The 15 best website technology checkers and theme detectors

1. StackScan, the one that answers the question backwards

The free checkers further down this page all work the same way. One URL in, one answer out.

StackScan runs the question backwards.

You name a technology and it hands you the sites running it, drawn from an index of 360 million plus domains covering 55,000 technologies.

That inversion is the whole reason it sits at the top. Knowing what one site runs is curiosity. Knowing every site that runs something is a project, and barely a handful of tools on this page can attempt it.

Say you want every WooCommerce store in Germany that also loads Klaviyo. Or every site still running a page builder that stopped shipping updates two years ago. No single site checker will get you there.

WordPress coverage is the deepest here, and not because it reads more off any one page. Themes and plugins both sit in the catalogue, and because the index runs in reverse you can pull every site using a given plugin instead of testing them one at a time.

Three tools ship with it. Tech Lookup is the reverse search. Keyword Scan searches page copy by keyword or topic rather than installed software, which surfaces people circling a category before they buy into it. Stack Explorer reports adoption by technology and country so you can size a segment before spending on it.

Getting the data out is not a bottleneck either. There is a REST API, CRM integrations, Zapier and n8n, an MCP server for agent workflows, and CSV export carrying up to 20 data points per domain.

Plans open at $39 a month. Rebuilding the same report later does not burn a fresh credit, so watching a segment over time costs nothing after the first pull.

2. WhatRuns, one click and the whole stack

If you take one thing away from this page, take this one.

It lives in the toolbar. Click it on any page and the stack drops down.

Chrome and Firefox, no account, no daily ceiling, no charge.

For anyone working with WordPress the useful part is how far down it digs. It does not stop at naming the CMS. It reports the theme, then the plugins, and picks up fonts and CDNs on the way past.

Plugin level reporting is scarce. Most general detectors spot WordPress and consider the job finished.

New signatures land at a rate of 50 to 100 a day, so it ages better than free software usually does.

The limit is structural rather than a flaw. One page at a time, nothing to export, and no way to flip the question round.

3. WPThemeDetector, the most detail on the theme itself

This one is built for exactly the question we get asked.

Paste a URL, get the theme.

What sets it apart is how much it tells you about the theme once it finds it. Description, tags, licence, author, and a statistics box about the theme provider.

That last part matters more than it sounds. Knowing a site runs a child theme of some framework is useful. Knowing who built the parent, what licence it ships under, and how many sites use it tells you whether you can realistically get the same result.

It detects plugins as well, though not as many as ScanWP.

The interface is clean and there are no ads in the results, which is more than I can say for some of its competitors.

4. ScanWP, the best free plugin detection

Themes are the easy half. Plugins are where free tools usually give up.

ScanWP is the one that does not.

In head to head comparisons it consistently surfaces more plugins than IsItWP, and it has a larger theme database behind it.

That is the reason it sits above IsItWP here despite covering similar ground. When I have tested the same site in both, ScanWP came back with a plugin list and IsItWP came back with nothing.

It also runs separate detectors for Shopify and for hosting, so it is not strictly a WordPress tool.

The page carries advertising, which is the price of it being free.

5. IsItWP, the fastest yes or no

IsItWP does what the name says.

Paste a URL, find out whether it is WordPress, and get the host and theme if it can find them.

It is fast and it is free, and for the basic question it is fine.

Where it falls down is plugins. In comparison testing it has failed to find a single plugin on sites where ScanWP returned a full list.

The site is also a content and affiliate operation wrapped around the tool, so expect hosting recommendations alongside your result.

I still use it, because sometimes you only need to know whether you are dealing with WordPress at all before deciding which tool to open next.

6. W3Techs, for the question no single site answers

W3Techs does not inspect sites. It counts them.

A daily survey across the top 10 million websites, reported as market share across 24 categories.

Everything from the CMS and the web server down to the analytics, the host and the top level domain.

Detection leans on several thousand signals pulled from markup, JavaScript, stylesheets, URL patterns and response headers.

The much repeated claim that WordPress runs 43% of the web starts here, and you can watch that figure drift month by month.

Reading it costs nothing. Paid reports add trend history, growth rates and adoption among newly launched sites.

It will never tell you anything about one particular site, and the sample leans toward established domains, so newer and smaller sites are undercounted.

7. Netcraft, the one that remembers

Netcraft looks underneath the site rather than at it.

Server software, hosting provider, IP, nameservers, SSL certificate status, DMARC records.

It has been running since 1995, which gives it something none of the WordPress tools have. Hosting history.

You can see where a site was hosted three years ago and when it moved. For due diligence on an agency or a site you are about to buy, that history is worth more than the theme name.

Its June 2026 survey covered around 1.5 billion sites across 304 million domains.

