HTTP Cache Debugging Tools

Practical tools and commands for inspecting HTTP cache headers and debugging Drupal caching behavior.

When to Use

• Inspecting cache response headers (X-Drupal-Cache, Cache-Control, etc.)
• Verifying cache hit/miss status
• Debugging why pages aren't caching
• Testing authenticated vs anonymous caching
• Analyzing Vary headers and cache variations

SparkFabrik Project Context

For container access and service URLs in SparkFabrik projects, see the pkg-skills reference.

Quick reminder:

• Inside container: http://drupal-nginx
• From host: Use fs-cli pkg:get-urls to get external URL

curl - The Essential Tool

Basic Header Inspection

# Get headers only (-I = HEAD request, -s = silent)
curl -sI https://example.com/

# GET request with headers shown (-i includes headers in output)
curl -si https://example.com/

# Follow redirects (-L)
curl -sIL https://example.com/

Cache-Specific Header Filters

# Filter Drupal cache headers
curl -sI https://example.com/ | grep -iE 'x-drupal|cache-control|age|vary|etag'

# Full cache header analysis
curl -sI https://example.com/ | grep -iE 'x-drupal|cache|age|vary|etag|expires|pragma|last-modified'

# Just Drupal-specific headers
curl -sI https://example.com/ | grep -i 'x-drupal'

Authenticated Requests

# With session cookie (simulate logged-in user)
curl -sI -H "Cookie: SESSabc123=xyz789" https://example.com/

# With basic auth
curl -sI -u username:password https://example.com/

# With bearer token
curl -sI -H "Authorization: Bearer TOKEN" https://example.com/

Cache Bypass Testing

# Force cache miss with Cache-Control header
curl -sI -H "Cache-Control: no-cache" https://example.com/

# Add random query string to bypass cache
curl -sI "https://example.com/?nocache=$(date +%s)"

# Pragma no-cache (legacy)
curl -sI -H "Pragma: no-cache" https://example.com/

Timing and Performance

# Show timing breakdown
curl -sI -w "\n\nTiming:\n  DNS: %{time_namelookup}s\n  Connect: %{time_connect}s\n  TLS: %{time_appconnect}s\n  TTFB: %{time_starttransfer}s\n  Total: %{time_total}s\n" https://example.com/

# Simple total time
curl -sI -w "\nTotal time: %{time_total}s\n" https://example.com/

Examples

Example 1: Quick Cache Status Check

Input: "Check if the homepage is being cached"

Output:

# From SparkFabrik container
make drupal-cli

# Inside container
curl -sI http://drupal-nginx/ | grep -iE 'x-drupal|cache-control'

# Expected output for cached page:
# X-Drupal-Cache: HIT
# X-Drupal-Dynamic-Cache: HIT
# Cache-Control: max-age=3600, public

Example 2: Compare Anonymous vs Authenticated

Input: "Check caching difference between anonymous and logged-in users"

Output:

# Anonymous request
echo "=== Anonymous ===" 
curl -sI http://drupal-nginx/node/1 | grep -iE 'x-drupal|cache-control|set-cookie'

# Authenticated request (with session cookie)
echo "=== Authenticated ==="
curl -sI -H "Cookie: SESSxyz=abc123" http://drupal-nginx/node/1 | grep -iE 'x-drupal|cache-control'

# Expected:
# Anonymous: X-Drupal-Cache: HIT, Cache-Control: public
# Authenticated: X-Drupal-Dynamic-Cache: HIT, Cache-Control: private

Example 3: Debug UNCACHEABLE Response

Input: "Find out why the page shows UNCACHEABLE"

Output:

# Enable debug headers first (in settings.local.php):
# $settings['http.response.debug_cacheability_headers'] = TRUE;

# Then check all cache metadata
curl -sI http://drupal-nginx/node/1 | grep -iE 'x-drupal'

# Look for:
# X-Drupal-Cache-Max-Age: 0  → Something set max-age to 0
# X-Drupal-Cache-Contexts: user  → High-cardinality context
# X-Drupal-Dynamic-Cache: UNCACHEABLE  → Page cannot be cached

Example 4: Test Cache Invalidation

Input: "Verify cache clears after content edit"

Output:

# Step 1: Check current cache status
curl -sI http://drupal-nginx/node/1 | grep 'X-Drupal-Cache'
# X-Drupal-Cache: HIT

# Step 2: Edit the node (via UI or drush)
drush php-eval "\Drupal::entityTypeManager()->getStorage('node')->load(1)->save();"

