Debug toolbar for Plain applications
Project description
plain.toolbar
A developer toolbar that displays debugging information in your browser.
Overview
The toolbar appears at the bottom of your browser window and shows useful debugging information about the current request. You can expand it to see detailed panels, switch between tabs, and resize it by dragging the top edge.
To render the toolbar, add the {% toolbar %} tag to your base template (typically just before the closing </body> tag):
<!DOCTYPE html>
<html>
<head>
<title>My App</title>
</head>
<body>
{% block content %}{% endblock %}
{% toolbar %}
</body>
</html>
The toolbar automatically hides itself in production unless the user is an admin. In debug mode, it always appears.
Built-in panels
Request panel
The Request panel shows information about the current HTTP request:
- Request ID
- Query parameters
- HTTP method
- View class
- URL pattern, name, args, and kwargs
- Template names (if available)
- Primary object (if the view has an
objectattribute)
Exception panel
When an exception occurs during request handling, the Exception panel automatically appears with:
- The exception type and message
- A color-coded traceback showing frames from your app, Plain, third-party packages, and Python stdlib
- Source code context around each frame (expandable/collapsible)
- Local variables for each frame (in debug mode)
- A "Copy" button to copy the full exception for sharing
- A "View raw" button to see the standard Python traceback format
- Clickable file paths that open in VS Code
App frames are highlighted in amber and expanded by default, making it easy to spot where the error occurred in your code.
Creating custom toolbar items
You can add your own panels to the toolbar by creating a ToolbarItem subclass and registering it with the @register_toolbar_item decorator.
Create a toolbar.py file in any installed app:
# app/users/toolbar.py
from plain.toolbar import ToolbarItem, register_toolbar_item
@register_toolbar_item
class UserToolbarItem(ToolbarItem):
name = "User"
panel_template_name = "toolbar/user.html"
def get_template_context(self):
context = super().get_template_context()
context["current_user"] = getattr(self.request, "user", None)
return context
Then create the panel template:
<!-- app/users/templates/toolbar/user.html -->
<div class="px-6 py-4 text-sm">
{% if current_user %}
<dl class="grid grid-cols-[max-content_1fr] gap-x-8 gap-y-2">
<dt>Email</dt>
<dd class="text-white/50">{{ current_user.email }}</dd>
<dt>ID</dt>
<dd class="text-white/50">{{ current_user.id }}</dd>
</dl>
{% else %}
<p class="text-white/50">No user logged in</p>
{% endif %}
</div>
The toolbar uses autodiscovery to find toolbar.py files in all installed apps.
Button-only items
You can also create toolbar items that only show a button in the minimized toolbar bar (no expandable panel). Set button_template_name instead of panel_template_name:
@register_toolbar_item
class QuickActionToolbarItem(ToolbarItem):
name = "QuickAction"
button_template_name = "toolbar/quick_action_button.html"
def is_enabled(self):
# Only show when a certain condition is met
return some_condition
Override is_enabled() to control when your toolbar item appears.
Visibility
The toolbar only renders when Toolbar.should_render() returns True. This happens when:
DEBUGisTrue, or- The user has
is_admin = True, or - An admin is impersonating another user (requires
plain.admin)
You can also temporarily hide the toolbar:
- Click the X button to hide it for the current session
- Click the clock icon to hide it for 1 hour (stored in localStorage)
- Call
plainToolbar.show()in the browser console to bring it back
JavaScript API
The toolbar exposes a window.plainToolbar object for programmatic control:
// Show/hide the toolbar
plainToolbar.show();
plainToolbar.hide();
// Expand/collapse the details panel
plainToolbar.expand();
plainToolbar.collapse();
plainToolbar.toggleExpand();
// Show a specific tab
plainToolbar.showTab("Request");
plainToolbar.showTab("Exception");
// Hide for a duration (milliseconds from now)
plainToolbar.hideUntil(Date.now() + 3600000); // Hide for 1 hour
// Reset custom height
plainToolbar.resetHeight();
FAQs
How do I style my custom panel?
The toolbar uses Tailwind CSS classes. Your panel template has access to all Tailwind utilities. The toolbar has a dark theme, so use light text colors like text-white, text-stone-300, or text-white/50 for muted text.
Can I add multiple custom panels?
Yes. Create multiple ToolbarItem subclasses, each with its own name and templates. They will appear as separate tabs in the toolbar.
Why does the Exception panel open automatically?
When an exception occurs, the toolbar automatically expands and shows the Exception panel so you can immediately see what went wrong. This behavior is intentional to surface errors quickly during development.
How do I disable the toolbar completely?
Remove plain.toolbar from your INSTALLED_PACKAGES setting. Alternatively, remove the {% toolbar %} tag from your templates.
Installation
Install the plain.toolbar package from PyPI:
uv add plain.toolbar
Add plain.toolbar to your INSTALLED_PACKAGES in app/settings.py:
INSTALLED_PACKAGES = [
# ... other packages
"plain.toolbar",
]
Add the {% toolbar %} template tag to your base template, just before the closing </body> tag:
<!DOCTYPE html>
<html>
<head>
<title>My App</title>
</head>
<body>
{% block content %}{% endblock %}
{% toolbar %}
</body>
</html>
A VERSION setting is required in your app/settings.py to display in the toolbar:
VERSION = "1.0.0"
The toolbar should now appear at the bottom of your browser window in debug mode.
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