Starception

Beautiful exception page for Starlette and FastAPI apps.

Screenshot

Dark theme

Features

• secrets masking with reveal button
• solution hints
• exception notes (Python 3.11+)
• exception chains
• code snippets with syntax highlighting
• request info: query params, headers, cookies
• session contents
• request and app state
• platform information
• environment variables
• open paths in editor (VSCode; extensible via custom link templates)
• dark theme

Installation

pip install starception
# or with uv
uv add starception

With syntax highlighting

Install with the highlight extra for syntax-highlighted code snippets:

pip install starception[highlight]
# or with uv
uv add starception[highlight]

Usage

Starception works only in debug mode — make sure debug=True is set on your app.

Call install_error_handler before creating your application instance:

Starlette

from starception import install_error_handler
from starlette.applications import Starlette

install_error_handler()
app = Starlette(debug=True)

FastAPI

from starception import install_error_handler
from fastapi import FastAPI

install_error_handler()
app = FastAPI(debug=True)

See the example application in the examples/ directory for a full demo of all features.

Integration with other frameworks

Starception exports starception.exception_handler(request, exc), which you can use directly. Keep in mind that Starlette will not call custom exception handlers in debug mode — it always uses its built-in one.

The snippet below will not work as expected:

from starlette.applications import Starlette
from starception import exception_handler

app = Starlette(
    debug=True,
    exception_handlers={Exception: exception_handler}
)

Use install_error_handler() instead (shown above).

Secrets masking

Starception automatically masks values whose key contains key, secret, token, or password, and redacts passwords from URL-valued keys (e.g. database_url). Masked values are replaced with ******** and can be revealed by clicking the reveal button next to them.

Solution hints

If an exception class has a solution attribute, its content will be shown as a hint on the error page.

class DatabaseError(Exception):
    solution = (
        'The connection to the database cannot be established. '
        'Either the database server is down or connection credentials are invalid.'
    )

Exception notes

Python 3.11+ supports attaching notes to exceptions via add_note(). Starception displays them on the error page.

err = ValueError("something went wrong")
err.add_note("Check that the config file exists and is readable.")
raise err

Exception chains

When exceptions are chained — either explicitly (raise X from Y) or implicitly (raising inside an except block) — Starception renders each exception in the chain as a separate block, so you can trace the full error path.

Opening files in editor

Pass your editor to install_error_handler to make file paths in stack frames clickable:

from starception import install_error_handler

install_error_handler(editor='vscode')

Supported editors:

Custom link templates

Register any editor with add_link_template:

from starception import install_error_handler, add_link_template

add_link_template('zed', 'zed://file/{path}:{lineno}')
install_error_handler(editor='zed')

Dark theme

The error page supports light, dark, and auto (follows system preference) themes. The toggle is in the top-right corner of the page and the chosen theme is persisted across page loads.

Credits

• Look and feel inspired by Phoenix Framework.
• Icons by Tabler Icons.