Context. The flat-spectrum radio quasar (FSRQ) OP 313 entered an enhanced activity phase in November 2023 and has undergone multiple flares since then. This activity has motivated the organization of several large multi-wavelength campaigns, including two deep observations from the hard X-ray telescope NuSTAR. We investigate the broadband emission from OP 313 during these two observations, based on a new unified analysis framework, with data in the optical to γ rays. Aims. Traditional methods for analyzing blazar emission often rely on proprietary software tailored to specific instruments, making it challenging to integrate and interpret data from multiwavelength campaigns in a comprehensive way. This study demonstrates the feasibility of utilizing gammapy, an open-source Python package, together with common data formats originally developed for γ-ray instrumentation to perform a consistent multi-instrument analysis. This enables a forward-folding approach that fully incorporates source observations, detector responses, and various instrumental and astrophysical backgrounds. This methodology has been applied to an example set of recent data collected from the distant quasar OP 313. Methods. We present a comprehensive data reconstruction and analysis for instruments including the Liverpool Telescope's IO:O detector, Swift-UVOT, Swift-XRT, NuSTAR, and Fermi-LAT. The resulting spectral analysis has been validated against the native tools for each instrument. Additionally, we developed a multiwavelength phenomenological model of the source emission, encompassing the optical to γ-ray bands and incorporating absorption components across different energy regimes. Results. We have introduced and validated a new unified framework for multiwavelength forward-folding data analysis based on gammapy and open data formats, demonstrating its application to spectral data from the quasar OP 313. This approach provides a more statistically correct treatment of the data than fitting a collection of flux points extracted from the different instruments. This study is the first to use a common event data format and analysis tool covering 11 orders of magnitude in energy, from approximately 1 eV to 100 GeV. The high-level event data, instrument response functions, and models are provided in a gammapy-compatible format, ensuring accessibility and reproducibility of scientific results. A brief discussion on the origin of the broadband emission of OP 313 is also included in this work.