diff --git a/api/errors/errors.go b/api/errors/errors.go
index 6f839b8..8b5380e 100644
--- a/api/errors/errors.go
+++ b/api/errors/errors.go
@@ -1,10 +1,12 @@
 package errors
 
 import (
+	"errors"
 	"fmt"
 	"net/http"
 
-	frosterrors "git.frostfs.info/TrueCloudLab/frostfs-s3-gw/internal/frostfs/errors"
+	layerErr "git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer/errors"
+	frostErr "git.frostfs.info/TrueCloudLab/frostfs-s3-gw/internal/frostfs/errors"
 )
 
 type (
@@ -1765,7 +1767,7 @@ var errorCodes = errorCodeMap{
 
 // IsS3Error checks if the provided error is a specific s3 error.
 func IsS3Error(err error, code ErrorCode) bool {
-	err = frosterrors.UnwrapErr(err)
+	err = frostErr.UnwrapErr(err)
 	e, ok := err.(Error)
 	return ok && e.ErrCode == code
 }
@@ -1802,6 +1804,26 @@ func GetAPIErrorWithError(code ErrorCode, err error) Error {
 	return errorCodes.toAPIErrWithErr(code, err)
 }
 
+// TransformToS3Error converts FrostFS error to the corresponding S3 error type.
+func TransformToS3Error(err error) error {
+	err = frostErr.UnwrapErr(err) // this wouldn't work with errors.Join
+	var s3err Error
+	if errors.As(err, &s3err) {
+		return err
+	}
+
+	if errors.Is(err, layerErr.ErrAccessDenied) ||
+		errors.Is(err, layerErr.ErrNodeAccessDenied) {
+		return GetAPIError(ErrAccessDenied)
+	}
+
+	if errors.Is(err, layerErr.ErrGatewayTimeout) {
+		return GetAPIError(ErrGatewayTimeout)
+	}
+
+	return GetAPIError(ErrInternalError)
+}
+
 // ObjectError -- error that is linked to a specific object.
 type ObjectError struct {
 	Err     error
diff --git a/api/handler/util.go b/api/handler/util.go
index dde5274..8fe1f75 100644
--- a/api/handler/util.go
+++ b/api/handler/util.go
@@ -13,7 +13,6 @@ import (
 	s3errors "git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/errors"
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer"
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/middleware"
-	frosterrors "git.frostfs.info/TrueCloudLab/frostfs-s3-gw/internal/frostfs/errors"
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/internal/logs"
 	cid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/container/id"
 	"go.opentelemetry.io/otel/trace"
@@ -30,7 +29,7 @@ func (h *handler) reqLogger(ctx context.Context) *zap.Logger {
 
 func (h *handler) logAndSendError(w http.ResponseWriter, logText string, reqInfo *middleware.ReqInfo, err error, additional ...zap.Field) {
 	err = handleDeleteMarker(w, err)
-	if code, wrErr := middleware.WriteErrorResponse(w, reqInfo, transformToS3Error(err)); wrErr != nil {
+	if code, wrErr := middleware.WriteErrorResponse(w, reqInfo, s3errors.TransformToS3Error(err)); wrErr != nil {
 		additional = append(additional, zap.NamedError("write_response_error", wrErr))
 	} else {
 		additional = append(additional, zap.Int("status", code))
@@ -60,24 +59,6 @@ func handleDeleteMarker(w http.ResponseWriter, err error) error {
 	return fmt.Errorf("%w: %s", s3errors.GetAPIError(target.ErrorCode), err)
 }
 
-func transformToS3Error(err error) error {
-	err = frosterrors.UnwrapErr(err) // this wouldn't work with errors.Join
-	if _, ok := err.(s3errors.Error); ok {
-		return err
-	}
-
-	if errors.Is(err, layer.ErrAccessDenied) ||
-		errors.Is(err, layer.ErrNodeAccessDenied) {
-		return s3errors.GetAPIError(s3errors.ErrAccessDenied)
-	}
-
-	if errors.Is(err, layer.ErrGatewayTimeout) {
-		return s3errors.GetAPIError(s3errors.ErrGatewayTimeout)
-	}
-
-	return s3errors.GetAPIError(s3errors.ErrInternalError)
-}
-
 func (h *handler) ResolveBucket(ctx context.Context, bucket string) (*data.BucketInfo, error) {
 	return h.obj.GetBucketInfo(ctx, bucket)
 }
diff --git a/api/handler/util_test.go b/api/handler/util_test.go
index 587f92c..6c769ca 100644
--- a/api/handler/util_test.go
+++ b/api/handler/util_test.go
@@ -1,12 +1,12 @@
 package handler
 
 import (
-	"errors"
+	stdErrors "errors"
 	"fmt"
 	"testing"
 
 	s3errors "git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/errors"
-	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer"
+	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer/errors"
 	"github.com/stretchr/testify/require"
 )
 
@@ -18,27 +18,27 @@ func TestTransformS3Errors(t *testing.T) {
 	}{
 		{
 			name:     "simple std error to internal error",
-			err:      errors.New("some error"),
+			err:      stdErrors.New("some error"),
 			expected: s3errors.ErrInternalError,
 		},
 		{
 			name:     "layer access denied error to s3 access denied error",
-			err:      layer.ErrAccessDenied,
+			err:      errors.ErrAccessDenied,
 			expected: s3errors.ErrAccessDenied,
 		},
 		{
 			name:     "wrapped layer access denied error to s3 access denied error",
-			err:      fmt.Errorf("wrap: %w", layer.ErrAccessDenied),
+			err:      fmt.Errorf("wrap: %w", errors.ErrAccessDenied),
 			expected: s3errors.ErrAccessDenied,
 		},
 		{
 			name:     "layer node access denied error to s3 access denied error",
-			err:      layer.ErrNodeAccessDenied,
+			err:      errors.ErrNodeAccessDenied,
 			expected: s3errors.ErrAccessDenied,
 		},
 		{
 			name:     "layer gateway timeout error to s3 gateway timeout error",
-			err:      layer.ErrGatewayTimeout,
+			err:      errors.ErrGatewayTimeout,
 			expected: s3errors.ErrGatewayTimeout,
 		},
 		{
@@ -53,7 +53,7 @@ func TestTransformS3Errors(t *testing.T) {
 		},
 	} {
 		t.Run(tc.name, func(t *testing.T) {
-			err := transformToS3Error(tc.err)
+			err := s3errors.TransformToS3Error(tc.err)
 			s3err, ok := err.(s3errors.Error)
 			require.True(t, ok, "error must be s3 error")
 			require.Equalf(t, tc.expected, s3err.ErrCode,
diff --git a/api/layer/compound.go b/api/layer/compound.go
index 7ff3e37..bf0e24d 100644
--- a/api/layer/compound.go
+++ b/api/layer/compound.go
@@ -7,6 +7,7 @@ import (
 
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/data"
 	s3errors "git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/errors"
+	layerErr "git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer/errors"
 )
 
 func (n *Layer) GetObjectTaggingAndLock(ctx context.Context, objVersion *data.ObjectVersion, nodeVersion *data.NodeVersion) (map[string]string, data.LockInfo, error) {
@@ -29,7 +30,7 @@ func (n *Layer) GetObjectTaggingAndLock(ctx context.Context, objVersion *data.Ob
 
 	tags, lockInfo, err = n.treeService.GetObjectTaggingAndLock(ctx, objVersion.BktInfo, nodeVersion)
 	if err != nil {
-		if errors.Is(err, ErrNodeNotFound) {
+		if errors.Is(err, layerErr.ErrNodeNotFound) {
 			return nil, data.LockInfo{}, fmt.Errorf("%w: %s", s3errors.GetAPIError(s3errors.ErrNoSuchKey), err.Error())
 		}
 		return nil, data.LockInfo{}, err
diff --git a/api/layer/cors.go b/api/layer/cors.go
index 43c0491..953b25d 100644
--- a/api/layer/cors.go
+++ b/api/layer/cors.go
@@ -3,12 +3,13 @@ package layer
 import (
 	"bytes"
 	"context"
-	errorsStd "errors"
+	stdErrors "errors"
 	"fmt"
 	"io"
 
