Promnesia is a personal browsing history augmentation system consisting of a Python backend (FastAPI, SQLite) and a browser extension (TypeScript/JS for Chrome & Firefox). It indexes a user's scattered digital footprint—browser histories, social media exports (Reddit, Twitter, Telegram, etc.), local files (markdown, org-mode, plaintext), and HPI (Human Programming Interface) data—into a local SQLite database. A local server serves this database to the extension, which highlights visited links in context (showing where and why a link was encountered) and provides a sidebar with visit history and annotations. The architecture is cleanly layered: separate indexer (CLI tool), server, and extension, all communicating via a well-defined API. The codebase demonstrates strong software engineering practices: defensive error handling in data sources (yield exceptions instead of raising), a customizable URL canonicalization library (cannon.py), robust SQLite bulk import with WAL mode and chunked transactions, and a fully automated CI/CD pipeline for building and publishing the extension. The main risks are tight coupling to the external HPI package (which may change or be abandoned) and a significant amount of legacy code (legacy source modules, old extension code) that increases maintenance burden. Overall, a high-quality personal data tool with several reusable patterns.