Unlike many older public-domain tafsirs, Safwat al-Tafasir is still under copyright. Official PDFs are rarely free. However, check these trusted Islamic digital libraries:
Provides the reason for revelation (Asbab al-Nuzul) for various verses. Why Seek an English Translation?
Safwat al-Tafasir (The Elite of Interpretations), written by Shaykh Muhammad Ali al-Sabuni