The Cache Audit: A Step-by-Step Technical Review to Unlock Traffic and Performance

Hook: Your pages load fast, but are your caches leaving traffic on the table?

Slow page loads, runaway bandwidth bills, and opaque cache behavior are core pain points for engineering teams in 2026. You can have a fast origin and a modern CDN, yet still miss conversions because cache rules, headers, and invalidation workflows are misaligned. Treat caching like SEO: run a repeatable, prioritized audit that surfaces high-impact fixes. This article gives a technical, checklist-driven cache audit you can run in a day and operationalize across teams.

The inverted pyramid: What matters first in a cache audit

Start with what impacts users and cost the most, then widen the scope. The top priorities are:

• Cache hit rate — the single metric that maps directly to latency and bandwidth savings.
• Cacheability of revenue-generating pages and critical assets.
• TTL strategy and header hygiene for consistent behavior across CDN, edge, and origin.
• Invalidation and purge workflows within CI/CD and editorial processes.
• Monitoring and observability so you catch regressions early.

Why run a cache audit in 2026?

Late 2025 and early 2026 saw broader adoption of edge compute, HTTP/3 adoption surpassing 60% on many properties, and CDNs adding ML-driven caching heuristics. That makes caching both more powerful and more complex. The audit aligns cache policy with modern stack dynamics and ensures cache behavior supports traffic growth and conversion goals.

Quick prerequisites — tools and data to gather

Before you start, collect these data sources and tools. The audit will be impossible without them.

• CDN analytics (Cloudflare, Fastly, AWS CloudFront, Akamai) for cache hit/miss counts and edge request logs.
• Origin access logs and application logs (NGINX, Apache, Varnish, S3) for origin fetch rates.
• Real-user metrics (RUM) and synthetic tests that include cache-impacting headers.
• Basic CLI tools: curl, jq, awk, and a log query tool or ELK/Vector/ClickHouse access.
• Access to CI/CD pipelines and any tooling that triggers purges or deploy-time cache controls.

Step-by-step cache audit checklist (technical)

Run these steps in order. Each step finishes with concrete checks and remediation actions.

1) Discovery: Inventory cache surfaces

Map where caching happens across your stack: browser, CDN, edge workers, reverse proxies, origin caches, and application-level caches (Redis, Memcached).

• List all domains, subdomains, API endpoints, and static asset hosts.
• Identify which layer is authoritative for TTLs and invalidations.
• Note a set of high-traffic URLs and top conversion pages for focused analysis.

Deliverable: a table mapping host -> caching layers -> ownership.

2) Measurement: Baseline cache hit rate and origin load

Measure current hit rate and origin request reduction. Use both CDN-provided metrics and origin logs.

• From CDN analytics, grab edge hit, miss, and pass counts for the last 30 days.
• From origin logs, compute origin requests per day for the same period.
• Calculate cache hit rate: hit rate = hits / (hits + misses).

Example (Cloud CDN CSV):
hits = 1_200_000
misses = 300_000
hit_rate = hits / (hits + misses) = 80%
  

Quick log query (origin NGINX access log) to estimate cache pass behavior:

awk '{print $9}' access.log | sort | uniq -c | sort -nr | head

Deliverable: a dashboard with 7/30/90-day hit rate, origin requests, and bandwidth saved.

3) Header hygiene and canonical cache policy

Inspect HTTP response headers for the priority URLs. Run curl to fetch headers and verify expected cache-control semantics.

curl -I -s -H 'Accept: text/html' 'https://www.example.com/page' | sed -n '1,40p'

Key headers to audit:

• Cache-Control: max-age, s-maxage, immutable, public/private, must-revalidate, stale-while-revalidate, stale-if-error.
• Expires: avoid conflicts with Cache-Control; prefer Cache-Control in modern stacks.
• Vary: ensure it is limited to required values (Accept-Encoding, Cookie, Authorization, User-Agent). Excessive Vary fragments cache effectiveness.
• Surrogate-Key/Surrogate-Control/Cache-Tag: used for targeted invalidation in CDNs and reverse proxies.
• Age and X-Cache headers: validate whether responses are served from edge cache.

Common problem: HTML responses flagged as private or contain Set-Cookie, preventing CDN caching. Fix by scoping Set-Cookie to authentication endpoints only and using token-based microcookies where needed.

