Common Expression Language (CEL)

CEL is an embeddable expression language from Google, designed for fast, portable, and safe expression evaluation in performance-critical applications. It is non-Turing complete and can only access data explicitly provided by the host application.

The language targets predicate logic and simple data transformations, with evaluation times in the nanosecond-to-microsecond range. Expressions compile once and evaluate repeatedly at negligible cost — ideal for patterns like security policy checks on HTTP requests, API filter expressions, and protocol buffer validation.

CEL is open source, with its specification and implementations hosted at github.com/google/cel-spec. It is already used across multiple Google and external systems.