Flask-OpenAPI3-Scalar

1.44.15 verified Fri May 01 auth: no python

Provides Scalar UI integration for flask-openapi3, allowing OpenAPI documentation to be rendered with Scalar's modern UI. Current version: 1.44.15. Release cadence: frequent updates.

pip install flask-openapi3-scalar

Common errors

error ModuleNotFoundError: No module named 'flask_openapi3_scalar' ↓

cause The package is not installed or installed incorrectly.

fix

Run 'pip install flask-openapi3-scalar' and ensure you use underscores in import.

error AttributeError: module 'flask_openapi3' has no attribute 'ScalarUI' ↓

cause Importing ScalarUI from flask_openapi3 instead of flask_openapi3_scalar.

fix

Change import to 'from flask_openapi3_scalar import ScalarUI'.

error TypeError: ScalarUI() missing 1 required positional argument: 'spec' ↓

cause The 'spec' argument is required but not provided.

fix

Pass the OpenAPI spec object: spec = api.get_spec(); ScalarUI(spec, ...).

Warnings

breaking The package was originally named 'flask-openapi3-scalar' but the import path may change. Ensure you use the correct module name 'flask_openapi3_scalar' (underscores). ↓

fix Use 'from flask_openapi3_scalar import ScalarUI' instead of hyphens.

gotcha The OpenAPI spec must be passed to ScalarUI. If you don't pass the spec, it may fail silently or show an empty UI. ↓

fix Always pass the spec object: ScalarUI(spec, ...) where spec is obtained from api.get_spec().

deprecated The 'url_prefix' parameter may be renamed or deprecated in future versions. Check changelog. ↓

fix Use the current parameter name as per documentation; if deprecated, use the new name.

Imports

ScalarUI
wrong
```
from flask_openapi3 import ScalarUI
```
correct
```
from flask_openapi3_scalar import ScalarUI
```
ScalarUI is in the separate plugin package, not in flask-openapi3 itself.
flask_openapi3_scalar
wrong
```
import flask_openapi3_scalar as SomethingElse
```
correct
```
import flask_openapi3_scalar
```
Common mistake: not using the correct module name. The module name is flask_openapi3_scalar.

Quickstart

Quickstart: create a Flask app with OpenAPI and register ScalarUI to serve interactive documentation at /scalar.

from flask import Flask
from flask_openapi3 import OpenAPI
from flask_openapi3_scalar import ScalarUI

app = Flask(__name__)
api = OpenAPI(app)
spec = api.get_spec()
ScalarUI(spec, url_prefix='/scalar').register(app)

@app.route('/')
def home():
    return 'Hello, World!'

if __name__ == '__main__':
    app.run()