# Step 3: Verify cache miss after invalidation
curl -sI http://drupal-nginx/node/1 | grep 'X-Drupal-Cache'
# X-Drupal-Cache: MISS

# Step 4: Confirm next request is cached
curl -sI http://drupal-nginx/node/1 | grep 'X-Drupal-Cache'
# X-Drupal-Cache: HIT

Example 5: Check Vary Headers

Input: "See what the page varies on"

Output:

curl -sI http://drupal-nginx/ | grep -iE 'vary|x-drupal-cache-contexts'

# Example output:
# Vary: Cookie, Accept-Encoding
# X-Drupal-Cache-Contexts: languages:language_interface theme url.path user.permissions

# The Vary header tells proxies/CDNs what to cache separately
# Cache-Contexts show Drupal's internal cache variations

Example 6: Full Debug Script

Input: "Give me a complete cache debug for a URL"

Output:

#!/bin/bash
# cache-debug.sh - Run from inside drupal-tools container

URL="${1:-http://drupal-nginx/}"

echo "=== Cache Debug for: $URL ==="
echo ""

echo "--- Response Headers ---"
curl -sI "$URL" | grep -iE 'http/|x-drupal|cache|vary|age|etag|expires'

echo ""
echo "--- Timing ---"
curl -sI -w "DNS: %{time_namelookup}s | Connect: %{time_connect}s | TTFB: %{time_starttransfer}s | Total: %{time_total}s\n" -o /dev/null "$URL"

echo ""
echo "--- Cache Status Summary ---"
CACHE=$(curl -sI "$URL" | grep -i 'X-Drupal-Cache:' | cut -d' ' -f2 | tr -d '\r')
DYNAMIC=$(curl -sI "$URL" | grep -i 'X-Drupal-Dynamic-Cache:' | cut -d' ' -f2 | tr -d '\r')

echo "Page Cache: ${CACHE:-N/A}"
echo "Dynamic Cache: ${DYNAMIC:-N/A}"

if [ "$DYNAMIC" = "UNCACHEABLE" ]; then
  echo "⚠️  WARNING: Page is UNCACHEABLE - check for max-age:0"
fi

# Usage from SparkFabrik project
docker compose run --rm -it drupal-tools bash -c 'URL="http://drupal-nginx/node/1"; curl -sI "$URL" | grep -iE "x-drupal|cache"'

Example 7: Watch Cache Headers in Real-Time

Input: "Monitor cache status during development"

Output:

# Watch cache status every 2 seconds
watch -n 2 'curl -sI http://drupal-nginx/ | grep -iE "x-drupal|cache-control"'

# Or with timestamp
while true; do
  echo "=== $(date) ==="
  curl -sI http://drupal-nginx/ | grep -iE 'x-drupal'
  sleep 5
done

Example 8: Test Multiple URLs

Input: "Check cache status for multiple pages"

Output:

# List of URLs to check
URLS=(
  "http://drupal-nginx/"
  "http://drupal-nginx/node/1"
  "http://drupal-nginx/admin"
  "http://drupal-nginx/user/login"
)

for url in "${URLS[@]}"; do
  echo "=== $url ==="
  curl -sI "$url" | grep -iE 'x-drupal-cache|x-drupal-dynamic' || echo "No cache headers"
  echo ""
done

Alternative to curl: httpie

httpie provides more readable syntax with colorized output.

Installation

If not present in the drupal-tools container:

# Enter container as root
make drupal-cli-root

# Install httpie
apk add --no-cache httpie

Usage

# Headers only
http HEAD http://drupal-nginx/

# With specific headers
http http://drupal-nginx/ 'Cookie:SESSxyz=abc'

# Filter headers
http --print=h http://drupal-nginx/ | grep -i cache

# Compare anonymous vs authenticated
http --print=h HEAD http://drupal-nginx/node/1
http --print=h HEAD http://drupal-nginx/node/1 'Cookie:SESSxyz=abc'

Browser DevTools

For visual debugging:

1. Network tab → Select request → Headers section
2. Filter by: cache or x-drupal
3. Disable cache: Network tab → Check "Disable cache"
4. Preserve log: Keep requests across navigation

DevTools Cache Headers to Check

Header	Location	Meaning
X-Drupal-Cache	Response	Page Cache status
X-Drupal-Dynamic-Cache	Response	Dynamic Cache status
Cache-Control	Response	Browser/proxy caching rules
Age	Response	Seconds since cached by proxy
Vary	Response	What causes cache variations

Quick Reference

Task	Command
Check cache status	curl -sI URL | grep -i x-drupal
Full headers	curl -sI URL
Authenticated	curl -sI -H "Cookie: SESS=x" URL
Bypass cache	curl -sI -H "Cache-Control: no-cache" URL
Timing	curl -sI -w "TTFB: %{time_starttransfer}s\n" URL
Follow redirects	curl -sIL URL

Anonymous vs Authenticated Cache Analysis

This section helps analyze how Drupal caches pages for anonymous and authenticated users.