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/data"
-	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/errors"
+	apiErrors "git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/errors"
+	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer/errors"
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/internal/logs"
 	cid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/container/id"
 	oid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/id"
@@ -31,7 +32,7 @@ func (n *Layer) PutBucketCORS(ctx context.Context, p *PutCORSParams) error {
 	}
 
 	if cors.CORSRules == nil {
-		return errors.GetAPIError(errors.ErrMalformedXML)
+		return apiErrors.GetAPIError(apiErrors.ErrMalformedXML)
 	}
 
 	if err := checkCORS(cors); err != nil {
@@ -61,7 +62,7 @@ func (n *Layer) PutBucketCORS(ctx context.Context, p *PutCORSParams) error {
 	}
 
 	objsToDelete, err := n.treeService.PutBucketCORS(ctx, p.BktInfo, newAddress(corsBkt.CID, createdObj.ID))
-	objToDeleteNotFound := errorsStd.Is(err, ErrNoNodeToRemove)
+	objToDeleteNotFound := stdErrors.Is(err, errors.ErrNoNodeToRemove)
 	if err != nil && !objToDeleteNotFound {
 		return err
 	}
@@ -104,7 +105,7 @@ func (n *Layer) GetBucketCORS(ctx context.Context, bktInfo *data.BucketInfo) (*d
 
 func (n *Layer) DeleteBucketCORS(ctx context.Context, bktInfo *data.BucketInfo) error {
 	objs, err := n.treeService.DeleteBucketCORS(ctx, bktInfo)
-	objNotFound := errorsStd.Is(err, ErrNoNodeToRemove)
+	objNotFound := stdErrors.Is(err, errors.ErrNoNodeToRemove)
 	if err != nil && !objNotFound {
 		return err
 	}
@@ -124,12 +125,12 @@ func checkCORS(cors *data.CORSConfiguration) error {
 	for _, r := range cors.CORSRules {
 		for _, m := range r.AllowedMethods {
 			if _, ok := supportedMethods[m]; !ok {
-				return errors.GetAPIErrorWithError(errors.ErrCORSUnsupportedMethod, fmt.Errorf("unsupported method is %s", m))
+				return apiErrors.GetAPIErrorWithError(apiErrors.ErrCORSUnsupportedMethod, fmt.Errorf("unsupported method is %s", m))
 			}
 		}
 		for _, h := range r.ExposeHeaders {
 			if h == wildcard {
-				return errors.GetAPIError(errors.ErrCORSWildcardExposeHeaders)
+				return apiErrors.GetAPIError(apiErrors.ErrCORSWildcardExposeHeaders)
 			}
 		}
 	}
diff --git a/api/layer/errors/errors.go b/api/layer/errors/errors.go
new file mode 100644
index 0000000..fffdee7
--- /dev/null
+++ b/api/layer/errors/errors.go
@@ -0,0 +1,16 @@
+package errors
+
+import "errors"
+
+var (
+	// ErrAccessDenied is returned from FrostFS in case of access violation.
+	ErrAccessDenied = errors.New("access denied")
+	// ErrGatewayTimeout is returned from FrostFS in case of timeout, deadline exceeded etc.
+	ErrGatewayTimeout = errors.New("gateway timeout")
+	// ErrNodeNotFound is returned from Tree service in case of not found error.
+	ErrNodeNotFound = errors.New("not found")
+	// ErrNodeAccessDenied is returned from Tree service in case of access denied error.
+	ErrNodeAccessDenied = errors.New("access denied")
+	// ErrNoNodeToRemove is returned from Tree service in case of the lack of node with OID to remove.
+	ErrNoNodeToRemove = errors.New("no node to remove")
+)
diff --git a/api/layer/frostfs.go b/api/layer/frostfs.go
index 3f01f2f..37aa5c5 100644
--- a/api/layer/frostfs.go
+++ b/api/layer/frostfs.go
@@ -3,7 +3,6 @@ package layer
 import (
 	"context"
 	"crypto/ecdsa"
-	"errors"
 	"io"
 	"time"
 
@@ -221,14 +220,6 @@ type PrmObjectPatch struct {
 	ObjectSize uint64
 }
 
-var (
-	// ErrAccessDenied is returned from FrostFS in case of access violation.
-	ErrAccessDenied = errors.New("access denied")
-
-	// ErrGatewayTimeout is returned from FrostFS in case of timeout, deadline exceeded etc.
-	ErrGatewayTimeout = errors.New("gateway timeout")
-)
-
 // FrostFS represents virtual connection to FrostFS network.
 type FrostFS interface {
 	// CreateContainer creates and saves parameterized container in FrostFS.
diff --git a/api/layer/frostfs_mock.go b/api/layer/frostfs_mock.go
index b416dcc..7d3297b 100644
--- a/api/layer/frostfs_mock.go
+++ b/api/layer/frostfs_mock.go
@@ -12,6 +12,7 @@ import (
 
 	v2container "git.frostfs.info/TrueCloudLab/frostfs-api-go/v2/container"
 	objectv2 "git.frostfs.info/TrueCloudLab/frostfs-api-go/v2/object"
+	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer/errors"
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/middleware"
 	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/bearer"
 	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/checksum"
@@ -220,7 +221,7 @@ func (t *TestFrostFS) retrieveObject(ctx context.Context, cnrID cid.ID, objID oi
 	if obj, ok := t.objects[sAddr]; ok {
 		owner := getBearerOwner(ctx)
 		if !t.checkAccess(cnrID, owner) {
-			return nil, ErrAccessDenied
+			return nil, errors.ErrAccessDenied
 		}
 
 		return obj, nil
@@ -345,7 +346,7 @@ func (t *TestFrostFS) DeleteObject(ctx context.Context, prm PrmObjectDelete) err
 	if _, ok := t.objects[addr.EncodeToString()]; ok {
 		owner := getBearerOwner(ctx)
 		if !t.checkAccess(prm.Container, owner) {
-			return ErrAccessDenied
+			return errors.ErrAccessDenied
 		}
 
 		delete(t.objects, addr.EncodeToString())
diff --git a/api/layer/layer.go b/api/layer/layer.go
index 57f804d..c87fe1a 100644
--- a/api/layer/layer.go
+++ b/api/layer/layer.go
@@ -17,9 +17,9 @@ import (
 
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api"
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/data"
-	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/errors"
 	s3errors "git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/errors"
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer/encryption"
+	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer/errors"
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/middleware"
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/internal/logs"
 	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/bearer"
@@ -331,7 +331,7 @@ func (n *Layer) GetBucketInfo(ctx context.Context, name string) (*data.BucketInf
 	containerID, err := n.ResolveBucket(ctx, zone, name)
 	if err != nil {
 		if strings.Contains(err.Error(), "not found") {
-			return nil, fmt.Errorf("%w: %s", errors.GetAPIError(errors.ErrNoSuchBucket), err.Error())
+			return nil, fmt.Errorf("%w: %s", s3errors.GetAPIError(s3errors.ErrNoSuchBucket), err.Error())
 		}
 		return nil, err
 	}
@@ -397,9 +397,9 @@ func (n *Layer) GetObject(ctx context.Context, p *GetObjectParams) (*ObjectPaylo
 	if err != nil {
 		if client.IsErrObjectNotFound(err) {
 			if p.Versioned {
-				err = fmt.Errorf("%w: %s", errors.GetAPIError(errors.ErrNoSuchVersion), err.Error())
+				err = fmt.Errorf("%w: %s", s3errors.GetAPIError(s3errors.ErrNoSuchVersion), err.Error())
 			} else {
-				err = fmt.Errorf("%w: %s", errors.GetAPIError(errors.ErrNoSuchKey), err.Error())
+				err = fmt.Errorf("%w: %s", s3errors.GetAPIError(s3errors.ErrNoSuchKey), err.Error())
 			}
 		}
 
