$ headless-seo-check http://127.0.0.1:4313 -a --verbose --no-color
--- stdout+stderr ---
headless-seo-check: checking http://127.0.0.1:4313 …
headless-seo-check: 4 URLs pointed at another host, checked on 127.0.0.1:4313 instead
headless-seo-check: 4 of 4 URLs selected, from http://127.0.0.1:4313/sitemap.xml
headless-seo-check http://127.0.0.1:4313
  4 of 4 URLs checked, from http://127.0.0.1:4313/sitemap.xml
  4 URLs pointed at another host, checked on 127.0.0.1:4313 instead

  ! http://127.0.0.1:4313/        rendering undetermined, 309 words, 2 links, 0 ms
      info  rendering mode undetermined — the response headers say nothing about caching [render-mode-unclear]
            checked twice, the second response said no more
      warn  no canonical link in the served HTML [canonical-missing]
  ! http://127.0.0.1:4313/static/ rendering undetermined, 309 words, 2 links, 0 ms
      info  rendering mode undetermined — the response headers say nothing about caching [render-mode-unclear]
            checked twice, the second response said no more
      warn  no canonical link in the served HTML [canonical-missing]
  x http://127.0.0.1:4313/shell/  rendering undetermined, 0 words, 0 links, 0 ms
      info  rendering mode undetermined — the response headers say nothing about caching [render-mode-unclear]
            checked twice, the second response said no more
      warn  no canonical link in the served HTML [canonical-missing]
      error the served HTML carries 0 words — Googlebot has to run JavaScript to see this page [empty-server-html]
            7 <script src> + 4 KB inline JS + an empty root container
      warn  no links to any other page on this host — the navigation is not in the served HTML [no-internal-links]
  x http://127.0.0.1:4313/gone/   HTTP 404
      error HTTP 404 — in your sitemap, but not on your site [sitemap-url-error]

  FAILED  2 blocking issues, 4 warnings
     1 × empty-server-html
     1 × sitemap-url-error

  What to do
    empty-server-html
      The server returns a shell — Googlebot has to execute JavaScript before it
      sees any content at all, and that rendering is queued, budgeted and never
      guaranteed. Move the content into the server render.
    sitemap-url-error
      This URL is in your sitemap but not on your site. Either restore the page or
      drop it from the sitemap — a sitemap full of errors reduces how much Google
      trusts the rest of it.

--- exit code: 1 ---