Copilot is a realtime programming language and Runtime Verification framework. It allows users to write concise programs in a simple but powerful way using a stream-based approach.

Programs can be interpreted for testing, or translated C99 code to be incorporated in a project, or as a standalone application. The C99 backend ensures us that the output is constant in memory and time, making it suitable for systems with hard realtime requirements.

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-- Raw temperature from sensor, range -50.0C to 100.0C.
temp :: Stream Word8
temp = extern "temperature" Nothing

-- Transform the temperature to Celsius.
ctemp :: Stream Float
ctemp = (unsafeCast temp) * (150.0 / 255.0) - 50.0

-- Bind two triggers with a 3.0C hysteresis.
spec = do
  trigger "heaton"  (ctemp < 18.0) [arg ctemp]
  trigger "heatoff" (ctemp > 21.0) [arg ctemp]


Release 3.16 – 2023-07-07

We are pleased to announce the release of Copilot 3.16, a stream-based DSL for writing and monitoring embedded C programs, with an emphasis on correctness and hard realtime requirements. Copilot is typically used as a high-level runtime verification framework, and supports temporal logic (LTL, PTLTL and MTL), clocks and voting algorithms.

Among others, Copilot has been used at the Safety Critical Avionics Systems Branch of NASA Langley Research Center for monitoring test flights of drones.

This release introduces two important changes. The first is a battery of tests for the C99 backend. This contribution is a key component towards meeting the requirements of NASA’s Procedural Requirements for Research and Technology Software. The second is a breaking change in copilot-language: a type has moved modules.

Details are available here and here.

Current emphasis is on improving the codebase in terms of stability and test coverage, removing unnecessary dependencies, hiding internal definitions, and formatting the code to meet our new coding standards. Users are encouraged to participate by opening issues and asking questions via our github repo.


Copilot is distributed under the BSD-3-Clause licence, which can be found here.


We are grateful for NASA Contract NNL08AD13T to Galois, Inc. and the National Institute of Aerospace, which partially supported this work.

Additionally NASA Langley contracts 80LARC17C0004 and NNL09AA00A supported further development of Copilot.

We would like to thank Kaveh Darafsheh (NASA Langley Research Center) for his help with testing Copilot. In addition numerous people have helped with smaller things, reporting bugs etc. Thanks to all of them!