Find Companies Using Fastly: API Guide (2026)

Fastly is the CDN developers pick on purpose. Where some CDNs are switched on with a checkbox at a hosting provider, Fastly deployments involve edge configuration, VCL or edge-compute logic, and a team that cares about cache-hit ratios—which is exactly what makes “uses Fastly” a useful technographic filter. When the June 2021 Fastly outage briefly took large parts of the internet offline, the affected sites read like a who's-who of engineering-led companies: developer platforms, news publishers, package registries, and government portals. A Fastly-confirmed domain list skews toward companies with real traffic and a real platform team.

This guide covers what Fastly usage tells you about a company, the exact HTTP header and DNS signals that reveal it, and how to turn a raw domain list into a Fastly-confirmed lead list with the DetectZeStack API—starting with a keyless curl command you can run right now.

What Is Fastly and Why Track Who Uses It

Fastly is an edge cloud platform: a content delivery network built on Varnish, extended with programmable edge logic, instant cache purging, image optimization, and a WAF. Its pitch has always been control—developers write the caching rules themselves rather than clicking through a dashboard of presets. That positioning shapes its customer base, and the customer base is what makes the detection valuable:

• It signals an engineering-led organization. Fastly's configuration model assumes someone on staff is comfortable writing edge logic. A company running Fastly almost always has a platform or infrastructure team making deliberate CDN decisions—a strong qualifier if you sell developer tooling, observability, or infrastructure products.
• It maps the buyer. The Fastly relationship is owned by engineering or DevOps, not marketing. Knowing a prospect runs Fastly tells you which door to knock on and which pains resonate: cache strategy, origin offload, edge compute, multi-CDN failover, and delivery cost.
• It marks real traffic. Fastly is usage-billed and rewards high-volume, cache-friendly workloads. Media sites, API platforms, package registries, and high-traffic ecommerce are its natural fits—companies past the experimentation stage.

The same workflow applies to any CDN. We have companion guides for finding companies using Akamai and finding companies using Amazon CloudFront—the filter changes, the pipeline stays identical.

How Fastly Detection Works (Headers, DNS, and Edge Signatures)

Fastly is an infrastructure CDN: it sits in front of a site's origin and proxies every request, the same role Cloudflare, Akamai, and CloudFront play. Unlike a JavaScript library, it never appears in the page body—its evidence lives in the response headers its edge nodes stamp and in the DNS routing that sends traffic to those nodes. DetectZeStack checks both layers independently, so a match on either one confirms Fastly.

HTTP Header Signals (x-served-by, x-cache, via)

Run curl -sI against a Fastly-fronted site and the edge usually gives itself away. Two kinds of headers show up. The first group is generic Varnish-cache plumbing that Fastly's edge emits on most responses; the second group names Fastly explicitly and is what DetectZeStack's HTTP fingerprint matches at confidence 100:

One subtlety worth knowing: the loudest generic headers—via: 1.1 varnish and x-served-by—do not say “Fastly” anywhere in them, and the explicit fastly-* debug headers are not emitted by every service configuration. A self-hosted Varnish deployment produces a via: 1.1 varnish header too. That is why the DNS layer matters so much for this particular CDN.

DNS and CNAME Signals (fastly.net edges)

When a company points a custom domain at Fastly, the domain CNAMEs into Fastly's edge network rather than resolving straight to an origin IP. You can confirm it yourself with one dig:

$ dig www.example.com CNAME +short
example.map.fastly.net.

DetectZeStack follows the full CNAME chain a domain resolves through and matches the terminal hostname against Fastly's edge suffixes—fastly.net for the standard edge and fastlylb.net for load-balanced services. A match is reported under the CDN category with source: "dns" and confidence 80. DNS evidence is reliable but deliberately scored below a live header match, which returns 100. The mechanics of chain resolution are covered in DNS-Based Technology Detection, and the full multi-layer picture across every major CDN is in how to detect a website's CDN and hosting provider.