It also carries security context, including phishing records and infrastructure risk signals, which is why security researchers use it more than marketers do.

Application layer detection is narrow. It will not name your theme or your plugins.

8. Wappalyzer, precise detection with an enterprise invoice

Wappalyzer began as an open source extension and still carries that engineering sensibility.

The catalogue runs to roughly 8,000 technologies, well short of BuiltWith's, but accuracy per detection is among the most dependable I have used.

Its API is the most pleasant to build against of anything here, by a comfortable margin.

That is the reason to pay for it. When code consumes the output rather than a person, this is the one to reach for.

Bulk lookups stretch to around 100,000 domains, and Salesforce and HubSpot apps come in the box.

The free extension plus roughly 50 free lookups a month let you audit accuracy before committing to anything.

Then you meet the price. $250 a month for a single seat, $450 for five seats with 20,000 API credits, $850 for enterprise.

For inspecting sites by hand it is hard to justify, because WhatRuns reports more WordPress detail and charges nothing for it.

9. BuiltWith, the only index with a long memory

Nothing here matches BuiltWith for breadth. Around 110,000 technologies across more than 250 million sites, reaching into obscure widgets and payment scripts other crawlers ignore.

Its genuine advantage is time.

It has been crawling for well over a decade, so it answers questions no younger index can. When did this site adopt that plugin. What did it replace. How long did it survive.

Chasing sites that have just abandoned a competing product? That archive is the entire proposition.

The bill follows accordingly. $295, $495 and $995 a month for Basic, Pro and Team on annual terms.

There is no usable free tier either. The public lookup is a shop window rather than an account, so you cannot test list building before paying.

10. NerdyData, search the source, not the label

NerdyData keeps the page source, which lets you search for literal strings rather than named products.

Any string at all.

An analytics ID. An affiliate parameter. A comment block from a theme you wrote yourself.

That last one matters if you build and sell themes. To find sites running your work without a licence, very little else will help.

The index is modest next to the leaders, roughly 20 million sites and a thousand or so technologies.

The price does not reflect that modesty. $200 a month for Basic, $300 per seat for Pro, $1,000 for a team.

11. SimilarTech, strong charts and a very quiet price list

SimilarTech has always been stronger on the aggregate picture than the individual record.

Which technologies are climbing, in which sectors and territories, and how sharply the curve bends.

When the output is a slide rather than a spreadsheet, that beats a list of domains.

What gives me pause is corporate rather than technical. The site now introduces itself as a Similarweb company and publishes no pricing at all.

Committing to a product midway through absorption into a larger platform carries real risk.

12. Similarweb, technology with traffic attached

Similarweb is a traffic estimation platform that happens to carry technology data.

That ordering matters. Nobody buys it for the tech detection.

What it adds is context the pure detectors lack. Knowing a site runs a given theme is one thing. Knowing it runs that theme and pulls two million visits a month is a different conversation.

For competitive research where traffic is the real question, it earns its place.

Traffic figures are modelled estimates, not measurements, and they get less reliable the smaller the site. For most WordPress sites the numbers are guesswork.

Pricing is quote based and lands well above anything else in the top half of this list.

13. Datanyze, a cheap extension that changed jobs

Datanyze was a serious technographic product once. ZoomInfo acquired it and steered it toward contact data.

The homepage headline is now Hot Contact Data on Cold Prospects, which tells you plainly where the attention went.

What remains is a Chrome extension surfacing company and contact details as you browse, on plans from roughly $29 to $55 a month.

If you pitch site owners for a living, having the contact attached to the stack saves you a step.

For working out what a site runs, the free tools higher up this page have overtaken it.

14. PredictLeads, data written for machines to read

PredictLeads is plumbing, and makes no attempt to be anything else.

Technology signals arrive alongside job postings, news events, funding rounds and company similarity, through an API, flat files, webhooks or MCP.

There is no dashboard worth the name, and that is deliberate.

The economics are what make it interesting at scale. A single credit returns as many as 1,000 technology detections for one company.

Enrich a table of 100,000 domains on a nightly schedule and that ratio decides whether the project is affordable at all.

You do need somebody willing to write the code that consumes it.

15. HG Insights, budgets rather than bytes

HG Insights is playing a different sport to everything above it.

Rather than reading public pages, it models corporate IT estates and spending across more than 25 million companies.

Not simply that an organisation runs something, but an estimate of the budget behind it.

No crawler sees past a corporate firewall. HG blends sources that are not crawls and approximates what sits behind one.

It ranks last purely on reach. Pricing opens near $31,000 a year, with no self-service route and no published rates.

None of this helps anyone trying to identify a theme. It is here so the top of the list has something to be measured against.