David,

> +        (base32
> +         "1d9pxcgmln4gls99vwj1h24qv0lz7fb2jqmqrsiv1pid1snc125x"))))
[…]
> +    (home-page
> +     "https://github.com/marshmallow-code/marshmallow-jsonapi")
> +    (synopsis
> +     "JSON API 1.0 (https://jsonapi.org) formatting with 
> marshmallow")

Nitpick: none of these need to be on separate lines (after 
removing the URL from the description).

Guix synopses and descriptions support (a comfortable subset of) 
Texinfo.  You can include hyperlinks in Texinfo with

  @uref{https://your.url/here, optional description}

For subjective reasons I decided to keep only the URL in the 
description.

> +    (description
> +     "JSON API 1.0 (https://jsonapi.org) formatting with 
> marshmallow")

Descriptions should consist of full sentences.  A single line is 
way too short.  Upstream has a fine description that fits our 
standards, so I adapted it:

+    (description
+     "The marshmallow-jsonapi package provides a simple way to 
produce
+@uref{https://jsonapi.org, JSON:API}-compliant data in any Python 
Web framework.
+It includes optional utilities to integrate with Flask.")

> +    (license license:expat))) ; MIT license

No need for this comment.

Thanks!

T G-R