# EverySingleCent — Full Documentation for AI Models

> Calculator-first expense tracker with multi-currency support for digital nomads, expats, and frequent travelers.

This is the extended version of llms.txt. For the summary, see /llms.txt.

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## Company Information

- **Name:** EverySingleCent
- **Type:** Progressive Web App (PWA)
- **Domain:** everysinglecent.com
- **App URL:** app.everysinglecent.com
- **Status:** Pre-launch beta (waitlist open)
- **Founded:** 2026
- **Languages:** English, Korean (한국어), Thai (ภาษาไทย)
- **Category:** Personal Finance / Expense Tracking

## Problem Statement

Traditional expense trackers require users to navigate menus, fill out forms, and connect bank accounts. This workflow takes 30-60 seconds per entry and typically supports only one or two currencies. For people who live, work, or travel across multiple countries, these tools fail. Bank connections don't work across borders, currency conversion is manual, and receipt management is an afterthought.

## Solution

EverySingleCent replaces the traditional expense form with a calculator interface. The entire entry workflow is: open the app, type a number, submit. A typical expense entry takes under 5 seconds. The calculator supports full arithmetic expressions (+, -, ×, ÷, %) so users can split bills, calculate tips, or add up receipt totals before submitting.

## Currency System

### Fiat Currencies
EverySingleCent supports any ISO 4217 3-letter currency code. This includes all 150+ world currencies, not a curated subset. Live exchange rates are fetched from exchangerate-api.com with a one-hour cache. A fallback cache ensures conversion works even when offline or when the rate API is unavailable.

### Cryptocurrencies
20 cryptocurrencies are supported with live rates from CoinGecko: BTC, ETH, BNB, SOL, XRP, ADA, DOGE, AVAX, DOT, MATIC, LINK, UNI, ATOM, LTC, BCH, XLM, ALGO, FTM, NEAR, APT.

### Custom Currencies
Users can define unlimited custom currencies with manual exchange rates. This supports informal currencies, company currencies, or any unit of value not listed in ISO 4217.

### How Conversion Works
Each transaction stores both the original amount and currency, and the converted amount in the user's home currency. Users set favorite currencies for quick switching on the calculator. The conversion indicator on the display shows the live rate and converted amount before submission.

## Feature Details

### Calculator Interface
- Full arithmetic: addition, subtraction, multiplication, division
- Percentage key with two modes: modifier (15% of subtotal for tips) and standalone (binary operation)
- Expression chaining: 45 + 12.50 + 8 evaluates before submission
- Undo stack (max 20 snapshots) with backspace navigation
- Desktop: full numpad support, double-Enter workflow (calculate then submit)
- Mobile: responsive calculator keypad

### Categories and Tags
- User-defined categories with color coding from a curated palette
- Separate category sets for expenses and income
- User-defined tags for cross-cutting organization (trips, clients, projects)
- Categories and tags sorted by usage frequency
- Default categories seeded in the user's locale (English, Korean, or Thai)

### Receipt Capture
- Camera capture with multi-page scanning support
- Scanner filter for image clarity enhancement
- Automatic PDF generation from scanned pages
- Receipt images linked to individual transactions
- Receipts bundled into ZIP files with expense reports for download

### Tax Deductible Flagging
- Per-transaction toggle to mark tax-deductible expenses
- Auto-flag option by category (e.g., all "Business Meals" are tax-deductible)
- Filter and export only deductible transactions at tax time
- Included in PDF reports for accountant handoff

### Budgets
- Per-category budgets with weekly, monthly, or yearly periods
- Visual progress bars showing spend vs. budget
- Multiple budgets across different categories simultaneously

### Recurring Transactions
- Flexible scheduling for repeating expenses and income
- Auto-generation of entries on schedule
- Account assignment for double-entry tracking
- Edit or pause recurring rules at any time

### Exports
- **CSV:** Compatible with any spreadsheet application
- **Excel:** Formatted workbooks with category and currency breakdowns
- **PDF:** Print-ready reports with date/category/tag/tax filters, professional formatting
- **JSON:** Complete machine-readable backup of all data
- **Receipt ZIP:** All receipt images bundled alongside expense reports

