According to the
Mairie de Paris, almost 90% of paid parking places will be free in August.
Which ones? Look at the
horodateur (the small kiosk where normally you would pay for your ticket), and it should specifically mention "
Gratuit les samedis, dimanches, jours fériés et mois d'août" (free Saturdays, Sundays, holidays, and the month of August). If in doubt, press the yellow button and the machine should display "
stationnement gratuit".
Spaces which remain paid are those rotating and visitor spaces where the
horodateur says "
Gratuit les dimanches et jours fériés" (free on Sundays and holidays).