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This page refers to an older version of CosmoSIS. The new repository is now at with documentation at


Welcome to CosmoSIS.

CosmoSIS is a cosmological parameter estimation code. It is now at version 1.6

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.

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


Survey-specific code


Get help