Waitress WSGI Server

3.0.2 · active · verified Thu Apr 09

Waitress is a production-quality pure-Python WSGI server with a focus on simplicity and reliability. It's actively maintained by the Pylons Project, receiving frequent updates to support new Python versions and address security concerns. The current version is 3.0.2.

Warnings

breaking Waitress dropped support for Python 3.8 starting with version 3.0.1. Running on Python 3.8 or older will result in errors.
Fix: Upgrade your Python environment to 3.9 or newer. Python 3.13 is supported from v3.0.1.
breaking Waitress v3.0.2 changed how `trusted_proxy_headers` are handled for security. Untrusted values from proxy headers are now dropped, and Waitress *updates* the headers passed to the WSGI app with validated values. Applications might receive different, more secure header values than before, potentially breaking logic that relied on previously available, untrusted headers.
Fix: Review your application's reliance on `X-Forwarded-For`, `X-Forwarded-Proto`, etc. when `trusted_proxy_headers` is enabled. Ensure your proxy configuration and application logic are compatible with Waitress's new, stricter header processing.
breaking Starting with version 3.0.0, Waitress performs stricter validation of HTTP request methods and versions according to RFCs. Malformed requests that previously might have passed through could now be rejected with a 400 Bad Request.
Fix: Ensure client requests adhere to HTTP/1.0 or HTTP/1.1 specifications for methods and versions. Clients sending non-standard or malformed requests may need updates.
gotcha Waitress binds to `127.0.0.1` (localhost) by default. If you need to serve the application on a network interface accessible from other machines (e.g., in a Docker container or a public server), you must explicitly set the `host` parameter.
Fix: When calling `waitress.serve()`, pass `host='0.0.0.0'` (to bind to all available public interfaces) or the specific public IP address you want to bind to, e.g., `serve(app, host='0.0.0.0', port=8080)`.

Install

pip install waitress Install latest version

Imports

serve
```
from waitress import serve
```
The primary function to start the WSGI server.

Quickstart

This example demonstrates how to serve a minimal WSGI application using Waitress. It defines a simple WSGI callable `simple_app` and then uses `waitress.serve()` to run it on `127.0.0.1:8080`.

from waitress import serve

def simple_app(environ, start_response):
    """A barebones WSGI application."""
    status = '200 OK'
    headers = [('Content-type', 'text/plain; charset=utf-8')]
    start_response(status, headers)
    return [b"Hello from Waitress!"]

if __name__ == '__main__':
    print("Serving on http://127.0.0.1:8080")
    serve(simple_app, host='127.0.0.1', port=8080)

view raw JSON →