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Welcome to CosmoSIS.

CosmoSIS is a cosmological parameter estimation code. It is now at version 1.4

It is a framework for structuring cosmological parameter estimation in a way that eases re-usability, debugging, verifiability, and code sharing in the form of calculation modules.

It consolidates and connects together existing code for predicting cosmic observables, and makes mapping out experimental likelihoods with a range of different techniques much more accessible

CosmoSIS is described in Zuntz et al: - if you make use of it in your research, please cite that paper and include the URL of this repository in your acknowledgments. Thanks!


Webinar 1 recording and slides

Webinar 2 recording and slides

Mailing Lists

Sign up for the CosmoSIS announcements email list (for announcements by core team) by emailing with the subject line and message text: subscribe cosmosis_messages

Sign up for the CosmoSIS users email list (for discussion among users) by emailing with the subject line and message text: subscribe cosmosis_users

Install CosmoSIS

CosmoSIS needs a 64-bit operating system.

Try some short demos

These demos illustrate basic cosmosis concepts in action.

[The following are in development.]

Longer demos

These longer examples show realistic parameter constraint pipelines.


All the scientific code in CosmoSIS is organized into independent modules. CosmoSIS ships with a standard library of modules doing most standard cosmology calculations (stored in a separate repository), and if you want to build or modify a pipeline you can use them:

Input Files

A CosmoSIS run is specified with up two or three parameter files. The first two are required and the third (priors) is optional:

[In development] The further postprocessing stage, to produce graphical plots of the results, may be specified entirely on the postprocess command-line, or preferably in a file:


CosmoSIS comes with a range of samplers suitable for different likelihoods spaces.






Helper tools


Debugging modules

Libraries available to multiple modules


Survey-specific code


Discussions and meetings

Get help