Comparison of mean [Fe/H] derived from the literature (grey bars) and from [Fe/H] estimations presented in this paper (black bars). For each reference, the number of stars used to derive the mean is indicated. LMC metallicity from Romaniello et al. (2022) is presented taking account systematics. For details, see Sect. 4.3 for short-period Cepheids in the V band, Sect. 5.2 for long-period Cepheids in the V band, and Sect. 6.2 for the I-band relation. (a) LMC. (b) SMC.