fintech-engineer

name	fintech-engineer
description	Fintech engineering expertise — payment processing (Stripe, Plaid), PCI DSS compliance, financial data modeling (double-entry bookkeeping), fraud detection patterns, bank-grade security (encryption, tokenization), open banking APIs, cryptocurrency/blockchain integration, regulatory compliance (KYC/AML), and idempotent financial transaction design. Use for payment systems, banking apps, trading platforms, and fintech infrastructure.
version	1.1.0
model	sonnet
invoked_by	both
user_invocable	true
tools	["Bash","Read","Write","Edit","WebFetch"]
best_practices	["All financial operations must be idempotent (use idempotency keys)","Use double-entry bookkeeping — never modify existing ledger entries","Never store raw card numbers — use tokenization (Stripe Elements, etc.)","Encrypt PII at rest (AES-256-GCM) and in transit (TLS 1.3)","All monetary values must be stored as integers (cents/smallest unit)","Every financial action requires an audit log entry"]
error_handling	graceful
streaming	not_applicable
verified	false
lastVerifiedAt	"2026-03-15T00:00:00.000Z"
source	builtin
trust_score	100
provenance_sha	67920cb5352819de

Fintech Engineer Skill

Overview

Financial technology engineering covering payment processing, ledger design, compliance, security, and fintech API integration. Core principle: correctness over speed — financial bugs have real monetary consequences.

Critical Rules

IRON LAWS OF FINANCIAL ENGINEERING:
1. Monetary values = integers (cents/pence/satoshis) — NEVER floats
2. All writes are idempotent (idempotency keys on every mutation)
3. Double-entry bookkeeping — debits always equal credits
4. Audit log every financial event — immutable, append-only
5. Fail safe — on error, roll back fully or do nothing
6. Never store card PANs — use tokenization providers
7. Assume network failures — design for exactly-once delivery

Monetary Value Handling

// ALWAYS store as integer (smallest currency unit)
// NEVER use floating point for money

// BAD — floating point arithmetic errors
const price = 9.99;
const tax = price * 0.08; // 0.7992000000000001 — WRONG

// GOOD — integer arithmetic in cents
const priceInCents = 999; // $9.99
const taxInCents = Math.round(priceInCents * 0.08); // 80 cents = $0.80

// Currency formatting (display only — never compute with these)
function formatMoney(cents: number, currency = 'USD'): string {
  return new Intl.NumberFormat('en-US', {
    style: 'currency',
    currency,
    minimumFractionDigits: 2,
  }).format(cents / );
}


  = {
  : ; 
  : ; 
};

 ():  {
   (a. !== b.)   ();
   { : a. + b., : a. };
}