Duane M Moody
Failure was not an option where I learned to make decisions.
I build software the same way.
Principal-level engineering, system design, and technical leadership for teams that cannot afford fragile systems.
The work here is the thinking. The application of that thinking happens at XRiley.
Good systems are built on good decisions.
Papers for finished thinking. Notes for captured thinking.
Perspective
What I believe about building software
- Most engineering problems are not technical. They are decision problems.
- Architecture is not documentation. It is commitment.
- Simplicity is not the absence of complexity. It is the result of understanding.
- Systems fail where tradeoffs were avoided, not where constraints existed.
Experience
Selected Work
Selected Work reflects systems built under real constraints, where correctness, reliability, and clarity were not optional.
Loan Origination and Decision Systems
Designed and built loan origination systems in a regulated financial environment, including decision engines, loan processing workflows, and integrations with multiple third-party data providers. The work centered on defining clear system boundaries, ensuring deterministic behavior across workflows, and maintaining compliance as rules varied by jurisdiction. Systems remained coherent under growth, with decision logic able to evolve without destabilizing core workflows.
Geographic Compliance and Tax Systems
Built location-aware compliance and tax systems using spatial data, deriving correct regulatory behavior based on city, county, state, and regional boundaries. Implemented point-in-polygon logic to resolve applicable rules at runtime against geospatial boundary data. Accurate, location-aware systems capable of handling overlapping jurisdictions and complex regulatory requirements without manual intervention.
Decision Engines and State Machines
Developed decision engines and state machines for financial systems where outcomes depended on multi-factor inputs and regulatory constraints. Focused on making decision logic explicit, testable, and observable rather than embedded across distributed services. Reduced ambiguity in system behavior and improved the ability to reason about outcomes as conditions changed.
ACH Processing Systems
Designed and implemented ACH processing systems across RDFI and ODFI flows, with emphasis on data integrity, traceability, and operational clarity. Work included modeling transaction lifecycles, defining failure modes, and ensuring consistent behavior across distributed components. Delivered predictable processing pipelines with clear state transitions and reduced reconciliation complexity.
Personal Finance Aggregation and Enrichment
Built personal finance aggregation systems integrating multiple external data sources with inconsistent upstream behavior. Focused on normalization, categorization, and maintaining data consistency regardless of provider quality. Improved data reliability for downstream systems that depended on aggregated financial data being accurate and stable.
Featured writing
Papers
- Where Judgment Comes FromFeaturedEngineering judgment is not learned from frameworks or documentation. It is formed through experience where decisions carry real consequences.
- Building Systems That Cannot Be WrongLatest · NewIn regulated financial systems, correctness is not an optimization. It is the baseline. The architecture must reflect that.
Notes
- Determinism Is Not OptionalLatest · NewIf the same input does not produce the same result, the system cannot be trusted.
- Drift Is the Real Failure ModeNewSystems rarely fail because of a single mistake. They fail because small deviations are allowed to accumulate.
- Reconciliation Is Part of the SystemIf you cannot explain what happened, you do not control the system.
This site is the thinking. XRiley is where that thinking is applied.