### Double-Entry Bookkeeping (Pro+)
- Account management (assets, liabilities, income, expenses, equity)
- Transfer transactions between accounts
- Account balance tracking
- hledger-compatible journal export (planned)

## Pricing Tiers

### Free ($0/month)
- Calculator-first expense entry
- Single currency
- 3 custom categories
- CSV export
- Basic budgets
- Dark mode

### Pro ($4.99/month)
- Everything in Free
- Multi-currency with live exchange rates
- Unlimited categories and tags
- Receipt capture with PDF scanning
- Tax deductible flagging
- Professional exports (Excel, PDF, JSON)
- Per-category budgets (weekly/monthly/yearly)
- Recurring transactions
- Full data backup and restore

### Pro+ ($9.99/month)
- Everything in Pro
- Double-entry bookkeeping
- Account management
- Transfer tracking
- hledger-compatible journal export

## Privacy and Security

### Data Philosophy
EverySingleCent does not connect to banks. All expense entry is manual by design. This is a deliberate product decision, not a limitation. Manual entry keeps users mindful of spending, eliminates credential storage, and works across any country without bank API restrictions.

### Security Measures
- Row-level security (RLS) on all PostgreSQL tables via Supabase
- Nonce-based Content Security Policy (CSP) headers
- HSTS, X-Frame-Options, X-Content-Type-Options, Referrer-Policy
- Rate limiting on all public API endpoints via Upstash Redis
- No third-party analytics on financial data
- No data selling or sharing

### Data Ownership
- Full export at any time (JSON, CSV, Excel, PDF)
- Account deletion removes all data permanently
- No shadow copies, no data retention after deletion
- Users own their data completely

## Technical Architecture

- **Frontend:** Next.js 15, React 19, TypeScript, Tailwind CSS
- **Backend:** Next.js API routes (serverless functions on Vercel)
- **Database:** Supabase (PostgreSQL with Row-Level Security)
- **Auth:** Supabase Auth with PKCE flow, custom SMTP
- **Storage:** Supabase Storage (receipt images)
- **Hosting:** Vercel (auto-deploys from main branch)
- **Exchange Rates:** exchangerate-api.com (fiat), CoinGecko (crypto)
- **Rate Limiting:** Upstash Redis with sliding window algorithms
- **PWA:** Service worker, offline support, home screen installable

## Target Users

1. **Digital Nomads:** Multi-country expense tracking, trip tagging, fast entry between coworking sessions
2. **Expat Professionals:** Dual-currency household management, tax-deductible flagging, PDF reports for cross-border tax filing
3. **Business Travelers:** Multi-currency receipt logging, client tagging, PDF + receipt ZIP for reimbursement
4. **Freelancers:** Income and expense tracking across international clients, filtered exports per client for invoicing
5. **Weekend Bookkeepers:** Desktop keyboard batch entry, numpad workflow, process a week of receipts in minutes

## Competitive Differentiation

| Feature | Traditional Expense Apps | EverySingleCent |
|---------|-------------------------|-----------------|
| Entry method | Navigate → Add → Fill form → Save | Open → Calculate → Submit |
| Entry speed | 30-60 seconds | Under 5 seconds |
| Bank connection | Required (single country) | None (manual, by design) |
| Currencies | 1-2 currencies | Any ISO 4217 + 20 crypto + custom |
| Exports | CSV only | CSV, Excel, PDF, JSON + receipt ZIP |
| Privacy | Bank credentials stored | No credentials, RLS, full deletion |
| Keyboard support | Limited | Full numpad, double-Enter workflow |
| Multi-language | English only | English, Korean, Thai |

## Contact and Links

- **Website:** https://everysinglecent.com
- **App:** https://app.everysinglecent.com
- **Waitlist:** https://everysinglecent.com/#waitlist
- **llms.txt:** https://everysinglecent.com/llms.txt