AI-native full-stack developer. I build software end to end, from domain model and database to integrations, interface, tests, and deployment. I use AI coding tools as a force multiplier and keep correctness, security, and auditability in my own hands.

My focus is fintech and accounting automation: systems where a wrong number is worse than no number, so every figure must be traceable and every automated action reviewable.

Case studies with the story behind each project: aryanmadaan.myportfolio.com

Shimline: bookkeeping automation engine for QuickBooks Online

An evidence-native engine that pulls QuickBooks Online data over OAuth 2.0, rebuilds the ledger in double entry, and runs 16 deterministic accounting checks. Each defect becomes a correction proposal that a human approves; the engine then writes it back idempotently, verifies it by read-back, and reconciles.

• 848 tests: property-based tests, a grammar fuzzer, and a Beancount differential oracle
• Canadian GST/HST return preparation, bank statement matching, and job costing
• Multi-tenant firm workspace with TOTP MFA, separation of duties, and an append-only audit log
• Python · FastAPI · SQLite · HTMX · WeasyPrint

OweAhead: Making Tax Digital software for UK sole traders

Tax planning and digital recordkeeping for HMRC Making Tax Digital. A pure, deterministic, versioned tax engine (integer pennies, GOV.UK-sourced rates) estimates Income Tax and Class 4 NIC, with CSV bank import, user-authored bookkeeping rules, private receipts, quarterly reconciliation and close, and a simulated HMRC provider.

• 965 tests plus Playwright end-to-end journeys with accessibility checks
• PostgreSQL row-level security, fail-closed production configuration, and malware-scanned uploads
• Next.js 16 · React 19 · TypeScript · PostgreSQL · Drizzle · Tailwind

TaxDesk OS: practice management and ITR preparation for Indian CA offices

An operations command center for Indian tax practices (clients, cases, expiring client upload links, document custody, fees and PDFs) with a Tax Desk built on a deterministic, versioned AY 2026-27 income tax engine. Every rule cites committed statutory text, every figure traces back to a ledger row, and filing readiness is gated by validation, client approval and qualified-reviewer sign-off.

• 2,400+ automated checks: 1,861 unit tests, 312 hostile-client security checks, Playwright end-to-end suites
• Supabase row-level security with guarded SECURITY DEFINER RPCs, AES-256-GCM encrypted PAN, audited reveals
• Next.js 15 · React 19 · TypeScript · Supabase / PostgreSQL · Tailwind

Python FastAPI TypeScript Next.js React PostgreSQL Supabase SQL / SQLite OAuth 2.0 REST API integrations QuickBooks Online API HTMX HTML/CSS pytest property-based testing Linux / Nginx / systemd security hardening AI-assisted development

🌐 Portfolio: aryanmadaan.myportfolio.com
💼 LinkedIn: linkedin.com/in/aryanmadaan
📫 aryanmadaan@gmail.com