blekko Search Engine: Closed by IBM in 2015

By Bill Hartzer · Updated 27 October 2026

What blekko was, and where its results came from

blekko (styled in lower case) was a general web search engine that operated publicly from 1 November 2010 to 27 March 2015. It is listed here as no longer available: the public search service closed on the day IBM announced it had acquired blekko technology, and visitors to blekko.com were shown a single line, "The blekko technology and team have joined IBM Watson!"

While it ran, blekko belonged to the small and shrinking group of engines that genuinely answered queries from their own index (the engine's stored copy of the web, built by its own crawler). It did not resell Google, Yahoo or Bing. Had it survived, its verdict on this site would be own index, alongside Gigablast in its day and Mojeek today. That fact is often lost when blekko is remembered as an interface experiment: underneath the slashtags sat a real, independent index.

What set blekko apart was the philosophy applied to the index. Most engines trust one ranking algorithm over the whole web. blekko's pitch was curation against spam: human judgment about which sites count, applied on top of the crawl.

How the index and slashtags worked

blekko crawled the web itself and ranked the result itself. Two size figures survive, and they measure different things, so they should not be read as contradicting each other:

About 3 billion "trusted" pages in the index blekko actually served results from, per Wikipedia.
22 billion webpages across 140 million websites covered by blekko's ranking metadata, per Common Crawl's description of the data blekko donated to it in December 2012.

The gap between the two is the design in miniature. blekko scored a very large share of the web and then deliberately served from a much smaller, trusted subset. Coverage was traded for resistance to spam.

The mechanism for that trade was the slashtag: a named, curated list of sites that a query could be restricted to, written after a forward slash. A search such as cancer /health searched only the sites on the /health list, instead of the whole index. Lists were built by blekko's editors and by users. By blekko's own count, reported by Search Engine Watch in early 2011, human editors had created 110,000 slashtags.

Slashtags could also subtract. A "reverse slashtag" filtered a list out of the results rather than restricting results to it; the best known was -/contentfarms, which removed a list of content-farm sites from any query. Users could also mark an individual result as /spam, and those reports fed blekko's decisions about what to keep in the index at all.

blekko also exposed some of its ranking data publicly, including pages showing a site's inbound links and crawl data. Wikipedia records this transparency feature; it has not been independently verified for this page.

The content-farm ban of January 2011

blekko's most remembered act came in January 2011. Having offered the -/contentfarms filter, it went further and removed the worst-reported sites from its index entirely. Co-founder Rich Skrenta described the move as banning "the top 20 spam sites from blekko's index entirely, based on our users click /spam on results."

The targets were content farms: sites that publish very large volumes of cheaply produced articles written to match common search queries rather than to inform. Coverage at the time reported that one of the banned sites was among Demand Media's top revenue earners, and eHow is the name most widely given. The complete list of twenty was not recovered for this page, so which sites were on it beyond that report cannot be stated with confidence.

The timing is the reason the episode is still cited. Google's Panda algorithm update, which targeted the same class of thin, mass-produced content, followed in February 2011. That sequence is context, not causation: nothing in the record shows that blekko's ban prompted Panda. What it does show is that a small independent engine, using human curation and user reports, acted publicly on a problem weeks before the dominant engine did so algorithmically.

The ban also exposed the limit of the approach. Removing twenty sites by hand is a statement; doing the equivalent across billions of pages is not something an editorial staff can do.

Who ran it, and how it made money

blekko, Inc. was founded in 2007 in the San Francisco Bay Area by Rich Skrenta, its chief executive, with Bob Truel and Michael Markson. Skrenta had previously co-founded the Open Directory Project, originally launched as NewHoo, and the news aggregator Topix. The lineage matters: the Open Directory was a human-edited directory, and slashtags were in effect a directory's editorial judgment applied to a crawler-based index.

Wikipedia reports that blekko raised about $24 million in venture capital from U.S. Venture Partners and CMEA Capital, with angel investors including Marc Andreessen and Ron Conway. That figure has not been confirmed from a primary source and should be treated as reported rather than established.

The business model was structurally conventional: advertising on results, plus licensing of its data. No revenue figure has been found. The only usage number on record is self-reported: Search Engine Watch quoted blekko as saying that thirty million search queries were conducted on it in January. The article does not print the year; January 2011 is inferred from context. No later or independent usage figure was found.

In December 2012 blekko donated its search engine ranking metadata to the non-profit Common Crawl to help it avoid "webspam, porn, and excessive search engine optimization" when deciding what to crawl.

