FinTech Code Review

When to use this skill

• •Before finalizing any pull request or code block related to transactions, ledgers, or balances.
• •When implementing Cloud Functions that handle money.
• •When writing Firestore transactions.
• •When reviewing Flutter code that displays sensitive financial data.

How to use it

1. •Review for Financial Correctness:
   • •Ensure all monetary values are handled as integers (e.g., cents/micros) to avoid floating-point errors.
   • •Verify that positive/negative signs are strictly enforced (e.g., debits are negative, credits are positive).
2. •Check for Idempotency:
   • •Verify that all transfer/transaction functions use an eventId or idempotencyKey to prevent double-spending.
   • •Ensure Firestore writes are idempotent.
3. •Analyze Concurrency & Safety:
   • •Confirm that all ledger updates happen within a Firestore Transaction.
   • •Check for race conditions where two processes might read old balances simultaneously.
4. •Security Audit:
   • •Ensure service accounts are used for backend operations.
   • •Verify that the client cannot spoof transaction results.