Alloy is a language for describing structures and a tool for exploring them. It has been used in a wide range of applications from finding holes in security mechanisms to designing telephone switching networks.

An Alloy model is a collection of constraints that describes (implicitly) a set of structures, for example: all the possible security configurations of a web application, or all the possible topologies of a switching network. Alloy’s tool, the Alloy Analyzer, is a solver that takes the constraints of a model and finds structures that satisfy them. It can be used both to explore the model by generating sample structures, and to check properties of the model by generating counterexamples. Structures are displayed graphically, and their appearance can be customized for the domain at hand.

At its core, the Alloy language is a simple but expressive logic based on the notion of relations, and was inspired by the Z specification language and Tarski’s relational calculus. Alloy’s syntax is designed to make it easy to build models incrementally, and was influenced by modeling languages (such as the object models of OMT and UML). Novel features of Alloy include a rich subtype facility for factoring out common features and a uniform and powerful syntax for navigation expressions.

Alloy is a product of the Software Design Group at MIT.

alloy team members

former team members

Major contributions to earlier versions of Alloy were made by: Felix Chang, Jonathan Edwards, Robert Seater, Derek Rayside, Greg Dennis, Ilya Shlyakhter, Mana Taghdiri, Mandana Vaziri, Sarfraz Khurshid, and Manu Sridharan.


Alloy is the product of a research project funded by the National Science Foundation under Grant Nos. 0325283, 0541183, 0438897 and 0707612; by the Air Force Research Laboratory (AFRL/IF) and the Disruptive Technology Office (DTO) in the National Intelligence Community Information Assurance Research (NICIAR) Program; and by the Nokia Corporation as part of a collaboration between Nokia Research and MIT CSAIL.