--- title: "How Does BuiltWith Work?" description: "How does BuiltWith work? It crawls public sites and matches page source, scripts, headers and DNS against a signature library to name each site's stack." canonical: https://jobspipe.dev/blog/how-does-builtwith-work date_published: 2026-09-09 date_modified: 2026-09-09 author: Dvir Atias --- # How Does BuiltWith Work? How does BuiltWith work? It crawls public sites and matches page source, scripts, headers and DNS against a signature library to name each site's stack. How does BuiltWith work? It crawls public websites on a schedule, then matches what it finds in the page source, HTTP headers, loaded scripts and DNS records against a library of technology signatures. Each match becomes a technology entry with first and last detected dates, so a domain lookup shows both a current stack and a history of changes. ## How does BuiltWith work, step by step? 1. **Crawl.** BuiltWith fetches the public pages of a domain the way a browser would, on a recurring schedule. It does not log in, so anything behind authentication is out of scope. BuiltWith publishes its own crawl size and coverage figures; treat them as vendor claims until you have checked a sample of domains you know. 2. **Fingerprint.** The fetched page is compared against signatures: a script path only Google Tag Manager uses, a cookie name set by one analytics vendor, a header a CDN adds, a meta tag a CMS writes, a nameserver or MX record that points at a hosting or email provider. A match is a detection. 3. **Keep history.** Detections are stored with first and last seen dates. That is how BuiltWith can report that a site added a tool one month and dropped another later, and it is the basis of its technology usage trend reports. 4. **Look up a domain.** The simplest use is the domain lookup: type a website and read the grouped report, from analytics and advertising through to hosting and frameworks. The browser extension does the same for the page you are on. 5. **Build a list.** The lists product lets you pick a technology, add filters such as country, traffic tier or vertical, and export the matching domains. This is the sales and lead generation use, and the one most people pay for. 6. **Query the API.** The domain API returns the same detections as JSON for one domain at a time, and the lists API returns domains for a technology. Pricing and rate limits are on BuiltWith’s own site and change, so check there rather than here. The method sets the limits. BuiltWith only sees what a public page exposes to a visitor. It cannot see the languages a backend is written in, the warehouse behind the dashboards, the internal tools engineers use, or the applicant tracking system unless the careers page loads it. It also reports a technology for as long as its fingerprint stays in the page, so an abandoned tag can linger as a detection. For a buyer that means BuiltWith is strong on the front-end, marketing and hosting layers and weak on everything that runs behind the load balancer. The [technographics](https://jobspipe.dev/technographics) page explains which layers each detection method covers, and [BuiltWith alternatives](https://jobspipe.dev/builtwith-alternatives) compares the tools side by side. Try it without a key ``` curl -d '{"limit":3}' https://api.jobspipe.dev/v1/sandbox/jobs/search ``` Only `/v1/sandbox/*` needs no key. ## Where JobsPipe fits JobsPipe is a jobs data API. It collects live postings from LinkedIn, Indeed, Y Combinator, Workday, Greenhouse, Workable, SmartRecruiters, Ashby, Lever and Paylocity, returns them as one schema with closure tracking and a ghost score, and includes a free tier of 1,000 jobs to start at [jobspipe.dev](https://jobspipe.dev). Job postings fill BuiltWith’s gap: an engineering posting names the languages, databases, cloud and data tools a team actually runs, whether or not any of them touch the public site. Scan a domain with `POST /v1/stack/scan` or the free [stack scanner](https://jobspipe.dev/stack), then confirm the backend with a posting search: ``` curl -X POST https://api.jobspipe.dev/v1/jobs/search \ -H "Authorization: Bearer $JOBSPIPE_API_KEY" \ -H "Content-Type: application/json" \ -d '{ "company_name_or": ["Shopify"], "status": "active", "limit": 25 }' ``` Every record carries `technology_slugs`, so the stack falls out of the results without a second tool. ## Frequently Asked Questions ### How to use BuiltWith Enter a domain in the lookup to get a grouped technology report, install the browser extension to read the page you are on, build a list by picking a technology and filters to export matching domains, or call the domain API for the same detections as JSON. Plans and limits are listed on BuiltWith's site and change over time. ### What can BuiltWith not detect? Anything a public page does not expose: backend languages, the data warehouse, internal tools, and the applicant tracking system unless the careers page loads it. It also cannot see pages behind a login, and a tag that is abandoned but still in the page keeps showing as a detection until it is removed. ### Is BuiltWith data accurate? It is accurate for what a page exposes at crawl time, which makes it reliable on analytics, advertising, CDN and CMS layers. Detections lag site changes and lingering tags inflate the list, so verify against a second source such as job postings before acting on a single domain's report. ### How do job postings complement BuiltWith? A company's job postings name the languages, databases, cloud services and data tools its teams run, which never appear in the public page. JobsPipe returns those as technology\_slugs on every posting, so a website scan plus a posting search covers both the front and the back of the stack. Related ## Keep reading - [Guide · Sep 9, 2026How Do Applicant Tracking Systems Work?](https://jobspipe.dev/blog/how-do-applicant-tracking-systems-work) - [Guide · Sep 9, 2026How Do Labor Markets Work?](https://jobspipe.dev/blog/how-do-labor-markets-work) - [Guide · Sep 9, 2026How Does MCP Work Under the Hood?](https://jobspipe.dev/blog/how-does-mcp-work-under-the-hood) - [Guide · Sep 9, 2026How Does Wappalyzer Work?](https://jobspipe.dev/blog/how-does-wappalyzer-work) - [Guide · Jul 13, 2026What is a SERP API? How they work and when to use one](https://jobspipe.dev/blog/what-is-a-serp-api) --- Try it with no key: `curl -d '{"limit":3}' https://api.jobspipe.dev/v1/sandbox/jobs/search`. AI agents: the full machine-readable index of this site is https://jobspipe.dev/llms.txt?src=md-twin - API quickstart, MCP server, pricing. Free key (1,000 jobs to start): https://jobspipe.dev/signup