Dear Dr. Holding and co-authors,

My general comment to the manuscript is that in some places, the toolbox is kind of described as if the authors would like to sell something. Also, it sometimes feels as if reading a manual. I realize that the subject of the paper sometimes rather coerces to such writing, but possibly the authors can avoid it to some extent. Please go through the text and consider where such text can be improved.

L26 „the biogeochemical development“ I find this a strange combination. Any better wording?

L27-28 “to monitor the health of the oceans” I think speaking of health in this context is not scientifically objective, and not necessary here. Please use other wording.

L31 delete: and the toolbox is already being used by scientists across multiple disciplines (this is not info for a scientific paper)

L74 Shutler et al. (2016) and Woolf et al. (2016). (format)
L76 … by Woolf et al. (2016) and … (format)

L86-87 (e.g., Ho et al., 2006; Nightingale et al., 2000; Wanninkhof, 2014). (format)
L110-111 “and broadened the range of possible applications to which it can be applied.” Delete “to which it can be applied” because this does not add any info.

L165 Suggested: … with the reference data published in Holding et al. (2018).

§2.1 While I was reading this, it felt like reading a manual. Although this part of the manuscript contains important information, I think a large part should be transferred to the supplementary material or appendix, as this is not the kind of info for a scientific paper. Please consider how best to do this.

L273 Goddijn-Murphy (typo)
L354-356 “It is advisable to always use the most up-to-date version of FluxEngine which can be found via http://github.com/oceanfluxghg/FluxEngine.” This is not a sentence that belongs in a scientific paper.

L464-465 from 28 January 2015 to 9 September 2015 (format)
Fig.5 The units of xCO2 and fCO2 contain strange symbols, please correct.

L531 … of Nightingale et al. (2000) … (format)
L532 from Pereira et al. (2018). (format)

L622 Zappa et al. (2007) (typo)
L685 Datasets used: SOCAT is not listed here. Is there any reason for that?

L831 pages: 1937-1949

Thanks and best wishes
Mario Hoppema