactions look like this:

{
  "date": "2025-02-15",
  "description": "POS DEBIT AMZN MKTP US*2K1AB0C9Z",
  "amount": -67.43
}

After enrichment with Easy Enrichment:

{
  "date": "2025-02-15",
  "description": "POS DEBIT AMZN MKTP US*2K1AB0C9Z",
  "amount": -67.43,
  "merchant_name": "Amazon",
  "category": "Shopping",
  "subcategory": "Online Marketplace",
  "logo_url": "https://logo.clearbit.com/amazon.com",
  "mcc_code": "5942",
  "is_subscription": false
}

The difference is massive. Enriched transactions enable:

• Visual transaction lists: Show merchant logos instead of cryptic codes
• Automatic categorization: No manual tagging needed
• Subscription tracking: Identify recurring charges
• Spending insights: "You spent $340 on restaurants this month"

Easy Enrichment: Best for PFM Apps

Easy Enrichment is purpose-built for personal finance apps. One API call returns:

• Clean merchant name
• Category & subcategory
• Merchant logo URL
• MCC code
• Subscription detection
• CO₂ footprint estimate

// Enrich transactions from Plaid
async function enrichPlaidTransactions(plaidTxns) {
  const response = await fetch('https://api.easyenrichment.com/enrich/batch', {
    method: 'POST',
    headers: {
      'Authorization': 'Bearer YOUR_API_KEY',
      'Content-Type': 'application/json'
    },
    body: JSON.stringify({
      transactions: plaidTxns.map(t => ({
        description: t.name,
        amount: t.amount,
        mcc: t.merchant_data?.mcc // Pass MCC if available
      }))
    })
  });

  return response.json();
}

Step 3: Building Core Features

Budgeting

With categorized transactions, budgeting becomes straightforward:

// Calculate category spending
function getCategorySpending(transactions, category) {
  return transactions
    .filter(t => t.category === category)
    .reduce((sum, t) => sum + Math.abs(t.amount), 0);
}

// Check budget status
function getBudgetStatus(transactions, budgets) {
  return budgets.map(budget => ({
    category: budget.category,
    limit: budget.amount,
    spent: getCategorySpending(transactions, budget.category),
    remaining: budget.amount - getCategorySpending(transactions, budget.category)
  }));
}

Subscription Tracking

Easy Enrichment flags subscriptions automatically:

// Get all subscriptions
const subscriptions = enrichedTransactions
  .filter(t => t.is_subscription)
  .reduce((acc, t) => {
    const existing = acc.find(s => s.merchant === t.merchant_name);
    if (existing) {
      existing.occurrences++;
    } else {
      acc.push({
        merchant: t.merchant_name,
        logo: t.logo_url,
        amount: t.amount,
        occurrences: 1
      });
    }
    return acc;
  }, []);

// Monthly subscription cost
const monthlySubCost = subscriptions.reduce((sum, s) => sum + Math.abs(s.amount), 0);

Architecture Recommendations

• Cache enrichment results: Store enriched data in your database. Don't re-enrich the same transaction.
• Async processing: Enrich transactions in background jobs, not on user request.
• Webhook-driven syncing: Use Plaid webhooks to sync new transactions automatically.
• Separate read/write databases: Use read replicas for analytics queries.

Cost Optimization

For a PFM app with 10,000 users averaging 200 transactions/month:

*With caching, you'll only enrich unique transactions, reducing costs by 60-80%.