# CEL Reference

Embedded computation with the common expression language runtime.

Source: https://www.twisp.com/docs/reference/cel

Twisp uses the [Common Expression Language](https://github.com/google/cel-spec) extensively for computation.

Anywhere the Expression type is used in GraphQL, a CEL expression is accepted and will be evaluated at runtime.

- [Variables Reference](/docs/reference/cel/variables): Context variables available in indexes, calculations, and tran codes.
- [Functions and Examples](/docs/reference/cel/examples): Comprehensive examples of functions provided by the runtime.
- [Functions](/docs/reference/cel/functions): Standard library functions provided by the runtime.