Developer Discovers Six Bugs While Building Quantum Computing Tools for Quantinuum’s Guppy Stack

The author, Kristian Koci, describes his experience developing three practical developer tools for Quantinuum’s guppy/HUGR quantum computing stack. These tools – qshelf, Estimand, and qmatchpoint – were built with a focus on correctness and verification rather than as simple demonstrations. The development process revealed six significant bugs in the ecosystem: four in guppylang itself and two in Google’s Qualtran library. The bugs included issues with unitary calculations, type handling, and discrepancies in resource estimation formulas. For instance, qshelf uncovered problems with quantum algorithm implementations, while Estimand identified errors in the resource estimation models that required verification against the original research papers. The author emphasizes that treating correctness as a primary concern, rather than an afterthought, led to these discoveries. This approach involved verifying every claim through actual compilation and mathematical reference checks, not just relying on documentation. The tools themselves serve specific purposes: qshelf provides a verified registry of quantum algorithms, Estimand estimates physical resource requirements for quantum circuits, and qmatchpoint integrates quantum error correction decoding. The author notes that these findings highlight the importance of rigorous verification in quantum computing development, even in mature libraries. The work demonstrates how a disciplined approach to correctness can uncover real issues that might otherwise go unnoticed in the development process. The author has made the tools available in repositories for others to use and has documented the findings for transparency.