diff --git a/rio/cli/run_project/app_loading.py b/rio/cli/run_project/app_loading.py
index 4a7d7ae1..b48d6692 100644
--- a/rio/cli/run_project/app_loading.py
+++ b/rio/cli/run_project/app_loading.py
@@ -1,9 +1,6 @@
 import functools
 import html
-import itertools
-import os
 import sys
-import traceback
 import types
 import typing as t
 from pathlib import Path
@@ -14,8 +11,7 @@ import rio
 import rio.app_server.fastapi_server
 import rio.global_state
 
-from ... import icon_registry, project_config
-from .. import nice_traceback
+from ... import icon_registry, nice_traceback, project_config
 
 
 class AppLoadError(Exception):
@@ -27,24 +23,6 @@ class AppLoadError(Exception):
         return self.args[0]
 
 
-def remove_rio_internals_from_traceback(
-    tb: list[traceback.FrameSummary],
-) -> t.Sequence[traceback.FrameSummary]:
-    # Skip frames which are internal to rio (or libraries used by rio) until we
-    # hit the first non-rio frame. Then include everything.
-    rio_root = rio.__file__
-    assert rio_root.endswith(os.sep + "__init__.py")
-    rio_root = rio_root.removesuffix(os.sep + "__init__.py")
-
-    def predicate(frame: traceback.FrameSummary) -> bool:
-        return (
-            frame.filename.startswith((rio_root, "<frozen importlib"))
-            or frame.filename == path_imports.__file__
-        )
-
-    return list(itertools.dropwhile(predicate, tb))
-
-
 def make_traceback_html(
     *,
     err: t.Union[str, BaseException],
@@ -58,7 +36,6 @@ def make_traceback_html(
         traceback_html = nice_traceback.format_exception_html(
             err,
             relpath=project_directory,
-            preprocess_traceback=remove_rio_internals_from_traceback,
         )
 
     return f"""
diff --git a/rio/cli/run_project/arbiter.py b/rio/cli/run_project/arbiter.py
index b60aa17a..9abd7082 100644
--- a/rio/cli/run_project/arbiter.py
+++ b/rio/cli/run_project/arbiter.py
@@ -19,9 +19,8 @@ import rio.arequests as arequests
 import rio.cli
 import rio.snippets
 
-from ... import project_config, utils, version
+from ... import nice_traceback, project_config, utils, version
 from ...debug.monkeypatches import apply_monkeypatches
-from .. import nice_traceback
 from . import (
     app_loading,
     file_watcher_worker,
@@ -306,12 +305,9 @@ class Arbiter:
             revel.error(f"The app could not be loaded: {err}")
 
             if err.__cause__ is not None:
-                revel.print(
-                    nice_traceback.format_exception_revel(
-                        err.__cause__,
-                        relpath=self.proj.project_directory,
-                        preprocess_traceback=app_loading.remove_rio_internals_from_traceback,
-                    )
+                nice_traceback.print_exception(
+                    err.__cause__,
+                    relpath=self.proj.project_directory,
                 )
 
             # If running in release mode, no further attempts to load the app
@@ -454,7 +450,7 @@ class Arbiter:
             revel.error("The arbiter has crashed.")
             revel.error("This is a bug in Rio - please report it")
             print()
-            revel.print(nice_traceback.format_exception_revel(err))
+            nice_traceback.print_exception(err)
 
             rio.cli._logger.exception("The arbiter has crashed")
 
diff --git a/rio/cli/run_project/uvicorn_worker.py b/rio/cli/run_project/uvicorn_worker.py
index 43ee3024..3302b166 100644
--- a/rio/cli/run_project/uvicorn_worker.py
+++ b/rio/cli/run_project/uvicorn_worker.py
@@ -11,8 +11,7 @@ import rio
 import rio.app_server.fastapi_server
 import rio.cli
 
-from ... import utils
-from .. import nice_traceback
+from ... import nice_traceback, utils
 from . import run_models
 
 
@@ -110,8 +109,7 @@ class UvicornWorker:
             rio.cli._logger.exception(f"Uvicorn has crashed")
 
             revel.error(f"Uvicorn has crashed:")
-            print()
-            revel.print(nice_traceback.format_exception_revel(err))
+            nice_traceback.print_exception(err)
             self.push_event(run_models.StopRequested())
         finally:
             rio.cli._logger.debug("Requesting uvicorn to exit")
diff --git a/rio/cli/nice_traceback.py b/rio/nice_traceback.py
similarity index 87%
rename from rio/cli/nice_traceback.py
rename to rio/nice_traceback.py
index f08043d3..d2f59ab1 100644
--- a/rio/cli/nice_traceback.py
+++ b/rio/nice_traceback.py
@@ -6,14 +6,33 @@ but is colored and just tweaked in general.
 import dataclasses
 import html
 import io
+import itertools
 import linecache
+import os
 import sys
 import traceback
 import typing as t
 from pathlib import Path
 
