How to find out what a website is built with, in bulk

The short answer

You can tell what a site is built with by looking at what it loads and what it returns in its headers. That is what every tech-lookup tool does, browser extensions included. The difference between them is not magic, it is how many signatures they check and how honest they are about confidence.

The free routes

View source. Genuinely effective. A Shopify store, a WordPress site or a Next.js app announces itself in the markup within about ten seconds of looking. Free, accurate, and completely unworkable past a handful of sites.

Browser extensions. One click, a readable panel, no cost. The same ceiling applies: it works per tab, and a list of five hundred domains is five hundred tabs.

Write your own fetch and match. The honest version of this project is a couple of afternoons: fetch the page, parse the headers, look for known paths, keep a signature list, and then keep that signature list current as frameworks change their fingerprints. It is the maintenance, not the first version, that is the work.

Three things that make the answer wrong

The homepage is not the site. Plenty of companies run a marketing page on one stack and the product on another. Checking only the root domain tells you what the marketing team chose.

A CDN hides the origin. Put a site behind a large CDN and many server-level signals disappear. A tool that then reports the CDN as the stack is technically right and practically useless.

Confidence is not binary. Some signals are conclusive, such as a framework-specific path that returns a known payload. Others are hints, like a class name convention. A result that presents both as the same certainty is the reason these tools get a reputation for being unreliable.

What people actually use this for

Two jobs, almost always. Lead qualification, because knowing that a prospect runs a specific e-commerce platform or marketing tool decides whether they are worth a conversation. And market research, because the share of a stack across a segment is a genuine answer to a genuine question.

Both need the same thing: a list in, one row per site out, the same signatures applied to every row so the comparison holds.

What we charge for it

Billed per site analysed at $50.00 per 1,000, five cents a site. That is the most expensive row in our catalogue, for the honest reason that it costs the most to produce: it is a real fetch with parsing across a signature set, not a lookup against a table.

If you need the pages themselves audited rather than the stack identified, the technical SEO audit is the neighbouring dataset, billed per page audited at $30.00 per 1,000, with the crawl and header checks per URL.

For a prospect list of two hundred companies that is ten dollars, once, and you get a column you can actually filter on. For one site, use the extension.