Skip to main content

Waitress WSGI server

Project description

latest version of waitress on PyPI master Documentation Status IRC Freenode

Waitress is a production-quality pure-Python WSGI server with very acceptable performance. It has no dependencies except ones which live in the Python standard library. It runs on CPython on Unix and Windows under Python 3.7+. It is also known to run on PyPy 3 (version 3.7 compatible python) on UNIX. It supports HTTP/1.0 and HTTP/1.1.

For more information, see the “docs” directory of the Waitress package or visit



  • When expose_tracebacks is enabled waitress would fail to properly encode unicode thereby causing another error during error handling. See

  • Header length checking had a calculation that was done incorrectly when the data was received across multple socket reads. This calculation has been corrected, and no longer will Waitress send back a 413 Request Entity Too Large. See

Security Bugfix

  • in 2.1.0 a new feature was introduced that allowed the WSGI thread to start sending data to the socket. However this introduced a race condition whereby a socket may be closed in the sending thread while the main thread is about to call select() therey causing the entire application to be taken down. Waitress will no longer close the socket in the WSGI thread, instead waking up the main thread to cleanup. See


Security Bugfix

  • Waitress now validates that chunked encoding extensions are valid, and don’t contain invalid characters that are not allowed. They are still skipped/not processed, but if they contain invalid data we no longer continue in and return a 400 Bad Request. This stops potential HTTP desync/HTTP request smuggling. Thanks to Zhang Zeyu for reporting this issue. See

  • Waitress now validates that the chunk length is only valid hex digits when parsing chunked encoding, and values such as 0x01 and +01 are no longer supported. This stops potential HTTP desync/HTTP request smuggling. Thanks to Zhang Zeyu for reporting this issue. See

  • Waitress now validates that the Content-Length sent by a remote contains only digits in accordance with RFC7230 and will return a 400 Bad Request when the Content-Length header contains invalid data, such as +10 which would previously get parsed as 10 and accepted. This stops potential HTTP desync/HTTP request smuggling Thanks to Zhang Zeyu for reporting this issue. See


Python Version Support

  • Python 3.6 is no longer supported by Waitress

  • Python 3.10 is fully supported by Waitress



  • When the WSGI app starts sending data to the output buffer, we now attempt to send data directly to the socket. This avoids needing to wake up the main thread to start sending data. Allowing faster transmission of the first byte. See

    With thanks to Michael Merickel for being a great rubber ducky!

  • Add REQUEST_URI to the WSGI environment.

    REQUEST_URI is similar to request_uri in nginx. It is a string that contains the request path before separating the query string and decoding %-escaped characters.

Download files

Download the file for your platform. If you're not sure which to choose, learn more about installing packages.

Source Distribution

waitress-2.1.2.tar.gz (179.8 kB view hashes)

Uploaded source

Built Distribution

waitress-2.1.2-py3-none-any.whl (57.7 kB view hashes)

Uploaded py3

Supported by

AWS AWS Cloud computing and Security Sponsor Datadog Datadog Monitoring Fastly Fastly CDN Google Google Download Analytics Microsoft Microsoft PSF Sponsor Pingdom Pingdom Monitoring Sentry Sentry Error logging StatusPage StatusPage Status page