diff --git a/.github/workflows/ghcr.yml b/.github/workflows/ghcr.yml
index c7659113b..510b72d54 100644
--- a/.github/workflows/ghcr.yml
+++ b/.github/workflows/ghcr.yml
@@ -35,6 +35,9 @@ jobs:
           username: ${{ github.actor }}
           password: ${{ secrets.GITHUB_TOKEN }}
 
+      - name: Show Docker Context
+        run: ./test/check-docker-context.sh --report
+
       - name: Extract Docker metadata
         id: meta
         uses: docker/metadata-action@v5
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 30547f5a6..16a6bc121 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -56,6 +56,7 @@ jobs:
         fetch-depth: 0
         fetch-tags: true
         submodules: recursive
+    - run: ./test/check-docker-context.sh --report
     - run: ./test/test-images.sh
     - if: always()
       run: docker compose logs
diff --git a/test/check-docker-context.sh b/test/check-docker-context.sh
new file mode 100755
index 000000000..7e7076ca2
--- /dev/null
+++ b/test/check-docker-context.sh
@@ -0,0 +1,127 @@
+#!/bin/bash -eu
+set -o pipefail
+shopt -s inherit_errexit
+
+log() { echo "[$(basename "$0")] $*"; }
+
+# See: https://stackoverflow.com/questions/38946683/
+
+usage() {
+  cat <<EOF
+    USAGE
+      $0 --report
+      $0 [--min-size NUM --max-size NUM | --skip-size] [--min-count NUM --max-count NUM | --skip-count]
+EOF
+}
+
+if [[ $# = 0 ]]; then
+  usage
+  exit 1
+fi
+
+while [[ $# -gt 0 ]]; do
+  case "$1" in
+    --help) usage; exit;;
+
+    --report) skip_size=true; skip_count=true ;;
+
+    --min-size)   shift;min_size="$1" ;;
+    --max-size)   shift;max_size="$1" ;;
+    --skip-size)  skip_size=true ;;
+
+    --min-count)  shift;min_count="$1" ;;
+    --max-count)  shift;max_count="$1" ;;
+    --skip-count) skip_count=true ;;
+
+    *) log "!!! Unrecognised arg: $1"; exit 1 ;;
+  esac
+  shift
+done
+
+tmp="$(mktemp)"
+
+log "Creating custom docker build driver..."
+# Use custom builder to prevent log truncation:
+# > output clipped, log limit 200KiB/s reached
+docker buildx rm docker_context_checker || true
+docker buildx create --name docker_context_checker \
+    --driver-opt env.BUILDKIT_STEP_LOG_MAX_SIZE=-1 \
+    --driver-opt env.BUILDKIT_STEP_LOG_MAX_SPEED=-1
+docker buildx use docker_context_checker
+
+log "Building docker image..."
+(
+docker \
+    buildx build --load \
+    --no-cache --progress plain --file - . 2>&1 <<EOF
+FROM busybox
+COPY . /build-context
+WORKDIR /build-context
+RUN find . -type f
+RUN du -s .
+EOF
+) | tee "$tmp"
+
+vars="$(awk '
+  / DONE / { stage="" }
+
+  /RUN find \./ { stage="files" }
+  /RUN du -s .$/ { stage="size" }
+
+  stage == "files" { ++file_count }
+  stage == "size"  { total_size=$3 }
+
+  /exporting config/ { image_hash=$4 }
+
+  END {
+    print "file_count: " file_count "\n"
+    print "total_size: " total_size "\n"
+    print "image_hash: " image_hash "\n"
+  }
+' "$tmp")"
+
+
+file_count="$(echo "$vars" | grep file_count | cut -d: -f2)"
+total_size="$(echo "$vars" | grep total_size | cut -d: -f2)"
+docker_img="$(echo "$vars" | grep image_hash | cut -d: -f3)"
+
+cleanup() {
+  log "Removing docker image..."
+  docker image rm "$docker_img" >/dev/null
+}
+throw_err() {
+  log "!!!"
+  log "!!! $* !!!"
+  log "!!!"
+  cleanup
+  exit 1
+}
+
+log "File count: $file_count"
+if [[ "${skip_count-}" != "true" ]]; then
+  if [[ "$file_count" -lt "$min_count" ]] || [[ "$file_count" -gt "$max_count" ]]; then
+    throw_err "This is a surprising number of files - expected between $min_count and $max_count"
+  fi
+fi
+
+human_size() {
+  if [[ "$1" -gt 999999 ]]; then
+    echo "$(bc <<< "scale=3; $1 / 1000000") GB"
+  else
+    echo "$(bc <<< "scale=3; $1 / 1000") MB"
+  fi
+}
+
+log "Total size: $(human_size "$total_size")"
+if [[ "${skip_size-}" != "true" ]]; then
+  # N.B. busybox `du` outputs in kB
+  # See: https://www.busybox.net/downloads/BusyBox.html#du
+  if [[ "$total_size" -lt $min_size ]]; then
+    throw_err "This is a surprisingly small total size (expected min: $(human_size "$min_size"))"
+  elif [[ "$total_size" -gt $max_size ]]; then
+    throw_err "This is a surprisingly large total size (expected max: $(human_size "$max_size"))"
+  fi
+fi
+
+cleanup
+log "Everything looks OK."