The IBM acquisition and the shutdown

On 27 March 2015 IBM announced that it had acquired "certain technology from Blekko, Inc." Financial terms were not disclosed. The same day the public search engine stopped serving results, and blekko.com displayed "The blekko technology and team have joined IBM Watson!" before redirecting to a post on IBM's Smarter Planet blog.

The two statements were not identical, and Search Engine Land noticed. IBM's wording, "certain technology," was narrower than blekko's homepage claim of "technology and team." What IBM bought, precisely, was never itemized publicly.

blekko was closed by acquisition rather than by a failure to raise money, which makes it unusual among independent engines of its generation. Its destination was IBM Watson, an enterprise technology business, and no public blekko-derived search engine followed.

What blekko.com does today could not be checked for this page: automated fetching was refused and the Internet Archive was not reachable. Its current behavior is unverified as of 27 October 2026.

What blekko got right, and what it could not do

What it got right was the diagnosis. In 2010 and 2011 the dominant complaint about web search was that results were filling with pages made for search engines rather than for readers. blekko said so plainly, built tools that let users act on it, and removed the worst offenders from its index before Google moved. Its slashtags also made ranking legible: a reader could see exactly which sites a /health search would consult.

What it could not do was scale curation. A slashtag is only as good as the people maintaining it, and 110,000 of them, many built by users, is a large surface to keep accurate. Serving from a trusted subset of about 3 billion pages meant that queries falling outside curated territory relied on a narrower index than the scale of the web suggested. And the user had to learn a syntax. Ordinary searchers type words, not /tags, so the feature that defined blekko was also the one most users never touched.

The honest summary is that blekko was a serious independent index with an interesting editorial layer, and a poor fit for anyone who wanted one search box to work without instruction. It is best remembered as evidence that human curation can beat an algorithm on a narrow problem, and that it cannot replace one across the whole web.

Common misconceptions

"blekko was a metasearch engine." No. It crawled and ranked its own index and did not resell another engine's results. Slashtags filtered blekko's own index; they did not pull results from elsewhere.

"blekko caused Google's Panda update." Unsupported. blekko's ban came in January 2011 and Panda in February 2011. The sequence is documented; a causal link is not.

"IBM bought blekko." Imprecise. IBM announced that it had acquired "certain technology from Blekko, Inc." blekko's own homepage said the technology and team had joined IBM Watson. Terms were never disclosed.

Frequently asked questions

Does blekko still exist?

No. blekko's public search engine closed on 27 March 2015, the day IBM announced it had acquired certain blekko technology. Searches were replaced by a message that the technology and team had joined IBM Watson, followed by a redirect to an IBM blog post. What blekko.com shows today could not be verified as of 27 October 2026.

Did blekko have its own index?

Yes. blekko crawled and ranked its own web index and did not resell Google, Yahoo or Bing. Wikipedia records about 3 billion trusted pages in the index it served from, and Common Crawl described blekko's ranking metadata as covering 22 billion pages across 140 million sites in December 2012. The two figures measure pages served and pages scored, so they do not conflict.

What were blekko slashtags?

Slashtags were curated lists of websites that a query could be limited to, typed after a slash. Searching cancer /health returned results only from sites on the /health list. Reverse slashtags such as -/contentfarms removed a list from results instead. Search Engine Watch reported in early 2011 that blekko's human editors had created 110,000 slashtags.

Why did blekko ban content farms?

Because its users reported them as spam. In January 2011 blekko removed what Rich Skrenta called the top 20 spam sites from its index entirely, based on users clicking /spam on results. Coverage reported that one was among Demand Media's top earners, with eHow widely named, but the full list was not recovered. Google's Panda update followed in February 2011.

Who founded blekko?

blekko was founded in 2007 by Rich Skrenta, its chief executive, with Bob Truel and Michael Markson. Skrenta had earlier co-founded the Open Directory Project, launched as NewHoo, and the news site Topix. Wikipedia reports about $24 million in venture funding from U.S. Venture Partners and CMEA Capital plus angel investors, a figure not confirmed from a primary source.

What did IBM do with blekko?

IBM announced on 27 March 2015 that it had acquired certain technology from Blekko, Inc. for its Watson business, with terms undisclosed, per an announcement relayed by IBM's counsel, Cravath, Swaine & Moore. blekko's homepage said both technology and team had joined IBM Watson. Search Engine Land noted that IBM's own wording was narrower. No consumer search product followed.

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