diff --git a/README.md b/README.md
index 33344dc..5c3d339 100644
--- a/README.md
+++ b/README.md
@@ -14,15 +14,32 @@ nix run github:DeterminateSystems/flake-checker
 nix run github:DeterminateSystems/flake-checker /path/to/flake.lock
 ```
 
-Nix Flake Checker looks at your `flake.lock`'s root-level [Nixpkgs] inputs and checks that:
+Nix Flake Checker looks at your `flake.lock`'s root-level [Nixpkgs] inputs.
+There are two ways to express flake policies:
+
+* Via [policy conditions](#policy-conditions) using [Common Expression Language][cel] (CEL)
+* Via [parameters](#parameters)
+
+## Policy conditions
+
+
+
+## Parameters
+
+and checks that:
 
 - Any explicit Nixpkgs Git refs are in this list:
-  - `nixos-23.11`
-  - `nixos-23.11-small`
-  - `nixos-unstable`
-  - `nixos-unstable-small`
-  - `nixpkgs-23.11-darwin`
-  - `nixpkgs-unstable`
+
+  * `nixos-23.11`
+  * `nixos-23.11-small`
+  * `nixos-24.05`
+  * `nixos-24.05-small`
+  * `nixos-unstable`
+  * `nixos-unstable-small`
+  * `nixpkgs-23.11-darwin`
+  * `nixpkgs-24.05-darwin`
+  * `nixpkgs-unstable`
+
 - Any Nixpkgs dependencies are less than 30 days old
 - Any Nixpkgs dependencies have the [`NixOS`][nixos-org] org as the GitHub owner (and thus that the dependency isn't a fork or non-upstream variant)
 
@@ -96,6 +113,7 @@ The `parse-flake-lock` crate doesn't yet exhaustively parse all input node types
 If you'd like to help make the parser more exhaustive, [pull requests][prs] are quite welcome.
 
 [action]: https://github.com/DeterminateSystems/flake-checker-action
+[cel]: https://cel.dev
 [detsys]: https://determinate.systems
 [flakes]: https://zero-to-nix.com/concepts/flakes
 [install]: https://zero-to-nix.com/start/install
diff --git a/src/condition.rs b/src/condition.rs
index f9ebc03..bf5526a 100644
--- a/src/condition.rs
+++ b/src/condition.rs
@@ -11,6 +11,7 @@ pub(super) fn evaluate_condition(
     flake_lock: &FlakeLock,
     nixpkgs_keys: &[String],
     condition: &str,
+    allowed_refs: Vec<String>,
 ) -> Result<Vec<Issue>, FlakeCheckerError> {
     let mut issues: Vec<Issue> = vec![];
     let mut ctx = Context::default();
@@ -19,6 +20,15 @@ pub(super) fn evaluate_condition(
 
     for (name, dep) in deps {
         if let Node::Repo(repo) = dep {
+            let allowed_refs: Value = Value::from(
+                allowed_refs
+                    .iter()
+                    .map(|r| Value::from(r.to_string()))
+                    .collect::<Vec<Value>>(),
+            );
+
+            ctx.add_variable_from_value("allowed_refs", allowed_refs);
+
             for (k, v) in nixpkgs_cel_values(repo) {
                 ctx.add_variable_from_value(k, v);
             }
diff --git a/src/flake.rs b/src/flake.rs
index c0b1a35..8d237b4 100644
--- a/src/flake.rs
+++ b/src/flake.rs
@@ -147,19 +147,29 @@ mod test {
 
     #[test]
     fn test_cel_conditions() {
+        let allowed_refs: Vec<String> =
+            serde_json::from_str(include_str!("../allowed-refs.json")).unwrap();
         // (n, condition, expected)
-        let cases: Vec<(usize, &str, bool)> =
-            vec![(0, "has(git_ref) && has(days_old) && has(owner)", true)];
+        let cases: Vec<(usize, &str, bool)> = vec![(
+            0,
+            "has(git_ref) && has(days_old) && has(owner) && has(allowed_refs) && allowed_refs.contains(git_ref) && owner == 'NixOS'",
+            true,
+        )];
 
         for (n, condition, expected) in cases {
-            let path = PathBuf::from(format!("tests/flake.cel.{n}.lock"));
+            let path = PathBuf::from(format!("tests/flake.cel.clean.{n}.lock"));
             let flake_lock = FlakeLock::new(&path).unwrap();
             let config = FlakeCheckConfig {
                 check_outdated: false,
                 ..Default::default()
             };
 
-            let result = evaluate_condition(&flake_lock, &config.nixpkgs_keys, condition);
+            let result = evaluate_condition(
+                &flake_lock,
+                &config.nixpkgs_keys,
+                condition,
+                allowed_refs.clone(),
+            );
 
             if expected {
                 assert!(result.is_ok());
diff --git a/src/main.rs b/src/main.rs
index 66f580a..a029aa2 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -179,7 +179,7 @@ fn main() -> Result<ExitCode, FlakeCheckerError> {
     };
 
     let issues = if let Some(condition) = &condition {
-        evaluate_condition(&flake_lock, &nixpkgs_keys, condition)?
+        evaluate_condition(&flake_lock, &nixpkgs_keys, condition, allowed_refs.clone())?
     } else {
         check_flake_lock(&flake_lock, &flake_check_config, allowed_refs.clone())?
     };
diff --git a/tests/flake.cel.0.lock b/tests/flake.cel.clean.0.lock
similarity index 100%
rename from tests/flake.cel.0.lock
rename to tests/flake.cel.clean.0.lock