4) TTL strategy: classify and assign

Create a TTL matrix aligned to business value, update frequency, and cache risk. Give the most traffic-heavy, low-change assets the longest TTLs.

• Static assets (images, JS, CSS): 1 week to 1 year with cache-busting via content-hash filenames.
• CDN-shared assets (popular assets): 1 day to 30 days depending on change cadence.
• HTML pages: use shorter TTLs (minutes to 1 hour) plus stale-while-revalidate to avoid blocking users while background revalidation occurs.
• APIs: cache safe responses with contextual keys and short TTLs (seconds to minutes) where data is read-heavy.

Example HTTP header for HTML with revalidation:

Cache-Control: public, max-age=60, stale-while-revalidate=30, stale-if-error=86400

Deliverable: TTL matrix mapped to routes, and a rollout plan to apply TTLs via CDN rules or origin headers.

5) Cacheability review: page-level and fragment caching

Not all content can be full-page cached. Identify where fragment caching, Edge Side Includes (ESI), or streaming can unlock cache hits for pages with small dynamic parts.

• Look for personalized banners, cart counts, or user-specific widgets. Convert to client-side hydration or fragment include that fetches data via a short-lived API.
• Consider ESI or edge functions to assemble cached fragments with personalized micro-requests.
• Use surrogate keys on fragments and publish targeted purges on content changes.

Example Varnish VCL snippet assigning surrogate key:

sub vcl_deliver {
  if (resp.http.X-Cacheable == 'yes') {
    set resp.http.Surrogate-Key = "article-123 author-456";
  }
}

Deliverable: list of pages converted to fragment caching and estimated hit rate improvement.

6) Invalidation and purge workflows

Audit current invalidation mechanisms. Common issues: manual purges, over-broad purges, no CI integration.

• Prefer targeted invalidation (surrogate keys, tags) over global cache clears.
• Integrate purge operations into CI/CD for content and code deploys to ensure cache coherence.
• Rate-limit and audit purge requests; provide an approvals process for large purges.

Example: Cloudflare API purge by tag or key (conceptual):

POST /zones/:zone_id/purge_cache
{
  'files': ['https://assets.example.com/app.abc123.js']
}

Deliverable: automated purge playbooks and CI hooks plus a rollback plan for mistaken purges.

7) Edge functions and compute interactions

Edge compute changed the game: functions can generate HTML at the edge but can also accidentally bypass caches. Audit all edge workers/functions.

• Ensure edge functions set appropriate Cache-Control or use cache APIs provided by the CDN.
• Detect cold-start or per-request requests to origin caused by function logic that varies on headers unnecessarily.
• For Next.js-style frameworks, confirm ISR / On-Demand Revalidation is implemented with targeted purges rather than forcing full re-rendering per user.

Deliverable: map of edge functions and recommended cache API use or isolation for non-cacheable logic.

8) Observability and SLA for cache health

Make cache health observable: synthesize metrics and set SLOs for hit rate, origin failure rate, and purge latency.

• Essential metrics: edge hits, misses, pass rate, origin fetch latency, 4xx/5xx responses from origin, purge propagation time.
• In 2026 many teams instrument caches with OpenTelemetry traces that attach cache tags to span metadata — adopt this to correlate cache behavior with user-perceived latency.
• Set alerts for sudden hit-rate drops (e.g., >10% drop in 30 minutes) and for origin traffic spikes after deploys.

Deliverable: dashboard, alerts, and runbook for cache incidents.

9) Governance: roles, runbooks, and cost controls

Define who can purge, change TTLs, and approve targeted caching rules. Create a small governance policy and tie to deploy approvals.

• Lock production cache controls behind role-based access and change windows where appropriate.
• Create budget alerts for egress / bandwidth to detect cache regressions causing billing spikes.

Deliverable: policy doc, access matrix, and Slack/incident channels for cache ops.

Hands-on checks and commands (practical)

Use these concise, actionable checks during the audit.

1. Check whether a response is cached at the edge:

curl -I -s 'https://www.example.com/page' | egrep -i 'Cache-Control|Age|X-Cache|X-Served-By|Via'

2. Measure TTL being enforced across layers (repeat requests and inspect Age):

curl -s -D - 'https://www.example.com/page' -o /dev/null
# wait 10s
curl -s -D - 'https://www.example.com/page' -o /dev/null
# Age header should reflect seconds since edge cached the resource

3. Estimate percent of origin traffic saved using simple math:

origin_requests_before = 1_000_000
estimated_savings_pct = hit_rate
origin_requests_after = origin_requests_before * (1 - hit_rate)

Common problems and targeted fixes

These are recurring issues found during audits and exact remediation patterns.

