# rust-fintech

> Use when building financial, trading, or payment systems in Rust. Covers money handling, financial calculations, rounding, decimal precision with rust_decimal and BigDecimal, currency newtypes, ledger, journal entry, reconciliation, idempotency, ACID transactions, regulatory compliance, immutable transaction records, audit trails, checked arithmetic, and double-entry patterns.

- Author: peixotorms
- Repository: peixotorms/odinlayer-skills
- Version: 20260202221752
- Stars: 0
- Forks: 0
- Last Updated: 2026-02-07
- Source: https://github.com/peixotorms/odinlayer-skills
- Web: https://mule.run/skillshub/@@peixotorms/odinlayer-skills~rust-fintech:20260202221752

---

---
name: rust-fintech
description: Use when building financial, trading, or payment systems in Rust. Covers money handling, financial calculations, rounding, decimal precision with rust_decimal and BigDecimal, currency newtypes, ledger, journal entry, reconciliation, idempotency, ACID transactions, regulatory compliance, immutable transaction records, audit trails, checked arithmetic, and double-entry patterns.
---

# FinTech Development

## Domain Constraints

| Domain Rule | Design Constraint | Rust Implication |
|-------------|-------------------|------------------|
| Audit trail | Immutable records | Arc<T>, no mutation |
| Precision | No floating point | rust_decimal |
| Consistency | Transaction boundaries | Clear ownership |
| Compliance | Complete logging | Structured tracing |
| Reproducibility | Deterministic execution | No race conditions |

## Critical Rules

- **Never use f64 for money** — floating point loses precision. Use `rust_decimal::Decimal`.
- **All transactions must be immutable and traceable** — regulatory compliance requires event sourcing.
- **Money can't disappear or appear** — double-entry accounting with validated totals.

## Key Crates

| Purpose | Crate |
|---------|-------|
| Decimal math | rust_decimal |
| Date/time | chrono, time |
| UUID | uuid |
| Serialization | serde |
| Validation | validator |

## Currency Type Pattern

```rust
use rust_decimal::Decimal;

#[derive(Clone, Debug, PartialEq)]
pub struct Amount {
    value: Decimal,
    currency: Currency,
}

impl Amount {
    pub fn new(value: Decimal, currency: Currency) -> Self {
        Self { value, currency }
    }

    pub fn add(&self, other: &Amount) -> Result<Amount, CurrencyMismatch> {
        if self.currency != other.currency {
            return Err(CurrencyMismatch);
        }
        Ok(Amount::new(self.value + other.value, self.currency))
    }
}
```

## Design Patterns

| Pattern | Purpose | Implementation |
|---------|---------|----------------|
| Currency newtype | Type safety | `struct Amount(Decimal);` |
| Transaction | Atomic operations | Event sourcing |
| Audit log | Traceability | Structured logging with trace IDs |
| Ledger | Double-entry | Debit/credit balance |

## Common Mistakes

| Mistake | Domain Violation | Fix |
|---------|-----------------|-----|
| Using f64 | Precision loss | rust_decimal |
| Mutable transaction | Audit trail broken | Immutable + events |
| String for amount | No validation | Validated newtype |
| Silent overflow | Money disappears | Checked arithmetic |