diff --git a/.github/workflows/audit.yml b/.github/workflows/audit.yml
index 693a10d..248a9ac 100644
--- a/.github/workflows/audit.yml
+++ b/.github/workflows/audit.yml
@@ -2,20 +2,76 @@ name: Audit
 
 on:
   push:
+    branches:
+      - master
+  pull_request:
 
 jobs:
   lighthouse:
     runs-on: ubuntu-latest
     steps:
-      - name: Checkount
+      - name: Setup Hugo
+        uses: peaceiris/actions-hugo@v2
+        with:
+          hugo-version: latest
+          extended: true
+
+      - name: Checkout (pull_request)
+        if: github.event.pull_request
         uses: actions/checkout@v2
         with:
           submodules: recursive
           fetch-depth: 0
-          ref: ${{github.event.pull_request.head.ref}}
-          repository: ${{github.event.pull_request.head.repo.full_name}}
+          ref: ${{ github.event.pull_request.base.ref }}
+
+      - name: Checkout (push)
+        if: github.event_name == 'push'
+        uses: actions/checkout@v2
+        with:
+          submodules: recursive
+          fetch-depth: 0
+          ref: ${{ github.event.before }}
+
+      - name: Build previous commit
+        run: |
+          hugo --printI18nWarnings --printPathWarnings --baseURL https://localhost -d old/
+
+      - name: Checkout current commit
+        uses: actions/checkout@v2
+        with:
+          submodules: recursive
+          fetch-depth: 0
+          clean: false
+
+      - name: Build current commit
+        run: |
+          hugo --printI18nWarnings --printPathWarnings --baseURL https://localhost
+          cp -r public/ new/
+          # copy, so that public/ stays, it will be needed for Caddy to serve
+
+      - name: Save full diff
+        run: diff -r old/ new/ | tee changes.diff || true
+
+      - name: Upload full diff
+        uses: actions/upload-artifact@v3
+        with:
+          name: diff
+          path: changes.diff
+
+      - name: Find changed URLs
+        id: changed_urls
+        env:
+          SCHEME: https
+          DOMAIN: localhost
+        run: |
+          urls="$(./changed-urls.sh)"
+          urls="${urls//'%'/'%25'}"
+          urls="${urls//$'\n'/'%0A'}"
+          urls="${urls//$'\r'/'%0D'}"
+          echo "::set-output name=urls::$urls"
 
       - name: Install Caddy
+        if: "${{ steps.changed_urls.outputs.urls != '' }}"
         run: |
           curl -1sLf 'https://dl.cloudsmith.io/public/caddy/stable/gpg.key' | sudo tee /etc/apt/trusted.gpg.d/caddy-stable.asc
           curl -1sLf 'https://dl.cloudsmith.io/public/caddy/stable/debian.deb.txt' | sudo tee /etc/apt/sources.list.d/caddy-stable.list
@@ -23,19 +79,12 @@ jobs:
           sudo apt install caddy
           sudo systemctl disable --now caddy
 
-      - name: Setup Hugo
-        uses: peaceiris/actions-hugo@v2
-        with:
-          hugo-version: latest
-          extended: true
-
-      - name: Build
-        run: hugo --printI18nWarnings --printPathWarnings --baseURL https://localhost
-
       - name: Compress
+        if: "${{ steps.changed_urls.outputs.urls != '' }}"
         run: time ./compress.sh
 
       - name: Audit using Lighthouse
+        if: "${{ steps.changed_urls.outputs.urls != '' }}"
         uses: treosh/lighthouse-ci-action@v9
         with:
           uploadArtifacts: true
@@ -44,6 +93,7 @@ jobs:
           serverBaseUrl: https://lhci.bbaovanc.com/
           # this should be safe since it only allows adding (not deleting) data
           serverToken: 926a24f2-90e4-48b1-809f-055b9408cf4b
+          urls: ${{ steps.changed_urls.outputs.urls }}
 
 
   audit:
diff --git a/changed-urls.sh b/changed-urls.sh
new file mode 100755
index 0000000..ef2324d
--- /dev/null
+++ b/changed-urls.sh
@@ -0,0 +1,8 @@
+#!/bin/sh
+
+diff -qrN old/ new/ |
+    grep -oP '(?<=\s)new\/\S*' |
+    xargs -d '\n' ls -1d 2>/dev/null |
+    grep 'index.html$' |
+    sed 's/index.html$//' |
+    sed "s/^new/${SCHEME:=http}:\/\/${DOMAIN:=example.com}/"
diff --git a/lighthouserc.yaml b/lighthouserc.yaml
index 57f735f..e06dc86 100644
--- a/lighthouserc.yaml
+++ b/lighthouserc.yaml
@@ -1,23 +1,5 @@
 ci:
   collect:
-    url:
-      - https://localhost/ # homepage
-      - https://localhost/links/ # very simple page
-
-      - https://localhost/blog/ # list page
-      - https://localhost/blog/the-redesign-of-my-website/ # average post, but no footnotes
-      - https://localhost/blog/blog-post-newsletter/ # average post, but WITH footnotes
-      - https://localhost/blog/caddy-is-the-best-webserver/ # another average post with footnotes, WITH code blocks
-      - https://localhost/blog/youtube-url-structures-you-should-know/ # youtube embed
-      - https://localhost/blog/copilot-post/ # lots of code blocks & text
-      - https://localhost/blog/github-copilot-experiments/ # heavy use of images
-
-      - https://localhost/categories/
-      - https://localhost/categories/linux/
-
-      - https://localhost/tags/
-      - https://localhost/tags/github-copilot/
-
     startServerCommand: sudo caddy run
     settings:
       chromeFlags: "--ignore-certificate-errors --throttling.cpuSlowdownMultiplier=2.4"