@@ -655,15 +655,15 @@ func (n *Layer) handleNotFoundError(bkt *data.BucketInfo, obj *VersionedObject)
 }
 
 func isNotFoundError(err error) bool {
-	return errors.IsS3Error(err, errors.ErrNoSuchKey) ||
-		errors.IsS3Error(err, errors.ErrNoSuchVersion)
+	return s3errors.IsS3Error(err, s3errors.ErrNoSuchKey) ||
+		s3errors.IsS3Error(err, s3errors.ErrNoSuchVersion)
 }
 
 func (n *Layer) getNodeVersionsToDelete(ctx context.Context, bkt *data.BucketInfo, obj *VersionedObject) ([]*data.NodeVersion, error) {
 	var versionsToDelete []*data.NodeVersion
 	versions, err := n.treeService.GetVersions(ctx, bkt, obj.Name)
 	if err != nil {
-		if stderrors.Is(err, ErrNodeNotFound) {
+		if stderrors.Is(err, errors.ErrNodeNotFound) {
 			return nil, fmt.Errorf("%w: %s", s3errors.GetAPIError(s3errors.ErrNoSuchKey), err.Error())
 		}
 		return nil, err
@@ -785,17 +785,17 @@ func (n *Layer) DeleteObjects(ctx context.Context, p *DeleteObjectParams) []*Ver
 func (n *Layer) CreateBucket(ctx context.Context, p *CreateBucketParams) (*data.BucketInfo, error) {
 	bktInfo, err := n.GetBucketInfo(ctx, p.Name)
 	if err != nil {
-		if errors.IsS3Error(err, errors.ErrNoSuchBucket) {
+		if s3errors.IsS3Error(err, s3errors.ErrNoSuchBucket) {
 			return n.createContainer(ctx, p)
 		}
 		return nil, err
 	}
 
 	if p.SessionContainerCreation != nil && session.IssuedBy(*p.SessionContainerCreation, bktInfo.Owner) {
-		return nil, errors.GetAPIError(errors.ErrBucketAlreadyOwnedByYou)
+		return nil, s3errors.GetAPIError(s3errors.ErrBucketAlreadyOwnedByYou)
 	}
 
-	return nil, errors.GetAPIError(errors.ErrBucketAlreadyExists)
+	return nil, s3errors.GetAPIError(s3errors.ErrBucketAlreadyExists)
 }
 
 func (n *Layer) ResolveBucket(ctx context.Context, zone, name string) (cid.ID, error) {
@@ -822,7 +822,7 @@ func (n *Layer) DeleteBucket(ctx context.Context, p *DeleteBucketParams) error {
 			return err
 		}
 		if len(res) != 0 {
-			return errors.GetAPIError(errors.ErrBucketNotEmpty)
+			return s3errors.GetAPIError(s3errors.ErrBucketNotEmpty)
 		}
 	}
 
diff --git a/api/layer/lifecycle.go b/api/layer/lifecycle.go
index ad052aa..0610d04 100644
--- a/api/layer/lifecycle.go
+++ b/api/layer/lifecycle.go
@@ -5,12 +5,13 @@ import (
 	"context"
 	"encoding/base64"
 	"encoding/xml"
-	"errors"
+	stderrors "errors"
 	"fmt"
 	"io"
 
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/data"
 	apiErr "git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/errors"
+	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer/errors"
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/internal/logs"
 	oid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/id"
 	"go.uber.org/zap"
@@ -59,7 +60,7 @@ func (n *Layer) PutBucketLifecycleConfiguration(ctx context.Context, p *PutBucke
 	}
 
 	objsToDelete, err := n.treeService.PutBucketLifecycleConfiguration(ctx, p.BktInfo, newAddress(lifecycleBkt.CID, createdObj.ID))
-	objsToDeleteNotFound := errors.Is(err, ErrNoNodeToRemove)
+	objsToDeleteNotFound := stderrors.Is(err, errors.ErrNoNodeToRemove)
 	if err != nil && !objsToDeleteNotFound {
 		return err
 	}
@@ -98,7 +99,7 @@ func (n *Layer) GetBucketLifecycleConfiguration(ctx context.Context, bktInfo *da
 	}
 
 	addr, err := n.treeService.GetBucketLifecycleConfiguration(ctx, bktInfo)
-	objNotFound := errors.Is(err, ErrNodeNotFound)
+	objNotFound := stderrors.Is(err, errors.ErrNodeNotFound)
 	if err != nil && !objNotFound {
 		return nil, err
 	}
@@ -132,7 +133,7 @@ func (n *Layer) GetBucketLifecycleConfiguration(ctx context.Context, bktInfo *da
 
 func (n *Layer) DeleteBucketLifecycleConfiguration(ctx context.Context, bktInfo *data.BucketInfo) error {
 	objs, err := n.treeService.DeleteBucketLifecycleConfiguration(ctx, bktInfo)
-	objsNotFound := errors.Is(err, ErrNoNodeToRemove)
+	objsNotFound := stderrors.Is(err, errors.ErrNoNodeToRemove)
 	if err != nil && !objsNotFound {
 		return err
 	}
diff --git a/api/layer/multipart_upload.go b/api/layer/multipart_upload.go
index c99173d..20d8cc1 100644
--- a/api/layer/multipart_upload.go
+++ b/api/layer/multipart_upload.go
@@ -7,7 +7,7 @@ import (
 	"encoding/base64"
 	"encoding/hex"
 	"encoding/json"
-	"errors"
+	stdErrors "errors"
 	"fmt"
 	"io"
 	"sort"
@@ -19,6 +19,7 @@ import (
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/data"
 	s3errors "git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/errors"
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer/encryption"
+	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer/errors"
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/internal/logs"
 	oid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/id"
 	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/user"
@@ -187,7 +188,7 @@ func (n *Layer) CreateMultipartUpload(ctx context.Context, p *CreateMultipartPar
 func (n *Layer) UploadPart(ctx context.Context, p *UploadPartParams) (string, error) {
 	multipartInfo, err := n.treeService.GetMultipartUpload(ctx, p.Info.Bkt, p.Info.Key, p.Info.UploadID)
 	if err != nil {
-		if errors.Is(err, ErrNodeNotFound) {
+		if stdErrors.Is(err, errors.ErrNodeNotFound) {
 			return "", fmt.Errorf("%w: %s", s3errors.GetAPIError(s3errors.ErrNoSuchUpload), err.Error())
 		}
 		return "", err
@@ -291,7 +292,7 @@ func (n *Layer) uploadPart(ctx context.Context, multipartInfo *data.MultipartInf
 	}
 
 	oldPartIDs, err := n.treeService.AddPart(ctx, bktInfo, multipartInfo.ID, partInfo)
-	oldPartIDNotFound := errors.Is(err, ErrNoNodeToRemove)
+	oldPartIDNotFound := stdErrors.Is(err, errors.ErrNoNodeToRemove)
 	if err != nil && !oldPartIDNotFound {
 		return nil, err
 	}
@@ -323,7 +324,7 @@ func (n *Layer) uploadPart(ctx context.Context, multipartInfo *data.MultipartInf
 func (n *Layer) UploadPartCopy(ctx context.Context, p *UploadCopyParams) (*data.ObjectInfo, error) {
 	multipartInfo, err := n.treeService.GetMultipartUpload(ctx, p.Info.Bkt, p.Info.Key, p.Info.UploadID)
 	if err != nil {
-		if errors.Is(err, ErrNodeNotFound) {
+		if stdErrors.Is(err, errors.ErrNodeNotFound) {
 			return nil, fmt.Errorf("%w: %s", s3errors.GetAPIError(s3errors.ErrNoSuchUpload), err.Error())
 		}
 		return nil, err
@@ -646,7 +647,7 @@ func (p PartsInfo) Extract(part int, etag string, md5Enabled bool) *data.PartInf
 func (n *Layer) getUploadParts(ctx context.Context, p *UploadInfoParams) (*data.MultipartInfo, PartsInfo, error) {
 	multipartInfo, err := n.treeService.GetMultipartUpload(ctx, p.Bkt, p.Key, p.UploadID)
 	if err != nil {
-		if errors.Is(err, ErrNodeNotFound) {
+		if stdErrors.Is(err, errors.ErrNodeNotFound) {
 			return nil, nil, fmt.Errorf("%w: %s", s3errors.GetAPIError(s3errors.ErrNoSuchUpload), err.Error())
 		}
 		return nil, nil, err
diff --git a/api/layer/object.go b/api/layer/object.go
index 8c4549d..a4ab324 100644
--- a/api/layer/object.go
+++ b/api/layer/object.go
@@ -8,7 +8,7 @@ import (
 	"encoding/base64"
 	"encoding/hex"
 	"encoding/json"
-	"errors"
+	stdErrors "errors"
 	"fmt"
 	"io"
 	"mime"
@@ -20,6 +20,7 @@ import (
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/auth"
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/data"
 	apiErrors "git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/errors"
+	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer/errors"
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/internal/logs"
 	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/client"
 	cid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/container/id"
@@ -380,7 +381,7 @@ func (n *Layer) headLastVersionIfNotDeleted(ctx context.Context, bkt *data.Bucke
 