Check a Single Domain for Fastly with the DetectZeStack API

Try It Free with the /demo Endpoint

You can test detection right now against the public demo endpoint—no API key required. The demo is IP-rate-limited, so use it for spot checks rather than bulk scans:

$ curl -s "https://detectzestack.com/demo?url=example.com" \
  | jq '.technologies[] | select(.name == "Fastly" or .name == "Varnish")'
{
  "name": "Fastly",
  "categories": ["CDN"],
  "confidence": 80,
  "description": "",
  "website": "",
  "icon": "",
  "source": "dns",
  "version": "",
  "cpe": ""
}
{
  "name": "Varnish",
  "categories": ["Caching"],
  "confidence": 100,
  "description": "Varnish is a reverse caching proxy.",
  "website": "https://www.varnish-cache.org",
  "icon": "Varnish.svg",
  "source": "http",
  "version": "",
  "cpe": ""
}

This pair is the classic Fastly signature. The Fastly entry here came from the DNS layer—source: "dns", confidence 80, with description, website, icon, version, and cpe empty because that metadata is populated from HTTP fingerprints rather than the CNAME chain. The Varnish entry came from the via: 1.1 varnish header Fastly's edge added, matched at confidence 100 with full metadata. When a site's configuration emits the explicit fastly-* headers, the Fastly entry itself comes back with source: "http" and confidence 100 instead.

Confirm Fastly on a Domain with /check

When you only care about one yes-or-no question—does this domain use Fastly?—the /check endpoint returns a compact boolean instead of the full technology array:

$ curl -s "https://detectzestack.p.rapidapi.com/check?url=example.com&tech=Fastly" \
  -H "X-RapidAPI-Key: YOUR_KEY" \
  -H "X-RapidAPI-Host: detectzestack.p.rapidapi.com"
{
  "domain": "example.com",
  "technology": "Fastly",
  "detected": true,
  "confidence": 80,
  "version": "",
  "categories": ["CDN"],
  "response_ms": 743,
  "cached": false
}

The tech match is case-insensitive, and when Fastly is absent, detected is false with confidence 0. This is the endpoint for enriching an existing CRM one record at a time—a single uses_fastly column rather than the whole stack.

Build a Fastly Prospect List with /lookup and /analyze/batch

Two endpoints turn single-domain checks into lists. The first, GET /lookup, is a reverse index: it returns domains DetectZeStack has already observed running a technology, with no fresh scanning spent:

$ curl -s "https://detectzestack.p.rapidapi.com/lookup?tech=Fastly&limit=50" \
  -H "X-RapidAPI-Key: YOUR_KEY" \
  -H "X-RapidAPI-Host: detectzestack.p.rapidapi.com"
{
  "technology": "Fastly",
  "total": 214,
  "results": [
    {
      "domain": "example.com",
      "category": "CDN",
      "confidence": 80,
      "version": "",
      "first_seen": "2026-04-02T09:14:11Z",
      "last_seen": "2026-07-21T06:03:47Z"
    }
  ],
  "limit": 50,
  "offset": 0,
  "response_ms": 12
}

The first_seen and last_seen timestamps tell you how long each domain has been observed on Fastly. Results per request are capped by plan—2 on the free plan, 50 on Pro, 200 on Ultra, and 800 on Mega—and the limit and offset parameters page through them.

Batch-Scanning Your Own Domain List

When you already have a prospect list—a conference attendee list, a vertical you scraped, an existing CRM export—POST /analyze/batch scans it fresh. It accepts up to 10 URLs per request and analyzes them concurrently:

$ curl -s -X POST "https://detectzestack.p.rapidapi.com/analyze/batch" \
  -H "X-RapidAPI-Key: YOUR_KEY" \
  -H "X-RapidAPI-Host: detectzestack.p.rapidapi.com" \
  -H "Content-Type: application/json" \
  -d '{"urls": ["example.com", "fastly.com", "github.com"]}'

Each entry in the response wraps a full analysis result in the same shape as a single /analyze call, so the filtering logic is identical at any scale. Here is a complete, copy-pasteable pipeline using nothing but bash, curl, and jq. It reads domains.txt (one domain per line), sends batches of 10, and appends every Fastly-confirmed domain to fastly_leads.csv with its tech count:

