Direct File is a full-stack, multi-service tax preparation and electronic filing system built by the IRS for federal and state tax returns. The architecture is a microservices monorepo with a Spring Boot Java backend (REST APIs, PDF generation, S3/SQS/SNS/KMS integration), a Scala.js fact-graph engine (declarative tax computation rules shared between JVM and JavaScript), a React/TypeScript frontend (Vite, USWDS, Redux, i18n), and supporting services for submission batching, status tracking, email notifications, and state tax authority integration. The fact-graph is the core innovation: a domain-specific declarative rule system using typed nodes (Dollar, Tin, Enum) and composable operators (Sum, Maximum, Switch, Placeholder) to encode the Internal Revenue Code as a knowledge graph that can be evaluated both server-side and client-side. The frontend uses a declarative flow configuration (JSX trees of Screen, Gate, CollectionLoop) driven by fact-graph state. The system integrates with MeF (Modernized e-File) for submission, SADI for identity verification, and a State API for exporting federal data to third-party state filing tools. The repository is archived and no longer maintained, so it represents a frozen snapshot of the 2024 tax season codebase with known deprecations and hardcoded constants.