 	node, err := n.treeService.GetLatestVersion(ctx, bkt, objectName)
 	if err != nil {
-		if errors.Is(err, ErrNodeNotFound) {
+		if stdErrors.Is(err, errors.ErrNodeNotFound) {
 			return nil, fmt.Errorf("%w: %s", apiErrors.GetAPIError(apiErrors.ErrNoSuchKey), err.Error())
 		}
 		return nil, err
@@ -416,7 +417,7 @@ func (n *Layer) headVersion(ctx context.Context, bkt *data.BucketInfo, p *HeadOb
 	if p.VersionID == data.UnversionedObjectVersionID {
 		foundVersion, err = n.treeService.GetUnversioned(ctx, bkt, p.Object)
 		if err != nil {
-			if errors.Is(err, ErrNodeNotFound) {
+			if stdErrors.Is(err, errors.ErrNodeNotFound) {
 				return nil, fmt.Errorf("%w: %s", apiErrors.GetAPIError(apiErrors.ErrNoSuchVersion), err.Error())
 			}
 			return nil, err
diff --git a/api/layer/system_object.go b/api/layer/system_object.go
index 81f0b3f..46da7c0 100644
--- a/api/layer/system_object.go
+++ b/api/layer/system_object.go
@@ -3,7 +3,7 @@ package layer
 import (
 	"context"
 	"encoding/xml"
-	errorsStd "errors"
+	stdErrors "errors"
 	"fmt"
 	"math"
 	"strconv"
@@ -11,7 +11,8 @@ import (
 
 	"git.frostfs.info/TrueCloudLab/frostfs-api-go/v2/object"
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/data"
-	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/errors"
+	apiErrors "git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/errors"
+	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer/errors"
 	cid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/container/id"
 	oid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/id"
 )
@@ -40,7 +41,7 @@ func (n *Layer) PutLockInfo(ctx context.Context, p *PutLockInfoParams) (err erro
 	}
 
 	lockInfo, err := n.treeService.GetLock(ctx, p.ObjVersion.BktInfo, versionNode.ID)
-	if err != nil && !errorsStd.Is(err, ErrNodeNotFound) {
+	if err != nil && !stdErrors.Is(err, errors.ErrNodeNotFound) {
 		return err
 	}
 
@@ -146,7 +147,7 @@ func (n *Layer) GetLockInfo(ctx context.Context, objVersion *data.ObjectVersion)
 	}
 
 	lockInfo, err := n.treeService.GetLock(ctx, objVersion.BktInfo, versionNode.ID)
-	if err != nil && !errorsStd.Is(err, ErrNodeNotFound) {
+	if err != nil && !stdErrors.Is(err, errors.ErrNodeNotFound) {
 		return nil, err
 	}
 	if lockInfo == nil {
@@ -165,13 +166,13 @@ func (n *Layer) getCORS(ctx context.Context, bkt *data.BucketInfo) (*data.CORSCo
 	}
 
 	addr, err := n.treeService.GetBucketCORS(ctx, bkt)
-	objNotFound := errorsStd.Is(err, ErrNodeNotFound)
+	objNotFound := stdErrors.Is(err, errors.ErrNodeNotFound)
 	if err != nil && !objNotFound {
 		return nil, err
 	}
 
 	if objNotFound {
-		return nil, fmt.Errorf("%w: %s", errors.GetAPIError(errors.ErrNoSuchCORSConfiguration), err.Error())
+		return nil, fmt.Errorf("%w: %s", apiErrors.GetAPIError(apiErrors.ErrNoSuchCORSConfiguration), err.Error())
 	}
 
 	var prmAuth PrmAuth
@@ -209,7 +210,7 @@ func (n *Layer) GetBucketSettings(ctx context.Context, bktInfo *data.BucketInfo)
 
 	settings, err := n.treeService.GetSettingsNode(ctx, bktInfo)
 	if err != nil {
-		if !errorsStd.Is(err, ErrNodeNotFound) {
+		if !stdErrors.Is(err, errors.ErrNodeNotFound) {
 			return nil, err
 		}
 		settings = &data.BucketSettings{Versioning: data.VersioningUnversioned}
diff --git a/api/layer/tagging.go b/api/layer/tagging.go
index 293b6f6..9b6d19a 100644
--- a/api/layer/tagging.go
+++ b/api/layer/tagging.go
@@ -2,11 +2,12 @@ package layer
 
 import (
 	"context"
-	"errors"
+	stdErrors "errors"
 	"fmt"
 
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/data"
 	s3errors "git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/errors"
+	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer/errors"
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/internal/logs"
 	cid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/container/id"
 	oid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/id"
@@ -39,7 +40,7 @@ func (n *Layer) GetObjectTagging(ctx context.Context, p *data.GetObjectTaggingPa
 
 	tags, err := n.treeService.GetObjectTagging(ctx, p.ObjectVersion.BktInfo, nodeVersion)
 	if err != nil {
-		if errors.Is(err, ErrNodeNotFound) {
+		if stdErrors.Is(err, errors.ErrNodeNotFound) {
 			return "", nil, fmt.Errorf("%w: %s", s3errors.GetAPIError(s3errors.ErrNoSuchKey), err.Error())
 		}
 		return "", nil, err
@@ -62,7 +63,7 @@ func (n *Layer) PutObjectTagging(ctx context.Context, p *data.PutObjectTaggingPa
 
 	err = n.treeService.PutObjectTagging(ctx, p.ObjectVersion.BktInfo, nodeVersion, p.TagSet)
 	if err != nil {
-		if errors.Is(err, ErrNodeNotFound) {
+		if stdErrors.Is(err, errors.ErrNodeNotFound) {
 			return fmt.Errorf("%w: %s", s3errors.GetAPIError(s3errors.ErrNoSuchKey), err.Error())
 		}
 		return err
@@ -81,7 +82,7 @@ func (n *Layer) DeleteObjectTagging(ctx context.Context, p *data.ObjectVersion)
 
 	err = n.treeService.DeleteObjectTagging(ctx, p.BktInfo, version)
 	if err != nil {
-		if errors.Is(err, ErrNodeNotFound) {
+		if stdErrors.Is(err, errors.ErrNodeNotFound) {
 			return fmt.Errorf("%w: %s", s3errors.GetAPIError(s3errors.ErrNoSuchKey), err.Error())
 		}
 		return err
@@ -102,7 +103,7 @@ func (n *Layer) GetBucketTagging(ctx context.Context, bktInfo *data.BucketInfo)
 	}
 
 	tags, err := n.treeService.GetBucketTagging(ctx, bktInfo)
-	if err != nil && !errors.Is(err, ErrNodeNotFound) {
+	if err != nil && !stdErrors.Is(err, errors.ErrNodeNotFound) {
 		return nil, err
 	}
 
@@ -161,7 +162,7 @@ func (n *Layer) getNodeVersion(ctx context.Context, objVersion *data.ObjectVersi
 
 	if err == nil && version.IsDeleteMarker && !objVersion.NoErrorOnDeleteMarker {
 		return nil, fmt.Errorf("%w: found version is delete marker", s3errors.GetAPIError(s3errors.ErrNoSuchKey))
-	} else if errors.Is(err, ErrNodeNotFound) {
+	} else if stdErrors.Is(err, errors.ErrNodeNotFound) {
 		return nil, fmt.Errorf("%w: %s", s3errors.GetAPIError(s3errors.ErrNoSuchKey), err.Error())
 	}
 
diff --git a/api/layer/tree_mock.go b/api/layer/tree_mock.go
index 8a85ffb..738b243 100644
--- a/api/layer/tree_mock.go
+++ b/api/layer/tree_mock.go
@@ -9,6 +9,7 @@ import (
 	"time"
 
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/data"
+	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer/errors"
 	oid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/id"
 )
 
