// Simple predicates
'tacocat'.startsWith('taco')

// Parameterized predicates over structured data
account.balance >= transaction.withdrawal

// JSON objects
{'sub': '12345678',
 'aud': 'example2.cel.dev',
 'iss': 'https://example1.cel.dev/jwt-issuer'}

// Strongly typed objects
common.GeoPoint{ latitude: 10.0, longitude: -5.5 }

Common Expression Language (CEL) is an expression language that’s fast, portable, and safe to execute in performance-critical applications. CEL is designed to be embedded in an application, with application-specific extensions, and is ideal for extending declarative configurations that your applications might already use.

Use CEL for things like list filters for API calls, validation constraints on protocol buffers, and authorization rules for API requests.

Learn more Get started
Accelerated expression evaluation in performance-critical paths from nanoseconds to microseconds.
Developer friendly, light weight with common syntax across multiple Google and external systems.
Non-Turing complete, and only accesses data provided by the host application.
Prove correctness, safety invariants, and equivalence across all inputs using automated SMT solvers like Z3.

CEL is ideal for performance-critical applications because it was designed to evaluate safely and quickly (nanoseconds to microseconds) with predictible costs. CEL expressions are especially useful for predicate logic and simple data transformations.

CEL is used most efficiently in applications where expressions are evaluated frequently, but modified infrequently. For example, evaluating an HTTP request against a security policy is an excellent use case for CEL. A CEL security policy expression would have a one-time configuration cost for validating the expression and then be evaluated very frequently at a negligible cost.

Still not sure? Check out the CEL overview and language definition, or just ask us! We're happy to help.

CEL overview Language definition Ask our team

As AI agents author, refactor, and deploy policies, heuristic unit tests may fail to cover edge cases across infinite inputs. The CEL Formal Verification Framework, powered by the Z3 theorem prover, enables developers to mathematically prove policy correctness, check AST equivalence, and guarantee security invariants across the entire input space.

Catch subtle logic flaws, enforce exhaustive guardrails, and secure automated policy authoring with mathematical certainty.

Read the announcement CEL Java Verifier
Want to help the CEL project? Contribute to our open source code and documentation. We'd love your help!
Contribute