Error index

Find your error by the words in the message. Use your browser's find-in-page (Ctrl+F) or the site search with a distinctive phrase from the error, in quotes.

By message text

The message contains	Go to
points to non-existent page	Link or button points to an unknown route
expects a value for parameter ... but none was provided	Route is missing a parameter a form expected
expects int but got	Could not convert text to an int
expects float but got, or another type	Could not convert a value to the parameter's type
type changed from ... to ...	State doesn't match the State class
must be a list of strings or components	Page content must be a list of strings or components
Two components share a name	Two components share a name
SelectBox default not among the options	SelectBox default not in options
Header level must be between 1 and 6	Header level must be 1-6
Circular Reference in a generated test	Circular Reference appears in generated tests
A file does not look like unicode (utf-8) text	Uploaded file couldn't be read as text
404 for an image or file on the deployed site	Image or file works locally but 404s when deployed
A red X on your GitHub deployment	GitHub Actions build failed
An import fails in the browser	A library import fails in the browser
Camera, microphone, or location permission denied	Device permission denied

Not an error, but broken anyway

• If code placed after start_server() never runs, nothing is wrong: that is how start_server works.
• If there is no error message but the app behaves incorrectly, see Troubleshooting, which is organized by symptom.

Python's own errors

SyntaxError, NameError, TypeError, IndexError, and similar messages come from Python itself, not from Drafter. Drafter's error page explains the common ones in plain language above the traceback. Read that friendly explanation first, then go to the line it names. The habits in Reading an error page apply here as well.

How these pages work

Every entry follows the same eight steps: the error verbatim, what it means, where to look, how to check which cause you have, the fix, how to confirm, how to prevent it, and a link to the concept page that addresses the underlying misunderstanding. If your error is not listed and the friendly message does not resolve the problem, consider a bug report; this index grows from the errors students actually encounter.