diff --git a/internal/librariangen/bazel/parser.go b/internal/librariangen/bazel/parser.go
new file mode 100644
index 0000000000..a041903e1c
--- /dev/null
+++ b/internal/librariangen/bazel/parser.go
@@ -0,0 +1,126 @@
+// Copyright 2025 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.
+
+package bazel
+
+import (
+	"errors"
+	"fmt"
+	"log/slog"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strconv"
+	"strings"
+	"sync"
+)
+
+// Config holds configuration extracted from a googleapis BUILD.bazel file.
+type Config struct {
+	grpcServiceConfig string
+	restNumericEnums  bool
+	serviceYAML       string
+	transport         string
+	hasGAPIC          bool
+}
+
+// HasGAPIC indicates whether the GAPIC generator should be run.
+func (c *Config) HasGAPIC() bool { return c.hasGAPIC }
+
+// ServiceYAML is the client config file in the API version directory in googleapis.
+func (c *Config) ServiceYAML() string { return c.serviceYAML }
+
+// GRPCServiceConfig is name of the gRPC service config JSON file.
+func (c *Config) GRPCServiceConfig() string { return c.grpcServiceConfig }
+
+// Transport is typically one of "grpc", "rest" or "grpc+rest".
+func (c *Config) Transport() string { return c.transport }
+
+// HasRESTNumericEnums indicates whether the generated client should support numeric enums.
+func (c *Config) HasRESTNumericEnums() bool { return c.restNumericEnums }
+
+// Validate ensures that the configuration is valid.
+func (c *Config) Validate() error {
+	if c.hasGAPIC {
+		if c.serviceYAML == "" {
+			return errors.New("librariangen: serviceYAML is not set")
+		}
+	}
+	return nil
+}
+
+var javaGapicLibraryRE = regexp.MustCompile(`java_gapic_library\((?s:.)*?\)`)
+// Parse reads a BUILD.bazel file from the given directory and extracts the
+// relevant configuration from the java_gapic_library rule.
+func Parse(dir string) (*Config, error) {
+	c := &Config{}
+	fp := filepath.Join(dir, "BUILD.bazel")
+	data, err := os.ReadFile(fp)
+	if err != nil {
+		return nil, fmt.Errorf("librariangen: failed to read BUILD.bazel file %s: %w", fp, err)
+	}
+	content := string(data)
+
+	gapicLibraryBlock := javaGapicLibraryRE.FindString(content)
+	if gapicLibraryBlock != "" {
+		c.hasGAPIC = true
+		c.grpcServiceConfig = findString(gapicLibraryBlock, "grpc_service_config")
+		c.serviceYAML = strings.TrimPrefix(findString(gapicLibraryBlock, "service_yaml"), ":")
+		c.transport = findString(gapicLibraryBlock, "transport")
+		if c.restNumericEnums, err = findBool(gapicLibraryBlock, "rest_numeric_enums"); err != nil {
+			return nil, fmt.Errorf("librariangen: failed to parse BUILD.bazel file %s: %w", fp, err)
+		}
+	}
+	if err := c.Validate(); err != nil {
+		return nil, fmt.Errorf("librariangen: invalid bazel config in %s: %w", dir, err)
+	}
+	slog.Debug("librariangen: bazel config loaded", "conf", c)
+	return c, nil
+}
+
+var reCache = &sync.Map{}
+
+func getRegexp(key, pattern string) *regexp.Regexp {
+	val, ok := reCache.Load(key)
+	if !ok {
+		val = regexp.MustCompile(pattern)
+		reCache.Store(key, val)
+	}
+	return val.(*regexp.Regexp)
+}
+
+func findString(content, name string) string {
+	re := getRegexp("findString_"+name, fmt.Sprintf(`%s\s*=\s*(?:"([^"]+)"|'([^']+)'){1}`, name))
+	match := re.FindStringSubmatch(content)
+	if len(match) > 2 {
+		if match[1] != "" {
+			return match[1] // Double-quoted
+		}
+		return match[2] // Single-quoted
+	}
+	slog.Debug("librariangen: failed to find string attr in BUILD.bazel", "name", name)
+	return ""
+}
+
+func findBool(content, name string) (bool, error) {
+	re := getRegexp("findBool_"+name, fmt.Sprintf(`%s\s*=\s*(\w+)`, name))
+	if match := re.FindStringSubmatch(content); len(match) > 1 {
+		if b, err := strconv.ParseBool(match[1]); err == nil {
+			return b, nil
+		}
+		return false, fmt.Errorf("librariangen: failed to parse bool attr in BUILD.bazel: %q, got: %q", name, match[1])
+	}
+	slog.Debug("librariangen: failed to find bool attr in BUILD.bazel", "name", name)
+	return false, nil
+}
diff --git a/internal/librariangen/bazel/parser_test.go b/internal/librariangen/bazel/parser_test.go
new file mode 100644
index 0000000000..992665d76d
--- /dev/null
+++ b/internal/librariangen/bazel/parser_test.go
@@ -0,0 +1,248 @@
+// Copyright 2025 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.
