Expense Tracker
Personal finance app for tracking spending, budgets, and category insights in real time.
Engineering Telemetry & Metrics
Bottlenecks & Scale Constraints
Most budgeting apps bury the one thing that matters, where the money actually went, under cluttered dashboards and slow manual entry. Tracking spend across categories meant exporting CSVs and building spreadsheets by hand.
Target Architecture & Execution
Built a fast, secure single-page app with instant transaction entry, custom categories, and live charts. A JWT-secured Express API aggregates spend server-side, while Recharts renders monthly trends and category breakdowns that update the moment a transaction lands.
Key Architectural Pillars
Instant Transaction Entry
Custom Categories & Budgets
Live Spend Analytics (Recharts)
JWT-Secured REST API
Data Pipeline & Node Flow
React SPA talks to a JWT-secured Express API. Transactions persist in MongoDB; an aggregation pipeline groups spend by category and month, returning chart-ready series the client renders with Recharts.
Client (React)
Implementation Snippet
MongoDB aggregation that rolls every transaction up by category for a given month, returning a sorted, chart-ready series in a single round trip instead of pulling raw rows to the client.
export async function spendByCategory(userId: string, month: string) {
return Transaction.aggregate([
{ $match: { userId, month, type: 'expense' } },
{ $group: {
_id: '$category',
total: { $sum: '$amount' },
count: { $sum: 1 },
} },
{ $project: { category: '$_id', total: 1, count: 1, _id: 0 } },
{ $sort: { total: -1 } },
]);
}Dossier Specifications
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