Step-by-Step Analysis

1. Get a Valid Session Cookie

First, log in to Drupal and extract the session cookie:

# Option A: From browser DevTools
# 1. Log in to Drupal
# 2. Open DevTools → Application → Cookies
# 3. Copy the SESS* cookie value (e.g., SESSabc123=xyz789)

# Option B: Via curl (if you have credentials)
curl -c cookies.txt -X POST \
  -d "name=admin&pass=password&form_id=user_login_form&op=Log+in" \
  http://drupal-nginx/user/login

# Extract session cookie
cat cookies.txt | grep SESS

2. Compare Anonymous vs Authenticated Headers

URL="http://drupal-nginx/node/1"

echo "========== ANONYMOUS REQUEST =========="
curl -sI "$URL" | grep -iE 'http/|x-drupal|cache-control|set-cookie|vary'

echo ""
echo "========== AUTHENTICATED REQUEST =========="
curl -sI -H "Cookie: SESSxxxxxxx=yyyyyyyy" "$URL" | grep -iE 'http/|x-drupal|cache-control|vary'

3. Interpret the Results

Key headers to analyze:

Header	Anonymous (expected)	Authenticated (expected)	Meaning
X-Drupal-Cache	HIT or MISS	Not present	Page Cache (only for anonymous)
X-Drupal-Dynamic-Cache	HIT	HIT or UNCACHEABLE	Dynamic Page Cache
Cache-Control	max-age=X, public	max-age=0, private, no-cache	Browser/proxy caching
Vary	Cookie, Accept-Encoding	Cookie, Accept-Encoding	Cache variations
Set-Cookie	May set session	Should not set new session	Session handling

Understanding Cache Behavior

Scenario 1: Optimal Caching (Anonymous)

X-Drupal-Cache: HIT
X-Drupal-Dynamic-Cache: HIT
Cache-Control: max-age=3600, public

✅ Good: Page is fully cached, served from Page Cache.

Scenario 2: Dynamic Cache Only (Anonymous)

X-Drupal-Cache: MISS
X-Drupal-Dynamic-Cache: HIT
Cache-Control: max-age=3600, public

⚠️ Partial: Page uses Dynamic Cache but not Page Cache. Check if there are session cookies being set.

Scenario 3: Uncacheable (Anonymous)

X-Drupal-Cache: MISS
X-Drupal-Dynamic-Cache: UNCACHEABLE
Cache-Control: must-revalidate, no-cache, private

❌ Problem: Page cannot be cached. Check for:

• max-age: 0 on render elements
• High-cardinality cache contexts (e.g., user)
• Session being started unexpectedly

Scenario 4: Authenticated User (Expected)

X-Drupal-Dynamic-Cache: HIT
Cache-Control: max-age=0, private, no-cache

✅ Expected: Authenticated pages should be private, Dynamic Cache can still help.

Scenario 5: Authenticated User Uncacheable

X-Drupal-Dynamic-Cache: UNCACHEABLE
Cache-Control: must-revalidate, no-cache, private

⚠️ Check: Even for authenticated users, Dynamic Cache should work. Look for max-age: 0 issues.

Full Comparison Script

#!/bin/bash
# cache-compare.sh - Compare anonymous vs authenticated caching

URL="${1:-http://drupal-nginx/}"
SESSION_COOKIE="${2:-}"

echo "╔════════════════════════════════════════════════════════════════╗"
echo "║  Cache Analysis: $URL"
echo "╚════════════════════════════════════════════════════════════════╝"
echo ""

echo "┌─────────────────────────────────────────────────────────────────┐"
echo "│ ANONYMOUS REQUEST                                               │"
echo "└─────────────────────────────────────────────────────────────────┘"
ANON_HEADERS=$(curl -sI "$URL")
echo "$ANON_HEADERS" | grep -iE 'http/|x-drupal|cache-control|vary|set-cookie'

