Varnish VCL Generator

Generate a Varnish 4.1 VCL with a health-checked backend, a PURGE ACL, paths that are never cached, tracking parameters stripped, cookie handling and grace mode.

Free · No sign-up · Your inputs stay in your browser

Input

Generate a Varnish VCL

Backend hostBackend portDefault TTL (s)Used when the backend sends no Cache-Control.Grace (s)How long a stale page may be served while refreshing, or while the backend is down.

Never cache paths starting withAllowed to PURGEStrip utm_, gclid and fbclid from the cache key

Output

default.vcl

1,802 characters

vcl 4.1;

import std;

backend default {
    .host = "127.0.0.1";
    .port = "8080";
    .first_byte_timeout = 60s;
    .probe = {
        .url = "/up";
        .interval = 5s;
        .timeout = 2s;
        .window = 5;
        .threshold = 3;
    }
}

acl purge {
    "127.0.0.1";
    "10.0.0.0"/8;
}

sub vcl_recv {
    if (req.method == "PURGE") {
        if (!client.ip ~ purge) { return (synth(405, "Not allowed")); }
        return (purge);
    }
    if (req.method != "GET" && req.method != "HEAD") { return (pass); }
    if (req.url ~ "^(/c0ns0le|/admin|/login|/cart|/checkout)") { return (pass); }
    if (req.http.Authorization) { return (pass); }

    # Tracking parameters do not change the page; drop them from the cache key
    set req.url = regsuball(req.url, "(\?|&)(utm_[a-z]+|gclid|fbclid|mc_[a-z]+)=[^&]*", "\1");
    set req.url = regsub(req.url, "(\?|&)+$", "");
    set req.url = regsub(req.url, "\?&", "?");

    # Static files never depend on cookies
    if (req.url ~ "\.(css|js|png|jpe?g|webp|avif|svg|woff2?|ico)(\?.*)?$") {
        unset req.http.Cookie;
        return (hash);
    }

    # Keep only the session cookie; anonymous visitors then share one cached page
    if (req.http.Cookie !~ "(laravel_session|wordpress_logged_in|PHPSESSID)") {
        unset req.http.Cookie;
    }
}

sub vcl_backend_response {
    set beresp.grace = 3600s;
    if (beresp.http.Set-Cookie || beresp.http.Cache-Control ~ "(private|no-store)") {
        set beresp.uncacheable = true;
        set beresp.ttl = 120s;
        return (deliver);
    }
    if (beresp.status == 200 && !beresp.http.Cache-Control) {
        set beresp.ttl = 300s;
    }
}

sub vcl_deliver {
    set resp.http.X-Cache = if (obj.hits > 0, "HIT", "MISS");
    unset resp.http.Via;
    unset resp.http.X-Varnish;
}

Cookies are what usually stop Varnish from caching anything: a request with any Cookie header is passed by the built-in VCL, and analytics sets one on every visitor. This keeps only the session cookie, so logged-out traffic is cached and logged-in traffic is not. Test with varnishd -C -f default.vcl, and watch hit rates with varnishstat.

Runs in this browser. Nothing you paste is sent to a server.

About this tool

Method, assumptions, practical next steps, and limits.

Cookies decide your hit rate

Varnish's built-in logic passes any request with a Cookie header and refuses to cache any response with Set-Cookie. Analytics and consent banners set cookies for every visitor, so without cookie handling nothing is cached. Keeping only the session cookie, as this VCL does, caches logged-out traffic and passes logged-in traffic. The hit rate guide explains the built-in rules.

Grace keeps the site up

With grace, Varnish serves a stale object while it fetches a fresh one in the background, and keeps serving it if the backend is down, within the grace period.

Frequently asked questions

How do I check a VCL for errors?

varnishd -C -f default.vcl compiles it and prints the generated C or the first error. Load it on a running instance with varnishadm vcl.load and vcl.use.

How do I see whether a request was a hit?

The X-Cache header added in vcl_deliver shows HIT or MISS. varnishstat shows the hit ratio, and varnishlog shows why a request was passed.

Is what I paste sent anywhere?

No. The tool runs entirely in your browser with JavaScript. Nothing you type or paste is sent to our server or stored.

Varnish VCL Generator

Generate a Varnish VCL

default.vcl

Cookies decide your hit rate

Grace keeps the site up

Frequently asked questions

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