diff --git a/app/cli/cmd/root.go b/app/cli/cmd/root.go
index 9784848b8..a9533516f 100644
--- a/app/cli/cmd/root.go
+++ b/app/cli/cmd/root.go
@@ -34,6 +34,7 @@ import (
 	"github.com/chainloop-dev/chainloop/app/cli/pkg/plugins"
 	v1 "github.com/chainloop-dev/chainloop/app/controlplane/api/controlplane/v1"
 	"github.com/chainloop-dev/chainloop/pkg/grpcconn"
+	"github.com/chainloop-dev/chainloop/pkg/policies/engine/rego/builtins"
 	"github.com/rs/zerolog"
 	"github.com/spf13/cobra"
 	"github.com/spf13/viper"
@@ -156,6 +157,11 @@ func NewRootCmd(l zerolog.Logger) *cobra.Command {
 
 			ActionOpts = newActionOpts(logger, conn, authToken)
 
+			// Add custom builtins to rego engine
+			if err = builtins.RegisterDiscoverBuiltin(conn); err != nil {
+				return fmt.Errorf("failed to register discover builtin: %w", err)
+			}
+
 			if !isTelemetryDisabled() {
 				logger.Debug().Msg("Telemetry enabled, to disable it use DO_NOT_TRACK=1")
 
diff --git a/pkg/policies/engine/rego/builtins/discover.go b/pkg/policies/engine/rego/builtins/discover.go
new file mode 100644
index 000000000..d3af9642f
--- /dev/null
+++ b/pkg/policies/engine/rego/builtins/discover.go
@@ -0,0 +1,101 @@
+//
+// Copyright 2025 The Chainloop Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package builtins
+
+import (
+	"errors"
+	"fmt"
+
+	v1 "github.com/chainloop-dev/chainloop/app/controlplane/api/controlplane/v1"
+	"github.com/open-policy-agent/opa/v1/ast"
+	"github.com/open-policy-agent/opa/v1/topdown"
+	"github.com/open-policy-agent/opa/v1/types"
+	"google.golang.org/grpc"
+)
+
+const discoverBuiltinName = "chainloop.discover"
+
+// RegisterDiscoverBuiltin is used to register chainloop's Discover endpoint as a builtin Rego function with signature:
+//
+//	chainloop.discover(digest, kind)
+//
+// For instance, to get the references for an CONTAINER_IMAGE material, and fail if any of them is an attestation with policy violations:
+// ```
+//
+//	violations contains msg if {
+//	  digest := sprintf("sha256:%s",[input.chainloop_metadata.digest.sha256])
+//	  discovered := chainloop.discover(digest, "")
+//
+//	  some ref in discovered.references
+//	  ref.kind == "ATTESTATION"
+//	  ref.metadata.hasPolicyViolations == "true"
+//
+//	  msg:= sprintf("attestation with digest %s contains policy violations [name: %s, project: %s, org: %s]", [ref.digest, ref.metadata.name, ref.metadata.project, ref.metadata.organization])
+//	}
+//
+// ```
+func RegisterDiscoverBuiltin(conn *grpc.ClientConn) error {
+	return Register(&ast.Builtin{
+		Name:        discoverBuiltinName,
+		Description: "Discovers artifact graph data by calling the Referrer chainloop service",
+		Decl: types.NewFunction(
+			types.Args(
+				types.Named("digest", types.S).Description("digest of the artifact to discover"),
+				types.Named("kind", types.S).Description("optional filter by kind to disambiguate"),
+			),
+			types.Named("response", types.A).Description("response object as in the `chainloop discover` CLI output"),
+		),
+		Nondeterministic: true,
+	}, getDiscoverImpl(conn))
+}
+
+func getDiscoverImpl(conn *grpc.ClientConn) topdown.BuiltinFunc {
+	return func(bctx topdown.BuiltinContext, operands []*ast.Term, iter func(*ast.Term) error) error {
+		if len(operands) < 1 {
+			return errors.New("need at least one operand")
+		}
+
+		var digest, kind ast.String
+		var ok bool
+
+		// Extract digest
+		digest, ok = operands[0].Value.(ast.String)
+		if !ok {
+			return errors.New("digest must be a string")
+		}
+
+		if len(operands) > 1 {
+			// Extract kind
+			kind, ok = operands[1].Value.(ast.String)
+			if !ok {
+				return errors.New("kind must be a string")
+			}
+		}
+
+		// Call the service
+		client := v1.NewReferrerServiceClient(conn)
+		resp, err := client.DiscoverPrivate(bctx.Context, &v1.ReferrerServiceDiscoverPrivateRequest{
+			Digest: string(digest), Kind: string(kind),
+		})
+
+		if err != nil {
+			return fmt.Errorf("failed to call discover endpoint: %w", err)
+		}
+
+		// call the iterator with the output value
+		return iter(ast.NewTerm(ast.MustInterfaceToValue(resp.Result)))
+	}
+}