ANON_PAGE_CACHE=$(echo "$ANON_HEADERS" | grep -i 'X-Drupal-Cache:' | awk '{print $2}' | tr -d '\r')
ANON_DYN_CACHE=$(echo "$ANON_HEADERS" | grep -i 'X-Drupal-Dynamic-Cache:' | awk '{print $2}' | tr -d '\r')
ANON_CACHE_CTRL=$(echo "$ANON_HEADERS" | grep -i 'Cache-Control:' | cut -d':' -f2 | tr -d '\r')

echo ""
echo "Summary:"
echo "  Page Cache:    ${ANON_PAGE_CACHE:-N/A}"
echo "  Dynamic Cache: ${ANON_DYN_CACHE:-N/A}"
echo "  Cache-Control: ${ANON_CACHE_CTRL:-N/A}"

if [ -n "$SESSION_COOKIE" ]; then
  echo ""
  echo "┌─────────────────────────────────────────────────────────────────┐"
  echo "│ AUTHENTICATED REQUEST                                          │"
  echo "└─────────────────────────────────────────────────────────────────┘"
  AUTH_HEADERS=$(curl -sI -H "Cookie: $SESSION_COOKIE" "$URL")
  echo "$AUTH_HEADERS" | grep -iE 'http/|x-drupal|cache-control|vary'

  AUTH_DYN_CACHE=$(echo "$AUTH_HEADERS" | grep -i 'X-Drupal-Dynamic-Cache:' | awk '{print $2}' | tr -d '\r')
  AUTH_CACHE_CTRL=$(echo "$AUTH_HEADERS" | grep -i 'Cache-Control:' | cut -d':' -f2 | tr -d '\r')

  echo ""
  echo "Summary:"
  echo "  Dynamic Cache: ${AUTH_DYN_CACHE:-N/A}"
  echo "  Cache-Control: ${AUTH_CACHE_CTRL:-N/A}"
fi

echo ""
echo "┌─────────────────────────────────────────────────────────────────┐"
echo "│ DIAGNOSIS                                                       │"
echo "└─────────────────────────────────────────────────────────────────┘"

# Anonymous diagnosis
if [ "$ANON_PAGE_CACHE" = "HIT" ]; then
  echo "✅ Anonymous: Page Cache is working"
elif [ "$ANON_DYN_CACHE" = "HIT" ]; then
  echo "⚠️  Anonymous: Only Dynamic Cache working (Page Cache MISS)"
elif [ "$ANON_DYN_CACHE" = "UNCACHEABLE" ]; then
  echo "❌ Anonymous: Page is UNCACHEABLE - needs investigation"
else
  echo "⚠️  Anonymous: Cache status unclear"
fi

# Authenticated diagnosis
if [ -n "$SESSION_COOKIE" ]; then
  if [ "$AUTH_DYN_CACHE" = "HIT" ]; then
    echo "✅ Authenticated: Dynamic Cache is working"
  elif [ "$AUTH_DYN_CACHE" = "UNCACHEABLE" ]; then
    echo "⚠️  Authenticated: Dynamic Cache not working"
  fi
  
  if echo "$AUTH_CACHE_CTRL" | grep -q "private"; then
    echo "✅ Authenticated: Correctly marked as private"
  else
    echo "❌ Authenticated: Should be private but isn't!"
  fi
fi

Usage:

# Anonymous only
./cache-compare.sh http://drupal-nginx/node/1

# With authenticated comparison
./cache-compare.sh http://drupal-nginx/node/1 "SESSabc123=xyz789"

Common Issues and Solutions

Symptom	Likely Cause	Solution
Anonymous gets UNCACHEABLE	Something sets max-age: 0	Enable debug headers, check for bad cache metadata
Anonymous gets Set-Cookie	Session started for anonymous	Check for code that calls \Drupal::currentUser() early
Anonymous Cache-Control: private	Session or user context	Look for user cache context being added
Page Cache always MISS	Vary on Cookie + session exists	Ensure anonymous users don't get sessions
Authenticated UNCACHEABLE	max-age: 0 in render array	Find element setting zero max-age

Debug Headers

Enable detailed cache debug headers in settings.local.php:

$settings['http.response.debug_cacheability_headers'] = TRUE;

This exposes additional headers:

• X-Drupal-Cache-Tags - Cache tags for invalidation
• X-Drupal-Cache-Contexts - What the page varies on
• X-Drupal-Cache-Max-Age - Minimum max-age from all elements

Container Quick Commands

# SparkFabrik: Open interactive shell
make drupal-cli

# SparkFabrik: One-off command
docker compose run --rm -it drupal-tools curl -sI http://drupal-nginx/

# Generic Docker Compose
docker compose exec php curl -sI http://localhost/