diff --git a/proto/dev/cel/expr/conformance/BUILD.bazel b/proto/dev/cel/expr/conformance/BUILD.bazel
new file mode 100644
index 00000000..d54b709b
--- /dev/null
+++ b/proto/dev/cel/expr/conformance/BUILD.bazel
@@ -0,0 +1,51 @@
+package(default_visibility = ["//visibility:public"])
+
+##############################################################################
+# Common
+##############################################################################
+
+proto_library(
+    name = "conformance_proto",
+    srcs = [
+        "conformance_service.proto",
+    ],
+    strip_import_prefix = "/proto",
+    deps = [
+        "//proto/dev/cel/expr:expr_proto",
+        "@com_google_googleapis//google/api:client_proto",
+        "@com_google_googleapis//google/rpc:status_proto",
+    ],
+)
+
+##############################################################################
+# Java
+##############################################################################
+java_proto_library(
+    name = "conformance_java_proto",
+    deps = [":conformance_proto"],
+)
+
+###############################################################################
+## Go
+###############################################################################
+
+load("@io_bazel_rules_go//proto:def.bzl", "go_proto_library")
+
+go_proto_library(
+    name = "conformance_go_proto",
+    importpath = "dev.cel/expr/conformance",
+    protos = [":conformance_proto"],
+    deps = [
+        "//proto/dev/cel/expr:expr_go_proto",
+        "//proto/dev/cel/expr:google_rpc_status_go_proto",
+    ],
+)
+
+###############################################################################
+## C++
+###############################################################################
+
+cc_proto_library(
+    name = "conformance_cc_proto",
+    deps = [":conformance_proto"],
+)
diff --git a/proto/dev/cel/expr/conformance/conformance_service.proto b/proto/dev/cel/expr/conformance/conformance_service.proto
new file mode 100644
index 00000000..149e0674
--- /dev/null
+++ b/proto/dev/cel/expr/conformance/conformance_service.proto
@@ -0,0 +1,180 @@
+// Copyright 2022 Google LLC
+//
+// 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.
+
+syntax = "proto3";
+
+package dev.cel.expr.conformance;
+
+import "dev/cel/expr/checked.proto";
+import "dev/cel/expr/eval.proto";
+import "dev/cel/expr/syntax.proto";
+import "google/rpc/status.proto";
+
+option cc_enable_arenas = true;
+option go_package = "dev.cel/expr/conformance";
+option java_multiple_files = true;
+option java_outer_classname = "ConformanceServiceProto";
+option java_package = "dev.cel.expr";
+
+// Access a CEL implementation from another process or machine.
+// A CEL implementation is decomposed as a parser, a static checker,
+// and an evaluator.  Every CEL implementation is expected to provide
+// a server for this API.  The API will be used for conformance testing
+// and other utilities.
+service ConformanceService {
+  // Transforms CEL source text into a parsed representation.
+  rpc Parse(ParseRequest) returns (ParseResponse) {
+  }
+
+  // Runs static checks on a parsed CEL representation and return
+  // an annotated representation, or a set of issues.
+  rpc Check(CheckRequest) returns (CheckResponse) {
+  }
+
+  // Evaluates a parsed or annotation CEL representation given
+  // values of external bindings.
+  rpc Eval(EvalRequest) returns (EvalResponse) {
+  }
+}
+
+// Request message for the Parse method.
+message ParseRequest {
+  // Required. Source text in CEL syntax.
+  string cel_source = 1;
+
+  // Tag for version of CEL syntax, for future use.
+  string syntax_version = 2;
+
+  // File or resource for source text, used in [SourceInfo][google.api.SourceInfo].
+  string source_location = 3;
+
+  // Prevent macro expansion.  See "Macros" in Language Defiinition.
+  bool disable_macros = 4;
+}
+
+// Response message for the Parse method.
+message ParseResponse {
+  // The parsed representation, or unset if parsing failed.
