Supplementary material for "No detection of DMS or DMDS in the atmosphere of K2-18 b. From a joint analysis of JWST NIRISS, NIRSpec, and MIRI observations" by Luque et al., submitted to A&A Letters (2025). This repository contains: Transmission spectra — Reduced transmission spectra for NIRISS/SOSS at R~100 with exoTEDRF; NIRSpec/G395H at R~200 with exoTEDRF, Eureka!, and SPARTA; and MIRI/LRS at R~100 with exoTEDRF, Eureka!, and SPARTA. Retrievals — Corner plots and retrieval results (posterior samples and best-fit models). Two analyses are carried out. First, retrievals on the original JExoRES spectra presented in Madhusudhan et al. 2023 and Madhusudhan et al. 2025 using the open-source code PLATON. Second, retrievals on the independent transmission spectra from this work (one from the full exoTEDRF reduction, another from SPARTA's NIRSpec and MIRI reduction together with the NIRISS exoTEDRF reduction) using the SCARLET code (e.g., Benneke & Seager 2012, Piaulet et al. 2023). For any additional data requests or questions, please contact: rluque@uchicago.edu