Waitress is meant to be 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 2.7+ and Python 3.3+. It is also known to run on PyPy 1.6.0 on UNIX. It supports HTTP/1.0 and HTTP/1.1.


Here’s normal usage of the server:

from waitress import serve
serve(wsgiapp, listen='*:8080')

This will run waitress on port 8080 on all available IP addresses, both IPv4 and IPv6.

from waitress import serve
serve(wsgiapp, host='', port=8080)

This will run waitress on port 8080 on all available IPv4 addresses.

If you want to serve your application on all IP addresses, on port 8080, you can omit the host and port arguments and just call serve with the WSGI app as a single argument:

from waitress import serve

Press Ctrl-C (or Ctrl-Break on Windows) to exit the server.

The default is to bind to any IPv4 address on port 8080:

from waitress import serve

If you want to serve your application through a UNIX domain socket (to serve a downstream HTTP server/proxy, e.g. nginx, lighttpd, etc.), call serve with the unix_socket argument:

from waitress import serve
serve(wsgiapp, unix_socket='/path/to/unix.sock')

Needless to say, this configuration won’t work on Windows.

Exceptions generated by your application will be shown on the console by default. See Logging to change this.

There’s an entry point for PasteDeploy (egg:waitress#main) that lets you use Waitress’s WSGI gateway from a configuration file, e.g.:

use = egg:waitress#main
listen =

Using host and port is also supported:

host =
port = 8080

The PasteDeploy syntax for UNIX domain sockets is analagous:

use = egg:waitress#main
unix_socket = /path/to/unix.sock

You can find more settings to tweak (arguments to waitress.serve or equivalent settings in PasteDeploy) in Arguments to waitress.serve.

Additionally, there is a command line runner called waitress-serve, which can be used in development and in situations where the likes of PasteDeploy is not necessary:

# Listen on both IPv4 and IPv6 on port 8041
waitress-serve --listen=*:8041 myapp:wsgifunc

# Listen on only IPv4 on port 8041
waitress-serve --port=8041 myapp:wsgifunc

For more information on this, see waitress-serve.


waitress.serve calls logging.basicConfig() to set up logging to the console when the server starts up. Assuming no other logging configuration has already been done, this sets the logging default level to logging.WARNING. The Waitress logger will inherit the root logger’s level information (it logs at level WARNING or above).

Waitress sends its logging output (including application exception renderings) to the Python logger object named waitress. You can influence the logger level and output stream using the normal Python logging module API. For example:

import logging
logger = logging.getLogger('waitress')

Within a PasteDeploy configuration file, you can use the normal Python logging module .ini file format to change similar Waitress logging options. For example:

level = INFO

Using Behind a Reverse Proxy

Often people will set up “pure Python” web servers behind reverse proxies, especially if they need SSL support (Waitress does not natively support SSL). Even if you don’t need SSL support, it’s not uncommon to see Waitress and other pure-Python web servers set up to “live” behind a reverse proxy; these proxies often have lots of useful deployment knobs.

If you’re using Waitress behind a reverse proxy, you’ll almost always want your reverse proxy to pass along the Host header sent by the client to Waitress, in either case, as it will be used by most applications to generate correct URLs.

For example, when using Nginx as a reverse proxy, you might add the following lines in a location section:

proxy_set_header        Host $host;

The Apache directive named ProxyPreserveHost does something similar when used as a reverse proxy.

Unfortunately, even if you pass the Host header, the Host header does not contain enough information to regenerate the original URL sent by the client. For example, if your reverse proxy accepts HTTPS requests (and therefore URLs which start with https://), the URLs generated by your application when used behind a reverse proxy served by Waitress might inappropriately be http://foo rather than https://foo. To fix this, you’ll want to change the wsgi.url_scheme in the WSGI environment before it reaches your application. You can do this in one of three ways:

  1. You can pass a url_scheme configuration variable to the waitress.serve function.
  2. You can configure the proxy reverse server to pass a header, X_FORWARDED_PROTO, whose value will be set for that request as the wsgi.url_scheme environment value. Note that you must also conigure waitress.serve by passing the IP address of that proxy as its trusted_proxy.
  3. You can use Paste’s PrefixMiddleware in conjunction with configuration settings on the reverse proxy server.

Using url_scheme to set wsgi.url_scheme

You can have the Waitress server use the https url scheme by default.:

from waitress import serve
serve(wsgiapp, listen='', url_scheme='https')

This works if all URLs generated by your application should use the https scheme.

Passing the X_FORWARDED_PROTO header to set wsgi.url_scheme

If your proxy accepts both HTTP and HTTPS URLs, and you want your application to generate the appropriate url based on the incoming scheme, also set up your proxy to send a X-Forwarded-Proto with the original URL scheme along with each proxied request. For example, when using Nginx:

proxy_set_header        X-Forwarded-Proto $scheme;

or via Apache:

RequestHeader set X-Forwarded-Proto https


You must also configure the Waitress server’s trusted_proxy to contain the IP address of the proxy in order for this header to override the default URL scheme.