• Problem: HTML pages not cached — often due to Set-Cookie or Authorization headers. Fix: limit cookies to auth endpoints, render public portions at edge, use personalized JavaScript fetches for private bits.
• Problem: Excessive Vary headers — reduces cache reuse. Fix: remove unnecessary Vary values and normalize user-agent variants at the application layer.
• Problem: Global purges after content changes — kills cache and spikes origin costs. Fix: use surrogate keys/tags for targeted purge and integrate with CMS webhooks.
• Problem: Edge functions bypassing caches — functions return dynamic headers. Fix: explicitly set cache API calls and use background revalidation patterns.

Benchmarks & ROI — what to expect

Based on industry audits in 2025–2026, realistic outcomes from a focused cache audit and implementation:

• Static asset bandwidth reduction: 70–95% for well-hashed assets.
• HTML origin request reduction: 30–70% after fragment caching and stale-while-revalidate.
• TTFB improvement: 20–60% for cached pages at edge vs origin.
• Conversion uplift: 5–25% for pages where core web vitals improved materially and content is cache-coherent.

Quick ROI formula:

Monthly bandwidth_saved = total_bandwidth * hit_rate_improvement
Monthly_cost_savings = bandwidth_saved * egress_cost_per_GB

Automation: enforce cache policy in CI/CD

Automate cache rules in deploys to avoid configuration drift.

• Store canonical cache headers as code (YAML/JSON) and apply via IaC to CDNs (Terraform + provider plugin) and origin deploy scripts.
• On deploy, run a smoke-test script that validates sample URLs for expected Cache-Control and Age behaviors; fail the pipeline on regressions.
• Publish change logs for cache rule updates and tie to feature flags to enable quick rollbacks.

Example CI check step (pseudo):

script:
  - curl -I https://www.example.com/page | grep 'Cache-Control: public, max-age=60'
  - if [ $? -ne 0 ]; then exit 1; fi

Future-proofing: trends to watch (2026+)

Keep these developments in scope for future audits:

• Privacy-driven partitioned caches — browser privacy features may further partition caches; design caching so critical assets remain cacheable in first-party contexts.
• ML-driven TTL tuning in CDNs — providers will suggest TTLs based on traffic patterns; validate suggestions against business risk.
• Edge service mesh — orchestration of distributed edge functions will require standardized cache observability traces.
• Standardization — expect increased adoption of cache tag standards (Surrogate-Key patterns) making cross-CDN invalidations easier.

"Think of cache audits like SEO audits: prioritize the high-impact pages, measure, and repeat."

Audit template: one-day actionable plan

Use this condensed timeline to run a practical audit in one day.

• Hour 0–1: Inventory hosts and gather analytics.
• Hour 1–3: Baseline hit rate and identify top offenders (pages with low hit rate but high traffic).
• Hour 3–5: Header inspection and quick fixes (remove Set-Cookie, add s-maxage, add stale-while-revalidate where safe).
• Hour 5–7: Implement targeted TTL changes and surrogate keys; add CI smoke checks.
• Hour 7–8: Instrument dashboards and set alerts; write a short runbook.

Final checklist (printable)

• Collect CDN and origin logs
• Compute current cache hit rate
• Inspect headers for top URLs
• Apply TTL matrix and fragment caching where applicable
• Replace global purges with surrogate-key invalidation
• Integrate cache checks in CI/CD
• Set SLOs and alerts for cache metrics
• Document roles and purge governance

Closing: actionable takeaways

• Prioritize fixing cacheability and header hygiene for pages that drive traffic and conversions.
• Measure before you change: baseline hit rate and origin load to quantify impact.
• Move from ad-hoc purges to targeted invalidation with surrogate keys and CI integration.
• Make cache health observable with dashboards and alert SLOs — treat cache as part of your production SLA.

Call-to-action

Run this audit on a high-traffic property this week. If you want a turnkey checklist and CI templates tailored to your stack (Cloudflare, Fastly, CloudFront, NGINX, Varnish), download our audit kit or contact our team for a 90-minute cache health session to convert cache wins into measurable traffic and cost savings.

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