Basic Routing

A route connects a URL path to a Python function.

A minimal example

python

from flask import Flask
 
app = Flask(__name__)
 
 
@app.route("/")
def home():
    return "Home page"
 
 
@app.route("/about")
def about():
    return "About page"

Visiting / calls home()
Visiting /about calls about()

What can a route return?

A Flask view can return:

string → response body (HTML/text)
dict (Flask 2+) → JSON response
flask.Response object
tuple forms like (body, status_code) or (body, status_code, headers)

Example:

python

@app.route("/health")
def health():
    return {"status": "ok"}, 200

Trailing slash behavior

These behave differently:

/docs (no slash)
/docs/ (with slash)

Flask will often redirect automatically depending on how you define the route.

Best practice:

For “pages”: use /something/ style
For “resources/APIs”: use /api/items style

(Consistency matters more than the specific choice.)

Debugging tip: list all routes

The CLI command is extremely useful:

bash

flask routes

Visualize it

Here’s how Flask resolves an incoming URL to the view function that handles it.

diagram URL resolution flow mermaid

  flowchart LR
  U["Incoming request URL"] --> M["Flask URL map"]
  M --> V["Matched view function"]
  V --> R["Response returned"]

How Flask matches a request URL to a view function

🧪 Try It Yourself

Exercise 1 – Create a Flask App

Exercise 2 – Dynamic Route

Exercise 3 – Return JSON

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