Using url_prefix to influence SCRIPT_NAME and PATH_INFO

You can have the Waitress server use a particular url prefix by default for all URLs generated by downstream applications that take SCRIPT_NAME into account.:

from waitress import serve
serve(wsgiapp, listen='', url_prefix='/foo')

Setting this to any value except the empty string will cause the WSGI SCRIPT_NAME value to be that value, minus any trailing slashes you add, and it will cause the PATH_INFO of any request which is prefixed with this value to be stripped of the prefix. This is useful in proxying scenarios where you wish to forward all traffic to a Waitress server but need URLs generated by downstream applications to be prefixed with a particular path segment.

Using Paste’s PrefixMiddleware to set wsgi.url_scheme

If only some of the URLs generated by your application should use the https scheme (and some should use http), you’ll need to use Paste’s PrefixMiddleware as well as change some configuration settings on your proxy. To use PrefixMiddleware, wrap your application before serving it using Waitress:

from waitress import serve
from paste.deploy.config import PrefixMiddleware
app = PrefixMiddleware(app)

Once you wrap your application in the the PrefixMiddleware, the middleware will notice certain headers sent from your proxy and will change the wsgi.url_scheme and possibly other WSGI environment variables appropriately.

Once your application is wrapped by the prefix middleware, you should instruct your proxy server to send along the original Host header from the client to your Waitress server, as well as sending along a X-Forwarded-Proto header with the appropriate value for wsgi.url_scheme.

If your proxy accepts both HTTP and HTTPS URLs, and you want your application to generate the appropriate url based on the incoming scheme, also set up your proxy to send a X-Forwarded-Proto with the original URL scheme along with each proxied request. For example, when using Nginx:

proxy_set_header        X-Forwarded-Proto $scheme;

It’s permitted to set an X-Forwarded-For header too; the PrefixMiddleware uses this to adjust other environment variables (you’ll have to read its docs to find out which ones, I don’t know what they are). For the X-Forwarded-For header:

proxy_set_header        X-Forwarded-For $proxy_add_x_forwarded_for;

Note that you can wrap your application in the PrefixMiddleware declaratively in a PasteDeploy configuration file too, if your web framework uses PasteDeploy-style configuration:

use = egg:mypackage#myapp

use = egg:PasteDeploy#prefix

pipeline =

use = egg:waitress#main
listen =

Note that you can also set PATH_INFO and SCRIPT_NAME using PrefixMiddleware too (its original purpose, really) instead of using Waitress’ url_prefix adjustment. See the PasteDeploy docs for more information.

Change History

1.1.0 (2017-10-10)


  • Waitress now has a __main__ and thus may be called with python -mwaitress


1.0.2 (2017-02-04)


  • Python 3.6 is now officially supported in Waitress


  • Add a work-around for libc issue on Linux not following the documented standards. If getnameinfo() fails because of DNS not being available it should return the IP address instead of the reverse DNS entry, however instead getnameinfo() raises. We catch this, and ask getnameinfo() for the same information again, explicitly asking for IP address instead of reverse DNS hostname. See https://github.com/Pylons/waitress/issues/149 and https://github.com/Pylons/waitress/pull/153

1.0.1 (2016-10-22)


  • IPv6 support on Windows was broken due to missing constants in the socket module. This has been resolved by setting the constants on Windows if they are missing. See https://github.com/Pylons/waitress/issues/138
  • A ValueError was raised on Windows when passing a string for the port, on Windows in Python 2 using service names instead of port numbers doesn’t work with getaddrinfo. This has been resolved by attempting to convert the port number to an integer, if that fails a ValueError will be raised. See https://github.com/Pylons/waitress/issues/139

1.0.0 (2016-08-31)


  • Removed AI_ADDRCONFIG from the call to getaddrinfo, this resolves an issue whereby getaddrinfo wouldn’t return any addresses to bind to on hosts where there is no internet connection but localhost is requested to be bound to. See https://github.com/Pylons/waitress/issues/131 for more information.


  • Python 2.6 is no longer supported.


  • IPv6 support

  • Waitress is now able to listen on multiple sockets, including IPv4 and IPv6. Instead of passing in a host/port combination you now provide waitress with a space delineated list, and it will create as many sockets as required.

    from waitress import serve
    serve(wsgiapp, listen=' [::]:9090 *:6543')


0.9.0 (2016-04-15)


  • Python 3.2 is no longer supported by Waitress.
  • Python 2.6 will no longer be supported by Waitress in future releases.