+
+package bazel
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestParse(t *testing.T) {
+	content := `
+java_grpc_library(
+    name = "asset_java_grpc",
+    srcs = [":asset_proto"],
+    deps = [":asset_java_proto"],
+)
+
+java_gapic_library(
+    name = "asset_java_gapic",
+    srcs = [":asset_proto_with_info"],
+    grpc_service_config = "cloudasset_grpc_service_config.json",
+    rest_numeric_enums = True,
+    service_yaml = "cloudasset_v1.yaml",
+    test_deps = [
+        ":asset_java_grpc",
+        "//google/iam/v1:iam_java_grpc",
+    ],
+    transport = 'grpc+rest',
+    deps = [
+        ":asset_java_proto",
+        "//google/api:api_java_proto",
+        "//google/iam/v1:iam_java_proto",
+    ],
+)
+`
+	tmpDir := t.TempDir()
+	buildPath := filepath.Join(tmpDir, "BUILD.bazel")
+	if err := os.WriteFile(buildPath, []byte(content), 0644); err != nil {
+		t.Fatalf("failed to write test file: %v", err)
+	}
+
+	got, err := Parse(tmpDir)
+	if err != nil {
+		t.Fatalf("Parse() failed: %v", err)
+	}
+
+	t.Run("HasGAPIC", func(t *testing.T) {
+		if !got.HasGAPIC() {
+			t.Error("HasGAPIC() = false; want true")
+		}
+	})
+	t.Run("ServiceYAML", func(t *testing.T) {
+		if want := "cloudasset_v1.yaml"; got.ServiceYAML() != want {
+			t.Errorf("ServiceYAML() = %q; want %q", got.ServiceYAML(), want)
+		}
+	})
+	t.Run("GRPCServiceConfig", func(t *testing.T) {
+		if want := "cloudasset_grpc_service_config.json"; got.GRPCServiceConfig() != want {
+			t.Errorf("GRPCServiceConfig() = %q; want %q", got.GRPCServiceConfig(), want)
+		}
+	})
+	t.Run("Transport", func(t *testing.T) {
+		if want := "grpc+rest"; got.Transport() != want {
+			t.Errorf("Transport() = %q; want %q", got.Transport(), want)
+		}
+	})
+	t.Run("HasRESTNumericEnums", func(t *testing.T) {
+		if !got.HasRESTNumericEnums() {
+			t.Error("HasRESTNumericEnums() = false; want true")
+		}
+	})
+}
+
+func TestParse_serviceConfigIsTarget(t *testing.T) {
+	content := `
+java_grpc_library(
+    name = "asset_java_grpc",
+    srcs = [":asset_proto"],
+    deps = [":asset_java_proto"],
+)
+
+java_gapic_library(
+    name = "asset_java_gapic",
+    srcs = [":asset_proto_with_info"],
+    grpc_service_config = "cloudasset_grpc_service_config.json",
+    rest_numeric_enums = True,
+    service_yaml = ":cloudasset_v1.yaml",
+    test_deps = [
+        ":asset_java_grpc",
+        "//google/iam/v1:iam_java_grpc",
+    ],
+    transport = "grpc+rest",
+    deps = [
+        ":asset_java_proto",
+        "//google/api:api_java_proto",
+        "//google/iam/v1:iam_java_proto",
+    ],
+)
+`
+	tmpDir := t.TempDir()
+	buildPath := filepath.Join(tmpDir, "BUILD.bazel")
+	if err := os.WriteFile(buildPath, []byte(content), 0644); err != nil {
+		t.Fatalf("failed to write test file: %v", err)
+	}
+
+	got, err := Parse(tmpDir)
+	if err != nil {
+		t.Fatalf("Parse() failed: %v", err)
+	}
+
+	if want := "cloudasset_v1.yaml"; got.ServiceYAML() != want {
