<p>EEG recordings are typically long and contain large amounts of data, making manual cleaning a time-consuming and error-prone task. Automated preprocessing pipelines can facilitate the efficient and objective extraction of artifacts, enabling standardized and reproducible analyses. However, automated preprocessing pipelines typically remove data considered artifacts and return a subset of irreversibly transformed signals. This approach obfuscates preprocessing decisions and often makes it impossible to recover the original data or modify the preprocessing steps. Further, it complicates collaboration among research teams working on a common dataset, as different analyses may require specific preprocessing steps. Given the large amount of resources devoted to collecting EEG, tools that can efficiently and transparently preprocess data are greatly needed. PyLossless addresses this need by creating a non-destructive, automated preprocessing pipeline that maintains the continuous EEG structure. It offers a user-friendly API, is well documented, tested through continuous integration, easily deployable, and integrates with the popular MNE-Python environment. The pipeline also provides a browser-based quality control review (QCR) dashboard that allows researchers to visualize and edit automated artifact flags for sensors, time periods, and independent components. The end product of PyLossless is a lossless annotated data state that can be shared and used with analysis-specific artifact rejection policies, allowing for an optimal balance between flexibility and standardization.</p>