+import path_imports
 import revel
 
+import rio
+
+__all__ = [
+    "format_exception_revel",
+    "format_exception_html",
+    "FormatStyle",
+    "print_exception",
+]
+
+
+def print_exception(
+    error: BaseException, *, relpath: Path | None = None
+) -> None:
+    text = format_exception_revel(error, relpath=relpath)
+    revel.print(text)
+
 
 @dataclasses.dataclass
 class FormatStyle:
@@ -60,6 +79,24 @@ def _handle_syntax_error(err: SyntaxError) -> traceback.FrameSummary:
         )
 
 
+def remove_rio_internals_from_traceback(
+    tb: list[traceback.FrameSummary],
+) -> t.Sequence[traceback.FrameSummary]:
+    # Skip frames which are internal to rio (or libraries used by rio) until we
+    # hit the first non-rio frame. Then include everything.
+    rio_root = rio.__file__
+    assert rio_root.endswith(os.sep + "__init__.py")
+    rio_root = rio_root.removesuffix(os.sep + "__init__.py")
+
+    def predicate(frame: traceback.FrameSummary) -> bool:
+        return (
+            frame.filename.startswith((rio_root, "<frozen importlib"))
+            or frame.filename == path_imports.__file__
+        )
+
+    return list(itertools.dropwhile(predicate, tb))
+
+
 def _format_single_exception_raw(
     out: t.IO[str],
     err: BaseException,
@@ -67,9 +104,6 @@ def _format_single_exception_raw(
     include_header: bool,
     style: FormatStyle,
     relpath: Path | None,
-    preprocess_traceback: t.Callable[
-        [list[traceback.FrameSummary]], t.Sequence[traceback.FrameSummary]
-    ],
 ) -> None:
     """
     Format a single exception and write it to the output stream.
@@ -81,7 +115,7 @@ def _format_single_exception_raw(
     if isinstance(err, SyntaxError):
         tb_list.append(_handle_syntax_error(err))
 
-    tb_list = preprocess_traceback(tb_list)
+    tb_list = remove_rio_internals_from_traceback(tb_list)
 
     # TODO: Add special handling for recursion errors. Instead of printing the
     # same frame 1000 times, print a message like "Last 5 frames repeated 200
@@ -164,9 +198,6 @@ def format_exception_raw(
     *,
     style: FormatStyle,
     relpath: Path | None = None,
-    preprocess_traceback: t.Callable[
-        [list[traceback.FrameSummary]], t.Sequence[traceback.FrameSummary]
-    ] = lambda tb: tb,
 ) -> str:
     """
     Format an exception into a pretty string with the given style.
@@ -198,7 +229,6 @@ def format_exception_raw(
             include_header=include_header,
             style=style,
             relpath=relpath,
-            preprocess_traceback=preprocess_traceback,
         )
 
     # Format
@@ -211,9 +241,6 @@ def format_exception_revel(
     err: BaseException,
     *,
     relpath: Path | None = None,
-    preprocess_traceback: t.Callable[
-        [list[traceback.FrameSummary]], t.Sequence[traceback.FrameSummary]
-    ] = lambda tb: tb,
 ) -> str:
     """
     Format an exception using revel's styling.
@@ -237,7 +264,6 @@ def format_exception_revel(
         err,
         style=style,
         relpath=relpath,
-        preprocess_traceback=preprocess_traceback,
     )
 
 
@@ -245,9 +271,6 @@ def format_exception_html(
     err: BaseException,
     *,
     relpath: Path | None = None,
-    preprocess_traceback: t.Callable[
-        [list[traceback.FrameSummary]], t.Sequence[traceback.FrameSummary]
-    ] = lambda tb: tb,
 ) -> str:
     """
     Format an exception into HTML with appropriate styling.
@@ -271,7 +294,6 @@ def format_exception_html(
         err,
         style=style,
         relpath=relpath,
-        preprocess_traceback=preprocess_traceback,
     )
 
     # HTML-ify newlines
diff --git a/rio/session.py b/rio/session.py
index 2166e278..a72a0bab 100644
--- a/rio/session.py
+++ b/rio/session.py
@@ -16,7 +16,9 @@ import typing as t
 import weakref
 from datetime import tzinfo
 
+import introspection
 import ordered_set
+import revel
 import starlette.datastructures
 import unicall
 import uniserde
@@ -33,6 +35,7 @@ from . import (
     fills,
     global_state,
     inspection,
+    nice_traceback,
     routing,
     serialization,
     session_attachments,
@@ -864,9 +867,9 @@ window.resizeTo(screen.availWidth, screen.availHeight);
                 await result
 
         # Display and discard exceptions
-        except Exception:
-            print("Exception in event handler:")
-            traceback.print_exc()
+        except Exception as error:
+            revel.error("Exception in event handler:")
+            nice_traceback.print_exception(error)
 
         if refresh:
             await self._refresh()
@@ -2318,6 +2321,7 @@ window.history.{method}(null, "", {json.dumps(relative_url)})
         new_name="file_types",
     )
     @deprecations.deprecated(since="0.10", replacement=pick_file)
+    @introspection.set_signature(pick_file)
     async def file_chooser(
         self,
         *args,