cel-expr/cel-go

cel-go is a Go implementation of the Common Expression Language, a non-Turing complete expression evaluator designed for simplicity, speed, safety, and portability.

CEL solves the problem of safely evaluating untrusted expressions without the overhead of a full scripting language. The tool uses a three-phase approach: first, you define an environment by declaring which variables and functions should be available to expressions; second, you parse and optionally type-check expressions ahead of time to produce a stateless, thread-safe, cachable program; third, you evaluate that compiled program against input data. The language has C-like syntax that reads nearly identically across C++, Go, Java, and TypeScript, making expressions portable across platforms. Type-checking is optional but strongly encouraged, as it uses static analysis to reject semantically invalid expressions and produces metadata that improves performance during evaluation.

CEL is well-suited for scenarios where you need to evaluate user-supplied or configuration-driven expressions in a sandboxed environment without the resource cost of a full scripting language. It supports primitive types, lists, maps, JSON, and Protocol Buffers natively. The tool includes optional macros that expand at parse time, providing bounded iteration and fold operators like all, exists, exists_one, filter, and map for working with collections, as well as a has macro for unified field presence testing across protobuf and dynamic types. This approach avoids adding syntactic complexity to the core language while enabling powerful features.

The project maintains a steady stream of refinements and bug fixes. Development shows consistent attention to performance optimization and correctness, with regular updates addressing edge cases and improving the evaluation pipeline. The maintainers actively engage with the community on design questions and implementation details, particularly around type-checking behavior and macro expansion semantics.