diff --git a/swh/core/api/__init__.py b/swh/core/api/__init__.py
--- a/swh/core/api/__init__.py
+++ b/swh/core/api/__init__.py
@@ -4,17 +4,20 @@
 # See top-level LICENSE file for more information
 
 from collections import abc
+import datetime
 import functools
 import inspect
 import json
 import logging
 import pickle
 import requests
-import datetime
+import traceback
 
-from typing import Any, ClassVar, Optional, Type
+from typing import Any, ClassVar, List, Optional, Type
 
 from flask import Flask, Request, Response, request, abort
+from werkzeug.exceptions import HTTPException
+
 from .serializers import (decode_response,
                           encode_data_client as encode_data,
                           msgpack_dumps, msgpack_loads, SWHJSONDecoder)
@@ -91,6 +94,15 @@
             super().__init__()
         self.response = response
 
+    def __str__(self):
+        if self.args and isinstance(self.args[0], dict) \
+                and 'type' in self.args[0] and 'args' in self.args[0]:
+            return (
+                f'<RemoteException {self.response.status_code} '
+                f'{self.args[0]["type"]}: {self.args[0]["args"]}>')
+        else:
+            return super().__str__()
+
 
 def remote_api_endpoint(path):
     def dec(f):
@@ -167,10 +179,18 @@
     """The exception class to raise in case of communication error with
     the server."""
 
+    reraise_exceptions: ClassVar[List[Type[Exception]]] = []
+    """On server errors, if any of the exception classes in this list
+    has the same name as the error name, then the exception will
+    be instantiated and raised instead of a generic RemoteException."""
+
     def __init__(self, url, api_exception=None,
-                 timeout=None, chunk_size=4096, **kwargs):
+                 timeout=None, chunk_size=4096,
+                 reraise_exceptions=None, **kwargs):
         if api_exception:
             self.api_exception = api_exception
+        if reraise_exceptions:
+            self.reraise_exceptions = reraise_exceptions
         base_url = url if url.endswith('/') else url + '/'
         self.url = base_url
         self.session = requests.Session()
@@ -242,8 +262,6 @@
         error; do nothing otherwise
 
         """
-        # XXX: unpickling below breaks language-independence and should be
-        # replaced by proper language-independent [de]serialization
         status_code = response.status_code
         status_class = response.status_code // 100
 
@@ -252,10 +270,21 @@
 
         exception = None
 
+        # TODO: only old servers send pickled error; stop trying to unpickle
+        # after they are all upgraded
         try:
             if status_class == 4:
                 data = decode_response(response)
-                exception = pickle.loads(data)
+                if isinstance(data, dict):
+                    for exc_type in self.reraise_exceptions:
+                        if exc_type.__name__ == data['exception']['type']:
+                            exception = exc_type(*data['exception']['args'])
+                            break
+                    else:
+                        exception = RemoteException(payload=data['exception'],
+                                                    response=response)
+                else:
+                    exception = pickle.loads(data)
 
             elif status_class == 5:
                 data = decode_response(response)
@@ -277,11 +306,8 @@
                 response=response)
 
     def _decode_response(self, response):
-        if response.status_code == 404:
-            return None
-        else:
-            self.raise_for_status(response)
-            return decode_response(response)
+        self.raise_for_status(response)
+        return decode_response(response)
 
     def __repr__(self):
         return '<{} url={}>'.format(self.__class__.__name__, self.url)
@@ -326,12 +352,23 @@
     return r
 
 
-def error_handler(exception, encoder):
-    # XXX: this breaks language-independence and should be
-    # replaced by proper serialization of errors
+def error_handler(exception, encoder, status_code=500):
     logging.exception(exception)
-    response = encoder(pickle.dumps(exception))
-    response.status_code = 400
+    tb = traceback.format_exception(None, exception, exception.__traceback__)
+    error = {
+        'exception': {
+            'type': type(exception).__name__,
+            'args': exception.args,
+            'message': str(exception),
+            'traceback': tb,
+        }
+    }
+    response = encoder(error)
+    if isinstance(exception, HTTPException):
+        response.status_code = exception.code
+    else:
+        # TODO: differentiate between server errors and client errors
+        response.status_code = status_code
     return response
 
 
diff --git a/swh/core/api/tests/test_rpc_client_server.py b/swh/core/api/tests/test_rpc_client_server.py
--- a/swh/core/api/tests/test_rpc_client_server.py
+++ b/swh/core/api/tests/test_rpc_client_server.py
@@ -6,7 +6,7 @@
 import pytest
 
 from swh.core.api import remote_api_endpoint, RPCServerApp, RPCClient
-from swh.core.api import error_handler, encode_data_server
+from swh.core.api import error_handler, encode_data_server, RemoteException
 
 
 # this class is used on the server part
@@ -79,7 +79,7 @@
 def test_api_server_endpoint_missing(swh_rpc_client):
     # A 'missing' endpoint (server-side) should raise an exception
     # due to a 404, since at the end, we do a GET/POST an inexistent URL
-    with pytest.raises(Exception, match='404 Not Found'):
+    with pytest.raises(Exception, match='404 not found'):
         swh_rpc_client.not_on_server()
 
 
@@ -98,5 +98,10 @@
 
 
 def test_api_typeerror(swh_rpc_client):
-    with pytest.raises(TypeError, match='Did I pass through?'):
+    with pytest.raises(RemoteException) as exc_info:
         swh_rpc_client.raise_typeerror()
+
+    assert exc_info.value.args[0]['type'] == 'TypeError'
+    assert exc_info.value.args[0]['args'] == ['Did I pass through?']
+    assert str(exc_info.value) \
+        == "<RemoteException 500 TypeError: ['Did I pass through?']>"