+  dev.cel.expr.ParsedExpr parsed_expr = 1;
+
+  // Any number of issues with [StatusDetails][] as the details.
+  repeated google.rpc.Status issues = 2;
+}
+
+// Request message for the Check method.
+message CheckRequest {
+  // Required. The parsed representation of the CEL program.
+  dev.cel.expr.ParsedExpr parsed_expr = 1;
+
+  // Declarations of types for external variables and functions.
+  // Required if program uses external variables or functions
+  // not in the default environment.
+  repeated dev.cel.expr.Decl type_env = 2;
+
+  // The protocol buffer context.  See "Name Resolution" in the
+  // Language Definition.
+  string container = 3;
+
+  // If true, use only the declarations in [type_env][google.api.expr.conformance.v1alpha1.CheckRequest.type_env].  If false (default),
+  // add declarations for the standard definitions to the type environment.  See
+  // "Standard Definitions" in the Language Definition.
+  bool no_std_env = 4;
+}
+
+// Response message for the Check method.
+message CheckResponse {
+  // The annotated representation, or unset if checking failed.
+  dev.cel.expr.CheckedExpr checked_expr = 1;
+
+  // Any number of issues with [StatusDetails][] as the details.
+  repeated google.rpc.Status issues = 2;
+}
+
+// Request message for the Eval method.
+message EvalRequest {
+  // Required. Either the parsed or annotated representation of the CEL program.
+  oneof expr_kind {
+    // Evaluate based on the parsed representation.
+    dev.cel.expr.ParsedExpr parsed_expr = 1;
+
+    // Evaluate based on the checked representation.
+    dev.cel.expr.CheckedExpr checked_expr = 2;
+  }
+
+  // Bindings for the external variables.  The types SHOULD be compatible
+  // with the type environment in [CheckRequest][google.api.expr.conformance.v1alpha1.CheckRequest], if checked.
+  map<string, dev.cel.expr.ExprValue> bindings = 3;
+
+  // SHOULD be the same container as used in [CheckRequest][google.api.expr.conformance.v1alpha1.CheckRequest], if checked.
+  string container = 4;
+}
+
+// Response message for the Eval method.
+message EvalResponse {
+  // The execution result, or unset if execution couldn't start.
+  dev.cel.expr.ExprValue result = 1;
+
+  // Any number of issues with [StatusDetails][] as the details.
+  // Note that CEL execution errors are reified into [ExprValue][].
+  // Nevertheless, we'll allow out-of-band issues to be raised,
+  // which also makes the replies more regular.
+  repeated google.rpc.Status issues = 2;
+}
+
+// A specific position in source.
+message SourcePosition {
+  // The source location name (e.g. file name).
+  string location = 1;
+
+  // The UTF-8 code unit offset.
+  int32 offset = 2;
+
+  // The 1-based index of the starting line in the source text
+  // where the issue occurs, or 0 if unknown.
+  int32 line = 3;
+
+  // The 0-based index of the starting position within the line of source text
+  // where the issue occurs.  Only meaningful if line is nonzero.
+  int32 column = 4;
+}
+
+// Warnings or errors in service execution are represented by
+// [google.rpc.Status][google.rpc.Status] messages, with the following message
+// in the details field.
+message IssueDetails {
+  // Severities of issues.
+  enum Severity {
+    // An unspecified severity.
+    SEVERITY_UNSPECIFIED = 0;
+
+    // Deprecation issue for statements and method that may no longer be
+    // supported or maintained.
+    DEPRECATION = 1;
+
+    // Warnings such as: unused variables.
+    WARNING = 2;
+
+    // Errors such as: unmatched curly braces or variable redefinition.
+    ERROR = 3;
+  }
+
+  // The severity of the issue.
+  Severity severity = 1;
+
+  // Position in the source, if known.
+  SourcePosition position = 2;
+
+  // Expression ID from [Expr][], 0 if unknown.
+  int64 id = 3;
+}