Companies Using RackCache

I run the crawler that stores the response headers of every domain we visit, and RackCache is the clearest case I know of a header that belongs to a platform. Our October 2026 crawl counts 15,493 domains sending X-Rack-Cache, 6th of 12 in Caching with 0.55%, and 4,661 matched to a company. On 16 October 2026 I re-requested a random 600 from the clean set, slowly enough to get past ClickFunnels' rate limits, and grouped them by address, DNS and response headers.

What the header means

Rack::Cache is a Ruby gem that caches HTTP responses in front of a Rack app; its README calls it a drop-in component for apps that send freshness and validation headers. The header's value is a trace: miss, fresh, pass, stale, valid, store. Any value means a Ruby app, usually Rails, answered. Nothing in it says who runs the app.

Sales signal: a RackCache domain is a Ruby-served page. Whether that's the owner's Rails team or a platform is the first thing to find out.

ClickFunnels writes most of it

342 of the 600 (57.00%) pointed at ClickFunnels: a CNAME to target.clickfunnels.com, one of the five Cloudflare addresses that name resolves to, a redirect into a ClickFunnels page or its page code. Across the whole clean set our ClickFunnels signal shows on 61.61%. The titles read like funnels: webinar sign-ups, free guides, coaching offers. These are ClickFunnels customers, real businesses with real pages, but none of them chose Rack::Cache.

"Six in ten RackCache domains are ClickFunnels funnel pages. The cache is part of ClickFunnels' servers, and the site owner bought a funnel builder." - David Thomson, CTO at TechnologyChecker.io

Sales signal: treat the majority as a ClickFunnels customer list: coaches, marketers and small online businesses. Pitch marketing tools, not infrastructure.

Where GoDaddy fits

GoDaddy co-detects on 35.36% of the clean set, which makes it look like a host. Our GoDaddy signal reads name servers and mail records, though, and 4,056 of the 5,454 domains with it are ClickFunnels pages. In the sample, 145 of the 342 ClickFunnels domains used GoDaddy's name servers: people who bought a domain at GoDaddy and pointed it at ClickFunnels.

Sales signal: GoDaddy here is the registrar. Domain, email and DNS offers fit; hosting offers don't.

The other Ruby platforms

The rest of the sample is a short list of Rails platforms: NationBuilder 32, Jane's clinic websites 29, Demosphere's youth-soccer sites 12, CrystalCommerce game stores 11, VersaCommerce shops 8, Cyberbiz stores 6. Action Network's union and campaign pages and Teamtailor's career sites appear in the company list. Self-run Rails apps are smaller than they look: 36 on Phusion Passenger, 13 on Heroku, and part of the 104 I couldn't assign. That's where Crunch's member portal, Metalsa's investor site and the European Southern Observatory's recruitment portal sit.

Sales signal: the self-run slice, 49 confirmed domains in the sample plus part of the 104 unassigned, is the only part with a Rails team you can talk to. Ruby hosting, monitoring and security tools belong there.

How much of it is live

466 of the 600 (77.67%) sent the header on the day. 80 (13.33%) were ClickFunnels domains that now fail: 55 return Cloudflare's 403 and 25 its "CNAME Cross-User Banned" error, both signs that no funnel is connected any more. 29 more didn't answer. Our title census sees only 42 placeholder or error titles (0.27%), because these pages died after our crawl or answer with a bare error. A failed fetch doesn't change a domain's status, so they stay in the count.

Sales signal: about one ClickFunnels domain in four in the sample was dead. Check before you call.

Who the site owners are

69.64% of sized companies have 1 to 10 staff and 44.70% were founded in the 2010s. Industries follow the platforms: advertising services 6.18%, wellness and fitness 5.18%, medical practices 5.08%, spectator sports 4.63%, coaching 4.16%. The US has 2,159 matched companies, Canada 479 and New Zealand 149. Only 44 have more than 1,000 staff, and nearly all of them run a Rails app of their own on a subdomain rather than a funnel page.

Sales signal: read the industry chart as a platform chart. Coaching and advertising mean ClickFunnels, medical practices mean Jane, spectator sports mean Demosphere, political organisations mean NationBuilder or Action Network. Sell to each through its platform's marketplace or partner list.

Overlap and movement

We don't publish switching rows here. 169 domains run RackCache and Varnish today, 75 WP Rocket and 53 LiteSpeed Cache, mostly layers on one site. The monthly line went from 14,159 in June to 15,493 in October, partly because the domains we crawl turn over each month and our detection widens. 1,364 domains dropped the header on a hostname since 16 March 2026; 175 still send it elsewhere.

"Most RackCache domains that failed in our sample were ClickFunnels domains with no funnel attached. Those are switched-off funnels, nothing to do with a cache decision." - David Thomson, CTO at TechnologyChecker.io

Sales signal: dropped headers on ClickFunnels domains are lapsed funnels, which can mean a lapsed subscription.

What it costs

Rack::Cache is free, released under the MIT licence. RubyGems lists version 1.17.0, released 5 April 2024, with 62,933,123 downloads when I checked on 16 October 2026. The gem's repository now sits under the Rack organisation on GitHub. The money on this page goes to the platforms.

Key takeaways

1. 15,493 domains; 77.67% of a 600-domain sample still sent the header.

2. ClickFunnels is 61.61% of clean domains and 57.00% of the sample.

3. GoDaddy is the registrar behind many of them, not the host.

4. 13.33% of the sample were ClickFunnels domains with no live funnel.

5. Self-run Rails apps are a small slice, and the enterprise names live there.

How to use this list

Split it by platform first: ClickFunnels, NationBuilder and Action Network, Jane, Demosphere, then self-run Rails. Pair the self-run slice with our Ruby on Rails page, and see our guide to how we detect technologies for what a header can tell you. The full list of 15,493 domains, with 4,661 matched companies, is on TechnologyChecker.io.