@@ -105,7 +106,7 @@ func (t *TreeServiceMock) PutSettingsNode(_ context.Context, bktInfo *data.Bucke
 func (t *TreeServiceMock) GetSettingsNode(_ context.Context, bktInfo *data.BucketInfo) (*data.BucketSettings, error) {
 	settings, ok := t.settings[bktInfo.CID.EncodeToString()]
 	if !ok {
-		return nil, ErrNodeNotFound
+		return nil, errors.ErrNodeNotFound
 	}
 
 	return settings, nil
@@ -140,7 +141,7 @@ func (t *TreeServiceMock) PutBucketCORS(_ context.Context, bktInfo *data.BucketI
 
 	t.system[bktInfo.CID.EncodeToString()] = systemMap
 
-	return nil, ErrNoNodeToRemove
+	return nil, errors.ErrNoNodeToRemove
 }
 
 func (t *TreeServiceMock) DeleteBucketCORS(context.Context, *data.BucketInfo) ([]oid.Address, error) {
@@ -150,12 +151,12 @@ func (t *TreeServiceMock) DeleteBucketCORS(context.Context, *data.BucketInfo) ([
 func (t *TreeServiceMock) GetVersions(_ context.Context, bktInfo *data.BucketInfo, objectName string) ([]*data.NodeVersion, error) {
 	cnrVersionsMap, ok := t.versions[bktInfo.CID.EncodeToString()]
 	if !ok {
-		return nil, ErrNodeNotFound
+		return nil, errors.ErrNodeNotFound
 	}
 
 	versions, ok := cnrVersionsMap[objectName]
 	if !ok {
-		return nil, ErrNodeNotFound
+		return nil, errors.ErrNodeNotFound
 	}
 
 	return versions, nil
@@ -164,12 +165,12 @@ func (t *TreeServiceMock) GetVersions(_ context.Context, bktInfo *data.BucketInf
 func (t *TreeServiceMock) GetLatestVersion(_ context.Context, bktInfo *data.BucketInfo, objectName string) (*data.NodeVersion, error) {
 	cnrVersionsMap, ok := t.versions[bktInfo.CID.EncodeToString()]
 	if !ok {
-		return nil, ErrNodeNotFound
+		return nil, errors.ErrNodeNotFound
 	}
 
 	versions, ok := cnrVersionsMap[objectName]
 	if !ok {
-		return nil, ErrNodeNotFound
+		return nil, errors.ErrNodeNotFound
 	}
 
 	sort.Slice(versions, func(i, j int) bool {
@@ -180,13 +181,13 @@ func (t *TreeServiceMock) GetLatestVersion(_ context.Context, bktInfo *data.Buck
 		return versions[len(versions)-1], nil
 	}
 
-	return nil, ErrNodeNotFound
+	return nil, errors.ErrNodeNotFound
 }
 
 func (t *TreeServiceMock) InitVersionsByPrefixStream(_ context.Context, bktInfo *data.BucketInfo, prefix string, latestOnly bool) (data.VersionsStream, error) {
 	cnrVersionsMap, ok := t.versions[bktInfo.CID.EncodeToString()]
 	if !ok {
-		return nil, ErrNodeNotFound
+		return nil, errors.ErrNodeNotFound
 	}
 
 	var result []*data.NodeVersion
@@ -218,12 +219,12 @@ func (t *TreeServiceMock) InitVersionsByPrefixStream(_ context.Context, bktInfo
 func (t *TreeServiceMock) GetUnversioned(_ context.Context, bktInfo *data.BucketInfo, objectName string) (*data.NodeVersion, error) {
 	cnrVersionsMap, ok := t.versions[bktInfo.CID.EncodeToString()]
 	if !ok {
-		return nil, ErrNodeNotFound
+		return nil, errors.ErrNodeNotFound
 	}
 
 	versions, ok := cnrVersionsMap[objectName]
 	if !ok {
-		return nil, ErrNodeNotFound
+		return nil, errors.ErrNodeNotFound
 	}
 
 	for _, version := range versions {
@@ -232,7 +233,7 @@ func (t *TreeServiceMock) GetUnversioned(_ context.Context, bktInfo *data.Bucket
 		}
 	}
 
-	return nil, ErrNodeNotFound
+	return nil, errors.ErrNodeNotFound
 }
 
 func (t *TreeServiceMock) AddVersion(_ context.Context, bktInfo *data.BucketInfo, newVersion *data.NodeVersion) (uint64, error) {
@@ -278,7 +279,7 @@ func (t *TreeServiceMock) AddVersion(_ context.Context, bktInfo *data.BucketInfo
 func (t *TreeServiceMock) RemoveVersion(_ context.Context, bktInfo *data.BucketInfo, nodeID uint64) error {
 	cnrVersionsMap, ok := t.versions[bktInfo.CID.EncodeToString()]
 	if !ok {
-		return ErrNodeNotFound
+		return errors.ErrNodeNotFound
 	}
 
 	for key, versions := range cnrVersionsMap {
@@ -290,7 +291,7 @@ func (t *TreeServiceMock) RemoveVersion(_ context.Context, bktInfo *data.BucketI
 		}
 	}
 
-	return ErrNodeNotFound
+	return errors.ErrNodeNotFound
 }
 
 func (t *TreeServiceMock) GetAllVersionsByPrefix(_ context.Context, bktInfo *data.BucketInfo, prefix string) ([]*data.NodeVersion, error) {
@@ -334,7 +335,7 @@ func (t *TreeServiceMock) GetMultipartUploadsByPrefix(context.Context, *data.Buc
 func (t *TreeServiceMock) GetMultipartUpload(_ context.Context, bktInfo *data.BucketInfo, objectName, uploadID string) (*data.MultipartInfo, error) {
 	cnrMultipartsMap, ok := t.multiparts[bktInfo.CID.EncodeToString()]
 	if !ok {
-		return nil, ErrNodeNotFound
+		return nil, errors.ErrNodeNotFound
 	}
 
 	multiparts := cnrMultipartsMap[objectName]
@@ -344,7 +345,7 @@ func (t *TreeServiceMock) GetMultipartUpload(_ context.Context, bktInfo *data.Bu
 		}
 	}
 
-	return nil, ErrNodeNotFound
+	return nil, errors.ErrNodeNotFound
 }
 
 func (t *TreeServiceMock) AddPart(ctx context.Context, bktInfo *data.BucketInfo, multipartNodeID uint64, info *data.PartInfo) (oldObjIDsToDelete []oid.ID, err error) {
@@ -387,7 +388,7 @@ LOOP:
 	}
 
 	if foundMultipart == nil {
-		return nil, ErrNodeNotFound
+		return nil, errors.ErrNodeNotFound
 	}
 
 	partsMap := t.parts[foundMultipart.UploadID]
@@ -411,18 +412,18 @@ func (t *TreeServiceMock) PutBucketLifecycleConfiguration(_ context.Context, bkt
 
 	t.system[bktInfo.CID.EncodeToString()] = systemMap
 
-	return nil, ErrNoNodeToRemove
+	return nil, errors.ErrNoNodeToRemove
 }
 
 func (t *TreeServiceMock) GetBucketLifecycleConfiguration(_ context.Context, bktInfo *data.BucketInfo) (oid.Address, error) {
 	systemMap, ok := t.system[bktInfo.CID.EncodeToString()]
 	if !ok {
-		return oid.Address{}, ErrNodeNotFound
+		return oid.Address{}, errors.ErrNodeNotFound
 	}
 
 	node, ok := systemMap["lifecycle"]
 	if !ok {
-		return oid.Address{}, ErrNodeNotFound
+		return oid.Address{}, errors.ErrNodeNotFound
 	}
 
 	return newAddress(bktInfo.CID, node.OID), nil
@@ -431,12 +432,12 @@ func (t *TreeServiceMock) GetBucketLifecycleConfiguration(_ context.Context, bkt
 func (t *TreeServiceMock) DeleteBucketLifecycleConfiguration(_ context.Context, bktInfo *data.BucketInfo) ([]oid.Address, error) {
 	systemMap, ok := t.system[bktInfo.CID.EncodeToString()]
 	if !ok {
-		return nil, ErrNoNodeToRemove
+		return nil, errors.ErrNoNodeToRemove
 	}
 
 	node, ok := systemMap["lifecycle"]
 	if !ok {
-		return nil, ErrNoNodeToRemove
+		return nil, errors.ErrNoNodeToRemove
 	}
 
 	delete(systemMap, "lifecycle")
@@ -461,7 +462,7 @@ LOOP:
 	}
 
 	if uploadID == "" {
-		return ErrNodeNotFound
+		return errors.ErrNodeNotFound
 	}
 
 	delete(t.parts, uploadID)
diff --git a/api/layer/tree_service.go b/api/layer/tree_service.go
index 5a2047a..ed8dad7 100644
--- a/api/layer/tree_service.go
+++ b/api/layer/tree_service.go
@@ -2,7 +2,6 @@ package layer
 
 import (
 	"context"
-	"errors"
 
