You need Go and Hugo installed.

hugo mod get -u 
hugo mod npm pack
npm install

hugo server -D --debug --baseURL="http://localhost:1313/docs/cloud/"

Theme version, defined in go.mod, should match a commit on Gatling theme git repository (main branch) :

require github.com/gatling/gatling.io-doc-theme v0.0.0-AAAMMJJHHmmSS-<first 12 chars of commit id>

If you continue to encouter errors, check your installed Hugo version and update it if possible.

Check official documentation for details.

In case of issue such as failed to extract shortcode: template for shortcode "img" not found, run hugo mod clean.