Fift

Fift is a domain-specific programming language and toolkit used in The Open Network (TON) blockchain project. It is designed for low-level scripting, data serialization, and tooling that interacts with the TON Virtual Machine. Fift is a stack-based, Forth-like language that runs within the TON tooling ecosystem and is used to create, manipulate, and verify the data structures that underlie TON messages, contracts, and wallets, most notably the Bag of Cells format used to represent serialized data.

Fift provides primitives for manipulating cells, integers, and byte arrays, and facilities to construct and inspect messages and code that run on the TON VM. It is widely used for building and testing transactions, encoding and decoding BOC data, and scripting routines that set up test states or perform validation of TON data. The language emphasizes determinism and portability, enabling developers to reproduce results across environments.

Originating as part of the TON project initiated by Telegram in 2018, Fift was released as part of the open-source TON toolkit after the project encountered regulatory issues. Since then, it has been maintained by the TON community and contributors such as TON Labs, alongside other tooling in the TON ecosystem.

Typical workflow involves authoring .fif source files and running the fift command-line tool to execute them, compile data into BOC, or generate code suitable for the TON Virtual Machine. The resulting outputs are used to prepare messages, deploy or test smart contracts, or verify protocol-level structures. Fift complements higher-level languages used in TON, such as Solidity-inspired contracts, by providing low-level data and message handling capabilities.