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/data"
 	oid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/id"
@@ -72,14 +71,3 @@ type TreeService interface {
 	// GetObjectTaggingAndLock unifies GetObjectTagging and GetLock methods in single tree service invocation.
 	GetObjectTaggingAndLock(ctx context.Context, bktInfo *data.BucketInfo, objVersion *data.NodeVersion) (map[string]string, *data.LockInfo, error)
 }
-
-var (
-	// ErrNodeNotFound is returned from Tree service in case of not found error.
-	ErrNodeNotFound = errors.New("not found")
-
-	// ErrNodeAccessDenied is returned from Tree service in case of access denied error.
-	ErrNodeAccessDenied = errors.New("access denied")
-
-	// ErrNoNodeToRemove is returned from Tree service in case of the lack of node with OID to remove.
-	ErrNoNodeToRemove = errors.New("no node to remove")
-)
diff --git a/api/layer/util.go b/api/layer/util.go
index f3ba2b0..36e81c1 100644
--- a/api/layer/util.go
+++ b/api/layer/util.go
@@ -3,9 +3,7 @@ package layer
 import (
 	"encoding/hex"
 	"fmt"
-	"os"
 	"strconv"
-	"strings"
 	"time"
 
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/data"
@@ -13,9 +11,6 @@ import (
 	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object"
 )
 
-// PathSeparator is a path components separator string.
-const PathSeparator = string(os.PathSeparator)
-
 func userHeaders(attrs []object.Attribute) map[string]string {
 	result := make(map[string]string, len(attrs))
 
@@ -111,9 +106,3 @@ func filepathFromObject(o *object.Object) string {
 	objID, _ := o.ID()
 	return objID.EncodeToString()
 }
-
-// NameFromString splits name into a base file name and a directory path.
-func NameFromString(name string) (string, string) {
-	ind := strings.LastIndex(name, PathSeparator)
-	return name[ind+1:], name[:ind+1]
-}
diff --git a/api/middleware/policy.go b/api/middleware/policy.go
index f3bcd63..4cc8d7f 100644
--- a/api/middleware/policy.go
+++ b/api/middleware/policy.go
@@ -12,7 +12,6 @@ import (
 
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/data"
 	apiErr "git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/errors"
-	frostfsErrors "git.frostfs.info/TrueCloudLab/frostfs-s3-gw/internal/frostfs/errors"
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/internal/logs"
 	"git.frostfs.info/TrueCloudLab/policy-engine/pkg/chain"
 	"git.frostfs.info/TrueCloudLab/policy-engine/pkg/engine"
@@ -85,7 +84,7 @@ func PolicyCheck(cfg PolicyConfig) Func {
 			ctx := r.Context()
 			if err := policyCheck(r, cfg); err != nil {
 				reqLogOrDefault(ctx, cfg.Log).Error(logs.PolicyValidationFailed, zap.Error(err))
-				err = frostfsErrors.UnwrapErr(err)
+				err = apiErr.TransformToS3Error(err)
 				if _, wrErr := WriteErrorResponse(w, GetReqInfo(ctx), err); wrErr != nil {
 					reqLogOrDefault(ctx, cfg.Log).Error(logs.FailedToWriteResponse, zap.Error(wrErr))
 				}
diff --git a/api/middleware/response.go b/api/middleware/response.go
index b94b403..94b633d 100644
--- a/api/middleware/response.go
+++ b/api/middleware/response.go
@@ -62,7 +62,7 @@ const (
 	hdrSSE = "X-Amz-Server-Side-Encryption"
 
 	// hdrSSECustomerKey is the HTTP header key referencing the
-	// SSE-C client-provided key..
+	// SSE-C client-provided key.
 	hdrSSECustomerKey = hdrSSE + "-Customer-Key"
 
 	// hdrSSECopyKey is the HTTP header key referencing the SSE-C
@@ -74,7 +74,7 @@ var (
 	xmlHeader = []byte(xml.Header)
 )
 
-// Non exhaustive list of AWS S3 standard error responses -
+// Non-exhaustive list of AWS S3 standard error responses -
 // http://docs.aws.amazon.com/AmazonS3/latest/API/ErrorResponses.html
 var s3ErrorResponseMap = map[string]string{
 	"AccessDenied":                      "Access Denied.",
diff --git a/internal/frostfs/frostfs.go b/internal/frostfs/frostfs.go
index 5fd935b..85788f1 100644
--- a/internal/frostfs/frostfs.go
+++ b/internal/frostfs/frostfs.go
@@ -11,6 +11,7 @@ import (
 
 	objectv2 "git.frostfs.info/TrueCloudLab/frostfs-api-go/v2/object"
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer"
+	layerErr "git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer/errors"
 	errorsFrost "git.frostfs.info/TrueCloudLab/frostfs-s3-gw/internal/frostfs/errors"
 	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/client"
 	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/container"
@@ -467,11 +468,11 @@ func handleObjectError(msg string, err error) error {
 	}
 
 	if reason, ok := errorsFrost.IsErrObjectAccessDenied(err); ok {
-		return fmt.Errorf("%s: %w: %s", msg, layer.ErrAccessDenied, reason)
+		return fmt.Errorf("%s: %w: %s", msg, layerErr.ErrAccessDenied, reason)
 	}
 
 	if errorsFrost.IsTimeoutError(err) {
-		return fmt.Errorf("%s: %w: %s", msg, layer.ErrGatewayTimeout, err.Error())
+		return fmt.Errorf("%s: %w: %s", msg, layerErr.ErrGatewayTimeout, err.Error())
 	}
 
 	return fmt.Errorf("%s: %w", msg, err)
diff --git a/internal/frostfs/frostfs_test.go b/internal/frostfs/frostfs_test.go
index a3b9bf2..d52072e 100644
--- a/internal/frostfs/frostfs_test.go
+++ b/internal/frostfs/frostfs_test.go
@@ -7,7 +7,7 @@ import (
 	"testing"
 	"time"
 
-	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer"
+	layerErr "git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer/errors"
 	errorsFrost "git.frostfs.info/TrueCloudLab/frostfs-s3-gw/internal/frostfs/errors"
 	apistatus "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/client/status"
 	"github.com/stretchr/testify/require"
@@ -23,10 +23,10 @@ func TestErrorChecking(t *testing.T) {
 	var wrappedError error
 
 	if fetchedReason, ok := errorsFrost.IsErrObjectAccessDenied(err); ok {
-		wrappedError = fmt.Errorf("%w: %s", layer.ErrAccessDenied, fetchedReason)
+		wrappedError = fmt.Errorf("%w: %s", layerErr.ErrAccessDenied, fetchedReason)
 	}
 
-	require.ErrorIs(t, wrappedError, layer.ErrAccessDenied)
+	require.ErrorIs(t, wrappedError, layerErr.ErrAccessDenied)
 	require.Contains(t, wrappedError.Error(), reason)
 }
 
diff --git a/pkg/service/tree/tree.go b/pkg/service/tree/tree.go
index c89d6af..ebd3fa6 100644
--- a/pkg/service/tree/tree.go
+++ b/pkg/service/tree/tree.go
@@ -12,7 +12,7 @@ import (
 	"time"
 
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/data"
-	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer"
+	layerErr "git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer/errors"
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/middleware"
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/internal/logs"
 	cid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/container/id"
@@ -75,13 +75,13 @@ const (
 
 var (
 	// ErrNodeNotFound is returned from ServiceClient in case of not found error.
-	ErrNodeNotFound = layer.ErrNodeNotFound
+	ErrNodeNotFound = layerErr.ErrNodeNotFound
 
 	// ErrNodeAccessDenied is returned from ServiceClient service in case of access denied error.
-	ErrNodeAccessDenied = layer.ErrNodeAccessDenied
+	ErrNodeAccessDenied = layerErr.ErrNodeAccessDenied
 
