Check Path is being treated like a URL not a file path

[erin-doyle]

With the following netlify.toml file:

[[plugins]]
package = "netlify-plugin-a11y"

  [plugins.inputs]
  checkPaths = [
    '/index.html',
  ]

I'm receiving the following error: Error: net::ERR_NAME_NOT_RESOLVED at http://build/index.html

My publish directory is set to build in the Build settings. I have no idea why the path is being prepended with http://. At first I thought maybe checkPaths must be expecting URL values but after experimenting with that it just appends whatever values I supply to http://build/. Is there something I'm doing wrong to trigger this behavior?