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OpenCalais is the Open Source repository for the Calais project.

Mission Statement


"Calais: Connect. Everything."


We want to make all the world's content more accessible, interoperable and valuable. Some call it Web 2.0, Web 3.0, the Semantic Web or the Giant Global Graph - we call our piece of it Calais.

Calais is a rapidly growing toolkit of capabilities that allow you to readily incorporate state-of-the-art semantic functionality within your blog, content management system, website or application.




The free Calais Web service that has an open API. Users of the service can request 40,000 content transactions per day and a limit of 4 per second. Information and resources can be found at

Calais Professional

Is the same service as OpenCalais, but provides more transactions and 24×7 monitoring. The daily transaction count is increased to a maximum of 100,000 and a limit of 20 per second. Additional transactions can also be purchased.

Calais Professional for Publishers

Is the professional option for large scale publishers. It also has an option to purchase the service as an annual contract.

Calais Enterprise

Is the “enterprise software” version of Calais. Enterprises can install a customized version of Calais within the enterprise’s IT infrastructure. In addition to the functionality provided by the above options, enterprise users can create their own entities and relations in order to add information to the metadata that is generated by Calais.[2]



Gist is an up-to-date archive of news articles that have been passed through Clearforest (third-party tagging service). By applying user-input, business logic, metrics/analytics and advanced UI, we hope to gain greater insight and meaning from the chaotic, information-overload generally associated with the news.

Gist is not edited by any person, we rely solely on the volume of tags to determine our top stories -- so if you feel that the incorrect story is highlighted, check back in an hour or two.


Submit an article or other bulk text then watch it get magically marked up with Calais Metadata. The data can be shown as HTML with hover-triggered popups over the original text, or, as raw RDF data output.

Content Feed Explorer

Build a customized news feed with daily updated content and auto-tagging (available as RSS,mediaRSS,ATOM,JSON,RDF).



Calais Marmoset is a simple yet powerful tool that makes it easy for you to generate and embed metadata in your content in preparation for Yahoo! Search's new open developer platform, SearchMonkey, as well as other metacrawlers and semantic applications.

The Calais Microformats Injector provides a simple way to make your Web site's contents available through intelligent search.

OpenCalais Tags

OpenCalais Tags is a PHP class for extracting entities from text using Open Calais. Calais performs semantic analysis of the text, using natural language processing to identify concepts like people, companies and technologies discussed in the text. These are especially useful for suggesting tags for your content such as website articles or blog posts. You could even automatically tag archived content that would take days to go through manually.

Web Services

OpenCalais PHP Library

OpenCalais's general metadata repository has API access, along with demo code for working with the metadata from PHP, Java, C# and Ruby.

External Links


  1. OpenCalais Home:
  2. Reuters Leading the Semantic Web Charge:
  3. SemanticProxy -- API test tool:
  4. Try out OpenCalais's semantic analysis for yourself:

See Also

NLP | Semantic Web | OWL | RDF | XML | JSON