 	// ErrGatewayTimeout is returned from ServiceClient service in case of timeout error.
-	ErrGatewayTimeout = layer.ErrGatewayTimeout
+	ErrGatewayTimeout = layerErr.ErrGatewayTimeout
 
 	errNodeDoesntContainFileName = fmt.Errorf("node doesn't contain FileName")
 )
@@ -523,7 +523,7 @@ func (c *Tree) GetSettingsNode(ctx context.Context, bktInfo *data.BucketInfo) (*
 
 func (c *Tree) PutSettingsNode(ctx context.Context, bktInfo *data.BucketInfo, settings *data.BucketSettings) error {
 	multiNode, err := c.getSystemNode(ctx, bktInfo, settingsFileName)
-	isErrNotFound := errors.Is(err, layer.ErrNodeNotFound)
+	isErrNotFound := errors.Is(err, layerErr.ErrNodeNotFound)
 	if err != nil && !isErrNotFound {
 		return fmt.Errorf("couldn't get node: %w", err)
 	}
@@ -561,7 +561,7 @@ func (c *Tree) GetBucketCORS(ctx context.Context, bktInfo *data.BucketInfo) (oid
 
 func (c *Tree) PutBucketCORS(ctx context.Context, bktInfo *data.BucketInfo, addr oid.Address) ([]oid.Address, error) {
 	multiNode, err := c.getSystemNode(ctx, bktInfo, corsFilename)
-	isErrNotFound := errors.Is(err, layer.ErrNodeNotFound)
+	isErrNotFound := errors.Is(err, layerErr.ErrNodeNotFound)
 	if err != nil && !isErrNotFound {
 		return nil, fmt.Errorf("couldn't get node: %w", err)
 	}
@@ -575,7 +575,7 @@ func (c *Tree) PutBucketCORS(ctx context.Context, bktInfo *data.BucketInfo, addr
 		if _, err = c.service.AddNode(ctx, bktInfo, systemTree, 0, meta); err != nil {
 			return nil, err
 		}
-		return nil, layer.ErrNoNodeToRemove
+		return nil, layerErr.ErrNoNodeToRemove
 	}
 
 	latest := multiNode.Latest()
@@ -601,13 +601,13 @@ func (c *Tree) PutBucketCORS(ctx context.Context, bktInfo *data.BucketInfo, addr
 
 func (c *Tree) DeleteBucketCORS(ctx context.Context, bktInfo *data.BucketInfo) ([]oid.Address, error) {
 	multiNode, err := c.getSystemNode(ctx, bktInfo, corsFilename)
-	isErrNotFound := errors.Is(err, layer.ErrNodeNotFound)
+	isErrNotFound := errors.Is(err, layerErr.ErrNodeNotFound)
 	if err != nil && !isErrNotFound {
 		return nil, err
 	}
 
 	if isErrNotFound {
-		return nil, layer.ErrNoNodeToRemove
+		return nil, layerErr.ErrNoNodeToRemove
 	}
 
 	objToDelete := c.cleanOldNodes(ctx, multiNode.nodes, bktInfo)
@@ -730,7 +730,7 @@ func (c *Tree) GetBucketTagging(ctx context.Context, bktInfo *data.BucketInfo) (
 
 func (c *Tree) PutBucketTagging(ctx context.Context, bktInfo *data.BucketInfo, tagSet map[string]string) error {
 	multiNode, err := c.getSystemNode(ctx, bktInfo, bucketTaggingFilename)
-	isErrNotFound := errors.Is(err, layer.ErrNodeNotFound)
+	isErrNotFound := errors.Is(err, layerErr.ErrNodeNotFound)
 	if err != nil && !isErrNotFound {
 		return fmt.Errorf("couldn't get node: %w", err)
 	}
@@ -852,7 +852,7 @@ func getLatestVersionNode(nodes []NodeResponse) (NodeResponse, error) {
 	}
 
 	if targetIndexNode == -1 {
-		return nil, layer.ErrNodeNotFound
+		return nil, layerErr.ErrNodeNotFound
 	}
 
 	return nodes[targetIndexNode], nil
@@ -977,7 +977,7 @@ func (s *VersionsByPrefixStreamImpl) getNodeFromMainStream() (NodeResponse, erro
 	for {
 		node, err := s.mainStream.Next()
 		if err != nil {
-			if errors.Is(err, ErrNodeNotFound) {
+			if errors.Is(err, layerErr.ErrNodeNotFound) {
 				return nil, io.EOF
 			}
 			return nil, fmt.Errorf("main stream next: %w", err)
@@ -1104,7 +1104,7 @@ func (c *Tree) InitVersionsByPrefixStream(ctx context.Context, bktInfo *data.Buc
 func (c *Tree) getSubTreeByPrefixMainStream(ctx context.Context, bktInfo *data.BucketInfo, treeID, prefix string) (SubTreeStream, string, []uint64, error) {
 	rootID, tailPrefix, err := c.determinePrefixNode(ctx, bktInfo, treeID, prefix)
 	if err != nil {
-		if errors.Is(err, layer.ErrNodeNotFound) {
+		if errors.Is(err, layerErr.ErrNodeNotFound) {
 			return nil, "", nil, io.EOF
 		}
 		return nil, "", nil, err
@@ -1112,7 +1112,7 @@ func (c *Tree) getSubTreeByPrefixMainStream(ctx context.Context, bktInfo *data.B
 
 	subTree, err := c.service.GetSubTreeStream(ctx, bktInfo, treeID, rootID, 2)
 	if err != nil {
-		if errors.Is(err, layer.ErrNodeNotFound) {
+		if errors.Is(err, layerErr.ErrNodeNotFound) {
 			return nil, "", nil, io.EOF
 		}
 		return nil, "", nil, err
@@ -1158,7 +1158,7 @@ func (c *Tree) getPrefixNodeID(ctx context.Context, bktInfo *data.BucketInfo, tr
 	}
 
 	if len(intermediateNodes) == 0 {
-		return nil, layer.ErrNodeNotFound
+		return nil, layerErr.ErrNodeNotFound
 	}
 
 	return intermediateNodes, nil
@@ -1167,7 +1167,7 @@ func (c *Tree) getPrefixNodeID(ctx context.Context, bktInfo *data.BucketInfo, tr
 func (c *Tree) getSubTreeByPrefix(ctx context.Context, bktInfo *data.BucketInfo, treeID, prefix string, latestOnly bool) ([]NodeResponse, string, error) {
 	rootID, tailPrefix, err := c.determinePrefixNode(ctx, bktInfo, treeID, prefix)
 	if err != nil {
-		if errors.Is(err, layer.ErrNodeNotFound) {
+		if errors.Is(err, layerErr.ErrNodeNotFound) {
 			return nil, "", nil
 		}
 		return nil, "", err
@@ -1175,7 +1175,7 @@ func (c *Tree) getSubTreeByPrefix(ctx context.Context, bktInfo *data.BucketInfo,
 
 	subTree, err := c.service.GetSubTree(ctx, bktInfo, treeID, rootID, 2, false)
 	if err != nil {
-		if errors.Is(err, layer.ErrNodeNotFound) {
+		if errors.Is(err, layerErr.ErrNodeNotFound) {
 			return nil, "", nil
 		}
 		return nil, "", err
@@ -1281,7 +1281,7 @@ func (c *Tree) getUnversioned(ctx context.Context, bktInfo *data.BucketInfo, tre
 	}
 
 	if len(nodes) == 0 {
-		return nil, layer.ErrNodeNotFound
+		return nil, layerErr.ErrNodeNotFound
 	}
 
 	if len(nodes) > 1 {
@@ -1420,7 +1420,7 @@ func (c *Tree) GetMultipartUpload(ctx context.Context, bktInfo *data.BucketInfo,
 		}
 	}
 
-	return nil, layer.ErrNodeNotFound
+	return nil, layerErr.ErrNodeNotFound
 }
 
 func (c *Tree) AddPart(ctx context.Context, bktInfo *data.BucketInfo, multipartNodeID uint64, info *data.PartInfo) (oldObjIDsToDelete []oid.ID, err error) {
@@ -1498,7 +1498,7 @@ func (c *Tree) AddPart(ctx context.Context, bktInfo *data.BucketInfo, multipartN
 		return nil, err
 	}
 
