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

Full cache header analysis

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 "" 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 "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:

Network tab → Select request → Headers section
Filter by: cache or x-drupal
Disable cache: Network tab → Check "Disable cache"
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

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

Compare Anonymous vs Authenticated Headers

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

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

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

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/

http-cache-tools

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Get headers only (-I = HEAD request, -s = silent)

GET request with headers shown (-i includes headers in output)

Follow redirects (-L)

Filter Drupal cache headers

Full cache header analysis

Just Drupal-specific headers

With session cookie (simulate logged-in user)

With basic auth

With bearer token

Force cache miss with Cache-Control header

Add random query string to bypass cache

Pragma no-cache (legacy)

Show timing breakdown

Simple total time

From SparkFabrik container

Inside container

Expected output for cached page:

X-Drupal-Cache: HIT

X-Drupal-Dynamic-Cache: HIT

Cache-Control: max-age=3600, public

Anonymous request

Authenticated request (with session cookie)

Expected:

Anonymous: X-Drupal-Cache: HIT, Cache-Control: public

Authenticated: X-Drupal-Dynamic-Cache: HIT, Cache-Control: private

Enable debug headers first (in settings.local.php):

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

Then check all cache metadata

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

Step 1: Check current cache status

X-Drupal-Cache: HIT

Step 2: Edit the node (via UI or drush)

Step 3: Verify cache miss after invalidation

X-Drupal-Cache: MISS

Step 4: Confirm next request is cached

X-Drupal-Cache: HIT

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

cache-debug.sh - Run from inside drupal-tools container

Usage from SparkFabrik project

Watch cache status every 2 seconds

Or with timestamp

List of URLs to check

Enter container as root

Install httpie

Headers only

With specific headers

Filter headers

Compare anonymous vs authenticated

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)

Extract session cookie

cache-compare.sh - Compare anonymous vs authenticated caching

Anonymous diagnosis

Authenticated diagnosis

Anonymous only

With authenticated comparison

SparkFabrik: Open interactive shell

SparkFabrik: One-off command

Generic Docker Compose

Source Transparency

Related Skills

drupal-lazy-builders

drupal-cache-debugging

drupal-cache-contexts