bazelbuild/starlark

Starlark is a configuration language designed for use in build systems and other applications that need embedded scripting capabilities.

Starlark addresses the need for a safe, deterministic, and parallelizable configuration language by providing a Python-like dialect with restricted execution semantics. The language is dynamically typed with high-level data types, first-class functions, and lexical scoping. Its core design enforces deterministic evaluation so the same code always produces identical results, hermetic execution that prevents access to the file system or network, and parallel module loading with immutable shared data to ensure thread safety. Applications embed a Starlark interpreter and extend it with domain-specific functions and types relevant to their use case.

Starlark suits projects that need configuration or scripting with safety guarantees, particularly build systems and tools that must execute untrusted or user-provided code without side effects. The language is intentionally small and simple, prioritizing readability and quick comprehension over feature richness. Its Python-like syntax reduces the learning curve for developers familiar with Python. The design emphasizes tooling support, recognizing that code will be read and analyzed by both humans and automated systems. Starlark was originally developed for the Bazel build tool, where it serves as the notation for BUILD files and as a macro language for extending Bazel with custom logic to support new languages and compilers.

The repository functions as a specification and discussion hub for the language rather than a single reference implementation. Multiple independent implementations of Starlark exist across different programming languages. The project maintains a formal specification document and design rationale, with ongoing discussions about language features and design choices. Development activity centers on language design decisions and specification refinement rather than implementation maintenance.