-	return nil, layer.ErrNoNodeToRemove
+	return nil, layerErr.ErrNoNodeToRemove
 }
 
 func (c *Tree) GetParts(ctx context.Context, bktInfo *data.BucketInfo, multipartNodeID uint64) ([]*data.PartInfoExtended, error) {
@@ -1535,7 +1535,7 @@ func (c *Tree) GetParts(ctx context.Context, bktInfo *data.BucketInfo, multipart
 
 func (c *Tree) PutBucketLifecycleConfiguration(ctx context.Context, bktInfo *data.BucketInfo, addr oid.Address) ([]oid.Address, error) {
 	multiNode, err := c.getSystemNode(ctx, bktInfo, bucketLifecycleFilename)
-	isErrNotFound := errors.Is(err, layer.ErrNodeNotFound)
+	isErrNotFound := errors.Is(err, layerErr.ErrNodeNotFound)
 	if err != nil && !isErrNotFound {
 		return nil, fmt.Errorf("couldn't get node: %w", err)
 	}
@@ -1549,7 +1549,7 @@ func (c *Tree) PutBucketLifecycleConfiguration(ctx context.Context, bktInfo *dat
 		if _, err = c.service.AddNode(ctx, bktInfo, systemTree, 0, meta); err != nil {
 			return nil, err
 		}
-		return nil, layer.ErrNoNodeToRemove
+		return nil, layerErr.ErrNoNodeToRemove
 	}
 
 	latest := multiNode.Latest()
@@ -1584,13 +1584,13 @@ func (c *Tree) GetBucketLifecycleConfiguration(ctx context.Context, bktInfo *dat
 
 func (c *Tree) DeleteBucketLifecycleConfiguration(ctx context.Context, bktInfo *data.BucketInfo) ([]oid.Address, error) {
 	multiNode, err := c.getSystemNode(ctx, bktInfo, bucketLifecycleFilename)
-	isErrNotFound := errors.Is(err, layer.ErrNodeNotFound)
+	isErrNotFound := errors.Is(err, layerErr.ErrNodeNotFound)
 	if err != nil && !isErrNotFound {
 		return nil, err
 	}
 
 	if isErrNotFound {
-		return nil, layer.ErrNoNodeToRemove
+		return nil, layerErr.ErrNoNodeToRemove
 	}
 
 	objToDelete := c.cleanOldNodes(ctx, multiNode.nodes, bktInfo)
@@ -1727,7 +1727,7 @@ func (c *Tree) addVersion(ctx context.Context, bktInfo *data.BucketInfo, treeID
 			return node.ID, c.clearOutdatedVersionInfo(ctx, bktInfo, treeID, node.ID)
 		}
 
-		if !errors.Is(err, layer.ErrNodeNotFound) {
+		if !errors.Is(err, layerErr.ErrNodeNotFound) {
 			return 0, err
 		}
 	}
@@ -1760,7 +1760,7 @@ func (c *Tree) getVersions(ctx context.Context, bktInfo *data.BucketInfo, treeID
 	}
 	nodes, err := c.service.GetNodes(ctx, p)
 	if err != nil {
-		if errors.Is(err, layer.ErrNodeNotFound) {
+		if errors.Is(err, layerErr.ErrNodeNotFound) {
 			return nil, nil
 		}
 		return nil, err
@@ -1827,7 +1827,7 @@ func (c *Tree) getSystemNode(ctx context.Context, bktInfo *data.BucketInfo, name
 	nodes = filterMultipartNodes(nodes)
 
 	if len(nodes) == 0 {
-		return nil, layer.ErrNodeNotFound
+		return nil, layerErr.ErrNodeNotFound
 	}
 	if len(nodes) != 1 {
 		c.reqLogger(ctx).Warn(logs.FoundSeveralSystemNodes, zap.String("name", name))
diff --git a/pkg/service/tree/tree_client_in_memory.go b/pkg/service/tree/tree_client_in_memory.go
index 4c27fd7..a72ba5d 100644
--- a/pkg/service/tree/tree_client_in_memory.go
+++ b/pkg/service/tree/tree_client_in_memory.go
@@ -2,13 +2,14 @@ package tree
 
 import (
 	"context"
-	"errors"
+	stdErr "errors"
 	"fmt"
 	"io"
 	"sort"
 	"time"
 
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/data"
+	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer/errors"
 	"golang.org/x/exp/slices"
 )
 
@@ -242,16 +243,16 @@ func (c *ServiceClientMemory) GetSubTree(_ context.Context, bktInfo *data.Bucket
 
 	tr, ok := cnr.trees[treeID]
 	if !ok {
-		return nil, ErrNodeNotFound
+		return nil, errors.ErrNodeNotFound
 	}
 
 	if len(rootID) != 1 {
-		return nil, errors.New("invalid rootID")
+		return nil, stdErr.New("invalid rootID")
 	}
 
 	node := tr.treeData.getNode(rootID[0])
 	if node == nil {
-		return nil, ErrNodeNotFound
+		return nil, errors.ErrNodeNotFound
 	}
 
 	if sort {
@@ -282,21 +283,21 @@ func (s *SubTreeStreamMemoryImpl) Next() (NodeResponse, error) {
 func (c *ServiceClientMemory) GetSubTreeStream(_ context.Context, bktInfo *data.BucketInfo, treeID string, rootID []uint64, depth uint32) (SubTreeStream, error) {
 	cnr, ok := c.containers[bktInfo.CID.EncodeToString()]
 	if !ok {
-		return &SubTreeStreamMemoryImpl{err: ErrNodeNotFound}, nil
+		return &SubTreeStreamMemoryImpl{err: errors.ErrNodeNotFound}, nil
 	}
 
 	tr, ok := cnr.trees[treeID]
 	if !ok {
-		return nil, ErrNodeNotFound
+		return nil, errors.ErrNodeNotFound
 	}
 
 	if len(rootID) != 1 {
-		return nil, errors.New("invalid rootID")
+		return nil, stdErr.New("invalid rootID")
 	}
 
 	node := tr.treeData.getNode(rootID[0])
 	if node == nil {
-		return nil, ErrNodeNotFound
+		return nil, errors.ErrNodeNotFound
 	}
 
 	sortNode(tr.treeData)
@@ -353,7 +354,7 @@ func (c *ServiceClientMemory) AddNodeBase(_ context.Context, bktInfo *data.Bucke
 
 	parentNode := tr.treeData.getNode(parent)
 	if parentNode == nil {
-		return 0, ErrNodeNotFound
+		return 0, errors.ErrNodeNotFound
 	}
 
 	newID := tr.idCounter
@@ -418,22 +419,22 @@ func (c *ServiceClientMemory) AddNodeByPath(_ context.Context, bktInfo *data.Buc
 func (c *ServiceClientMemory) MoveNode(_ context.Context, bktInfo *data.BucketInfo, treeID string, nodeID, parentID uint64, meta map[string]string) error {
 	cnr, ok := c.containers[bktInfo.CID.EncodeToString()]
 	if !ok {
-		return ErrNodeNotFound
+		return errors.ErrNodeNotFound
 	}
 
 	tr, ok := cnr.trees[treeID]
 	if !ok {
-		return ErrNodeNotFound
+		return errors.ErrNodeNotFound
 	}
 
 	node := tr.treeData.getNode(nodeID)
 	if node == nil {
-		return ErrNodeNotFound
+		return errors.ErrNodeNotFound
 	}
 
 	newParent := tr.treeData.getNode(parentID)
 	if newParent == nil {
-		return ErrNodeNotFound
+		return errors.ErrNodeNotFound
 	}
 
 	node.data.meta = metaToNodeMeta(meta)
@@ -466,17 +467,17 @@ func sortNodes(list []*treeNodeMemory) {
 func (c *ServiceClientMemory) RemoveNode(_ context.Context, bktInfo *data.BucketInfo, treeID string, nodeID uint64) error {
 	cnr, ok := c.containers[bktInfo.CID.EncodeToString()]
 	if !ok {
-		return ErrNodeNotFound
+		return errors.ErrNodeNotFound
 	}
 
 	tr, ok := cnr.trees[treeID]
 	if !ok {
-		return ErrNodeNotFound
+		return errors.ErrNodeNotFound
 	}
 
 	node := tr.treeData.getNode(nodeID)
 	if node == nil {
-		return ErrNodeNotFound
+		return errors.ErrNodeNotFound
 	}
 
 	node.parent.removeChild(nodeID)