#!/usr/bin/env bash
# find-fastly.sh — filter a domain list down to Fastly-confirmed leads
KEY="YOUR_KEY"
HOST="detectzestack.p.rapidapi.com"

echo "domain,tech_count" > fastly_leads.csv

# Process domains.txt in batches of 10 (the /analyze/batch maximum)
xargs -n 10 < domains.txt | while read -r batch; do
  urls=$(printf '%s\n' $batch | jq -R . | jq -s '{urls: .}')
  curl -s -X POST "https://$HOST/analyze/batch" \
    -H "X-RapidAPI-Key: $KEY" \
    -H "X-RapidAPI-Host: $HOST" \
    -H "Content-Type: application/json" \
    -d "$urls" |
  jq -r '.results[]
    | select(.result != null)
    | .result as $r
    | select([$r.technologies[].name] | index("Fastly"))
    | [$r.domain, ($r.meta.tech_count | tostring)]
    | @csv' >> fastly_leads.csv
done

wc -l fastly_leads.csv

A 1,000-domain list becomes 100 batch calls. The select(.result != null) guard skips domains that failed to resolve (those return an error field instead of a result). One reading note: because Fastly's DNS signal resolves whether or not the origin answers, a scan with meta.scan_depth of "partial"—meaning the HTTP fetch was blocked or timed out but DNS completed—can still confirm Fastly. An absent Fastly entry on a "full" scan is a genuine no. For batch throughput, retries, and a production Python scanner, see how to batch scan 1,000 websites.

Who Typically Runs Fastly: Common Stack Patterns

Once you have a Fastly-confirmed list, the rest of each domain's technologies array tells you what kind of company you are looking at. Patterns that show up repeatedly behind Fastly:

• Media and publishing. High article volume, aggressive caching, instant purge on story updates—Fastly's original sweet spot. These stacks pair the CDN with commercial analytics and ad-tech signals.
• Developer platforms and API companies. Package registries, documentation sites, and API-first products lean on Fastly for global static delivery. Expect modern JavaScript frameworks and few marketing pixels.
• Headless and high-traffic ecommerce. Storefronts that outgrew their platform's built-in delivery put Fastly in front for edge caching. The categories map makes this segmentation trivial: pull .categories["Ecommerce"] alongside the CDN entry.

Splitting your list on what sits behind the CDN turns one broad “uses Fastly” segment into precise sub-segments you can message differently—the same enrichment move detailed in tech stack enrichment for sales teams. Sorting by meta.tech_count is a rough but useful proxy for how built-out each company's stack is.

Fastly vs Other CDNs: Telling Them Apart

Each major infrastructure CDN leaves a distinct fingerprint, so a single scan cleanly separates them:

The ambiguous case is Varnish. A via: 1.1 varnish header alone could be Fastly's managed edge or a company running its own Varnish boxes—two very different prospect profiles. The disambiguation rule: Varnish plus a fastly.net CNAME or any explicit fastly-* header means a managed Fastly deployment; Varnish with neither usually means self-hosted, which signals a team that likes owning its own caching layer. We cover that second profile in find companies using Varnish. Some architectures also chain CDNs—Cloudflare in front for WAF, Fastly behind for caching—in which case DNS reveals the outer layer and headers can reveal the inner one; see the CDN detection guide for how multi-layer scanning catches both.

Get Started with an API Key

Every DetectZeStack plan includes header, DNS, and TLS detection—the Fastly matching described here runs on every request at every tier. Plans differ only in monthly request volume:

A /analyze/batch call counts each URL in the batch against your quota, so a 10-URL batch spends 10 requests. The free tier's 100 requests validate the pipeline on a sample of your list; a 10,000-domain scan fits inside the Ultra plan. Getting started takes three steps:

1. Get a key at rapidapi.com/mlugoapx/api/detectzestack—no credit card for the free tier.
2. Spot-check a domain you know runs Fastly: curl -s "https://detectzestack.com/demo?url=yourdomain.com" | jq '.technologies[].name'
3. Run the batch script above against your first 100 domains.

Conclusion

Finding companies using Fastly comes down to reading two layers well. The DNS layer catches the fastly.net and fastlylb.net CNAME chains at confidence 80, and the HTTP layer catches the explicit server: fastly and x-fastly-request-id headers at confidence 100—with the via: 1.1 varnish co-detection as the tell that separates managed Fastly from self-hosted Varnish. A single /check call answers the one-domain question, /lookup pulls domains already observed on Fastly, and /analyze/batch turns a raw prospect list into a Fastly-confirmed lead list. Because the signal spans two independent layers, it holds up whether a site strips its headers or hides its CNAME—and the same pipeline segments by any other CDN with a one-word change to the jq filter.