flask-redantic 0.2.0

Automatic Pydantic validation and ReDoc documentation generation for Flask endpoints

flask-redantic

Automatic Pydantic validation and ReDoc API documentation for Flask.

flask-redantic is a Flask library that:

• Validates request bodies and query parameters by reading your type annotations
• Injects validated Pydantic model instances directly into your view functions
• Auto-generates interactive ReDoc API documentation - no YAML, no manual schema config
• Requires zero boilerplate - your annotations and docstrings are the source of truth

---

Installation

uv add flask-redantic

---

Quick Start

from flask import Flask, jsonify
from pydantic import BaseModel, Field
from flask_redantic import Redantic
from flask_redantic.raises import HTTP_404, HTTP_422

app = Flask(__name__)
api = Redantic(title="Quark's Bar API", version="v1.0")

class ItemIn(BaseModel):
    name: str = Field(..., min_length=1)
    category: str
    price_slips: int = Field(..., ge=0)

class ItemOut(BaseModel):
    id: int
    name: str
    category: str
    price_slips: int

class ErrorOut(BaseModel):
    message: str

@app.post("/inventory")
@api.validate(
    tags=["inventory"],
    raises=[HTTP_422()],
    success_status=201,
)
def create_item(body: ItemIn) -> ItemOut:
    """
    Acquire new stock for Quark's.

    The body is validated and injected automatically.
    """
    return jsonify({"id": 1, **body.model_dump()}), 201

@app.get("/inventory/<int:item_id>")
@api.validate(tags=["inventory"], raises=[HTTP_404(ErrorOut)])
def get_item(item_id: int) -> ItemOut:
    """Retrieve an item by ID."""
    item = db.get(item_id)
    if not item:
        return jsonify({"message": "Not found"}), 404
    return jsonify(item)

api.init_app(app)

Visit:

• http://localhost:5000/docs → Interactive ReDoc documentation
• http://localhost:5000/docs/openapi.json → Raw OpenAPI 3.0 JSON spec

---

How It Works

Everything is driven by standard Python type annotations:

Annotation	Effect
body: MyModel	JSON body validated → body is a MyModel instance
query: MyModel	Query-string params validated → query is a MyModel instance
item_id: int (Flask path param)	Passed through unchanged by Flask
-> MyModel	Documents the success response schema
raises=[HTTP_404(ErrorOut)]	Documents error response schemas

Body injection

@app.post("/inventory")
@api.validate(tags=["inventory"], success_status=201)
def create_item(body: ItemIn) -> ItemOut:
    # `body` is a fully validated ItemIn instance — ready to use
    return jsonify({"id": 1, **body.model_dump()}), 201

Body + path parameter

Flask path parameters are passed normally; flask-redantic injects body/query alongside them:

@app.put("/inventory/<int:item_id>")
@api.validate(tags=["inventory"], raises=[HTTP_404(ErrorOut)])
def update_item(item_id: int, body: ItemIn) -> ItemOut:
    # item_id comes from Flask routing
    # body is injected by redantic
    ...

Query parameters

Use a parameter named query annotated with a BaseModel:

class ItemFilter(BaseModel):
    category: str | None = None
    max_price: int | None = Field(None, ge=0)

@app.get("/inventory")
@api.validate(tags=["inventory"])
def list_items(query: ItemFilter) -> ItemOut:
    if query.category:
        ...

---

@api.validate Parameters

Parameter	Type	Description
raises	list[RaisesSpec]	Error response declarations (see below)
tags	list[str]	Group endpoints in the ReDoc sidebar
summary	str | None	One-line description. Auto-detected from first docstring line if omitted
deprecated	bool	Mark endpoint as deprecated in docs
success_status	int	Success HTTP status code (default: 200). Override to 201 for creation endpoints

Validation errors

When a request body or query fails validation, flask-redantic automatically returns:

HTTP 422 Unprocessable Entity

{
  "detail": [
    {
      "loc": ["name"],
      "msg": "String should have at least 1 character",
      "type": "string_too_short"
    }
  ]
}

---

raises — Declaring Error Responses

Import the pre-built HTTP error helpers from flask_redantic.raises:

from flask_redantic.raises import HTTP_400, HTTP_401, HTTP_403, HTTP_404, HTTP_409, HTTP_422, HTTP_500

@api.validate(raises=[
    HTTP_404(ErrorOut),   # 404 with ErrorOut schema
    HTTP_403(),           # 403 with no body
    HTTP_422,             # 422 with no body (no parentheses needed)
])
def my_endpoint(...): ...

Available helpers: HTTP_400, HTTP_401, HTTP_403, HTTP_404, HTTP_409, HTTP_422, HTTP_429, HTTP_500, HTTP_503

Note: A 422 Unprocessable Entity response is automatically added to the spec whenever a body or query model is present. You don't need to add it manually.

---

Application Factory Pattern

from flask_redantic import Redantic

api = Redantic(
    title="My API",
    version="v1.0",
    description="Supports **Markdown** in the overview section.",
    path="doc",   # /docs UI, /docs/openapi.json spec
)

from extensions import api
from flask import Flask

def create_app():
    app = Flask(__name__)
    # ... register routes ...
    api.init_app(app)   # call AFTER all routes are registered
    return app

---

Redantic Configuration

api = Redantic(
    app,               # optional Flask app; pass later via init_app()
    title="My API",    # shown in ReDoc header
    version="v2.0",    # shown in ReDoc version badge
    description="...", # Markdown shown in ReDoc overview
    path="doc",        # URL prefix; /docs UI, /docs/openapi.json spec
)

---

Running the Example

pip install -e .
python examples/app.py
# → http://localhost:5050/docs

---

Project Structure

flask-redantic/
├── src/flask_redantic/
│   ├── __init__.py    # Public API: Redantic
│   ├── core.py        # Redantic class + Flask Blueprint
│   ├── decorator.py   # @validate decorator + signature inspection
│   ├── spec.py        # OpenAPI 3.0 spec builder
│   ├── raises.py      # HTTP_xxx error-response helpers
│   └── templates.py   # ReDoc HTML template
└── examples/
    └── app.py         # Runnable Quark's Bar demo

---

License

MIT