+		t.Errorf("ServiceYAML() = %q; want %q", got.ServiceYAML(), want)
+	}
+}
+
+func TestConfig_Validate(t *testing.T) {
+	tests := []struct {
+		name    string
+		cfg     *Config
+		wantErr bool
+	}{
+		{
+			name: "valid GAPIC",
+			cfg: &Config{
+				hasGAPIC:          true,
+				serviceYAML:       "b",
+				grpcServiceConfig: "c",
+				transport:         "d",
+			},
+			wantErr: false,
+		},
+		{
+			name:    "valid non-GAPIC",
+			cfg:     &Config{},
+			wantErr: false,
+		},
+		{
+			name:    "gRPC service config and transport are optional",
+			cfg:     &Config{hasGAPIC: true, serviceYAML: "b"},
+			wantErr: false,
+		},
+		{
+			name:    "missing serviceYAML",
+			cfg:     &Config{hasGAPIC: true, grpcServiceConfig: "c", transport: "d"},
+			wantErr: true,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if err := tt.cfg.Validate(); (err != nil) != tt.wantErr {
+				t.Errorf("Config.Validate() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}
+
+func TestParse_noGapic(t *testing.T) {
+	content := `
+java_grpc_library(
+    name = "asset_java_grpc",
+    srcs = [":asset_proto"],
+    deps = [":asset_java_proto"],
+)
+`
+	tmpDir := t.TempDir()
+	buildPath := filepath.Join(tmpDir, "BUILD.bazel")
+	if err := os.WriteFile(buildPath, []byte(content), 0644); err != nil {
+		t.Fatalf("failed to write test file: %v", err)
+	}
+
+	got, err := Parse(tmpDir)
+	if err != nil {
+		t.Fatalf("Parse() failed: %v", err)
+	}
+
+	if got.HasGAPIC() {
+		t.Error("HasGAPIC() = true; want false")
+	}
+}
+
+func TestParse_missingSomeAttrs(t *testing.T) {
+	content := `
+java_gapic_library(
+    name = "asset_java_gapic",
+    service_yaml = "cloudasset_v1.yaml",
+)
+`
+	tmpDir := t.TempDir()
+	buildPath := filepath.Join(tmpDir, "BUILD.bazel")
+	if err := os.WriteFile(buildPath, []byte(content), 0644); err != nil {
+		t.Fatalf("failed to write test file: %v", err)
+	}
+
+	got, err := Parse(tmpDir)
+	if err != nil {
+		t.Fatalf("Parse() failed: %v", err)
+	}
+
+	if got.GRPCServiceConfig() != "" {
+		t.Errorf("GRPCServiceConfig() = %q; want \"\"", got.GRPCServiceConfig())
+	}
+	if got.Transport() != "" {
+		t.Errorf("Transport() = %q; want \"\"", got.Transport())
+	}
+	if got.HasRESTNumericEnums() {
+		t.Error("HasRESTNumericEnums() = true; want false")
+	}
+}
+
+func TestParse_invalidBoolAttr(t *testing.T) {
+	content := `
+java_gapic_library(
+    name = "asset_java_gapic",
+    rest_numeric_enums = "not-a-bool",
+)
+`
+	tmpDir := t.TempDir()
+	buildPath := filepath.Join(tmpDir, "BUILD.bazel")
+	if err := os.WriteFile(buildPath, []byte(content), 0644); err != nil {
+		t.Fatalf("failed to write test file: %v", err)
+	}
+
+	_, err := Parse(tmpDir)
+	if err == nil {
+		t.Error("Parse() succeeded; want error")
+	}
+}
+
+func TestParse_noBuildFile(t *testing.T) {
+	tmpDir := t.TempDir()
+	_, err := Parse(tmpDir)
+	if err == nil {
+		t.Error("Parse() succeeded; want error")
+	}
+}
\ No newline at end of file