0.8.10 (2015-09-02)

  • Add support for Python 3.4, 3.5b2, and PyPy3.
  • Use a nonglobal asyncore socket map by default, trying to prevent conflicts with apps and libs that use the asyncore global socket map ala https://github.com/Pylons/waitress/issues/63. You can get the old use-global-socket-map behavior back by passing asyncore.socket_map to the create_server function as the map argument.
  • Waitress violated PEP 3333 with respect to reraising an exception when start_response was called with an exc_info argument. It would reraise the exception even if no data had been sent to the client. It now only reraises the exception if data has actually been sent to the client. See https://github.com/Pylons/waitress/pull/52 and https://github.com/Pylons/waitress/issues/51
  • Add a docs section to tox.ini that, when run, ensures docs can be built.
  • If an application value of None is supplied to the create_server constructor function, a ValueError is now raised eagerly instead of an error occuring during runtime. See https://github.com/Pylons/waitress/pull/60
  • Fix parsing of multi-line (folded) headers. See https://github.com/Pylons/waitress/issues/53 and https://github.com/Pylons/waitress/pull/90
  • Switch from the low level Python thread/_thread module to the threading module.
  • Improved exception information should module import go awry.

0.8.9 (2014-05-16)

  • Fix tests under Windows. NB: to run tests under Windows, you cannot run “setup.py test” or “setup.py nosetests”. Instead you must run python.exe -c "import nose; nose.main()". If you try to run the tests using the normal method under Windows, each subprocess created by the test suite will attempt to run the test suite again. See https://github.com/nose-devs/nose/issues/407 for more information.
  • Give the WSGI app_iter generated when wsgi.file_wrapper is used (ReadOnlyFileBasedBuffer) a close method. Do not call close on an instance of such a class when it’s used as a WSGI app_iter, however. This is part of a fix which prevents a leakage of file descriptors; the other part of the fix was in WebOb (https://github.com/Pylons/webob/commit/951a41ce57bd853947f842028bccb500bd5237da).
  • Allow trusted proxies to override wsgi.url_scheme via a request header, X_FORWARDED_PROTO. Allows proxies which serve mixed HTTP / HTTPS requests to control signal which are served as HTTPS. See https://github.com/Pylons/waitress/pull/42.

0.8.8 (2013-11-30)

  • Fix some cases where the creation of extremely large output buffers (greater than 2GB, suspected to be buffers added via wsgi.file_wrapper) might cause an OverflowError on Python 2. See https://github.com/Pylons/waitress/issues/47.
  • When the url_prefix adjustment starts with more than one slash, all slashes except one will be stripped from its beginning. This differs from older behavior where more than one leading slash would be preserved in url_prefix.
  • If a client somehow manages to send an empty path, we no longer convert the empty path to a single slash in PATH_INFO. Instead, the path remains empty. According to RFC 2616 section “5.1.2 Request-URI”, the scenario of a client sending an empty path is actually not possible because the request URI portion cannot be empty.
  • If the url_prefix adjustment matches the request path exactly, we now compute SCRIPT_NAME and PATH_INFO properly. Previously, if the url_prefix was /foo and the path received from a client was /foo, we would set both SCRIPT_NAME and PATH_INFO to /foo. This was incorrect. Now in such a case we set PATH_INFO to the empty string and we set SCRIPT_NAME to /foo. Note that the change we made has no effect on paths that do not match the url_prefix exactly (such as /foo/bar); these continue to operate as they did. See https://github.com/Pylons/waitress/issues/46
  • Preserve header ordering of headers with the same name as per RFC 2616. See https://github.com/Pylons/waitress/pull/44
  • When waitress receives a Transfer-Encoding: chunked request, we no longer send the TRANSFER_ENCODING nor the HTTP_TRANSFER_ENCODING value to the application in the environment. Instead, we pop this header. Since we cope with chunked requests by buffering the data in the server, we also know when a chunked request has ended, and therefore we know the content length. We set the content-length header in the environment, such that applications effectively never know the original request was a T-E: chunked request; it will appear to them as if the request is a non-chunked request with an accurate content-length.
  • Cope with the fact that the Transfer-Encoding value is case-insensitive.
  • When the --unix-socket-perms option was used as an argument to waitress-serve, a TypeError would be raised. See https://github.com/Pylons/waitress/issues/50.

0.8.7 (2013-08-29)

  • The HTTP version of the response returned by waitress when it catches an exception will now match the HTTP request version.
  • Fix: CONNECTION header will be HTTP_CONNECTION and not CONNECTION_TYPE (see https://github.com/Pylons/waitress/issues/13)

0.8.6 (2013-08-12)

  • Do alternate type of checking for UNIX socket support, instead of checking for platform == windows.
  • Functional tests now use multiprocessing module instead of subprocess module, speeding up test suite and making concurrent execution more reliable.
  • Runner now appends the current working directory to sys.path to support running WSGI applications from a directory (i.e., not installed in a virtualenv).
  • Add a url_prefix adjustment setting. You can use it by passing script_name='/foo' to waitress.serve or you can use it in a PasteDeploy ini file as script_name = /foo. This will cause the WSGI SCRIPT_NAME value to be the value passed minus any trailing slashes you add, and it will cause the PATH_INFO of any request which is prefixed with this value to be stripped of the prefix. You can use this instead of PasteDeploy’s prefixmiddleware to always prefix the path.

0.8.5 (2013-05-27)

  • Fix runner multisegment imports in some Python 2 revisions (see https://github.com/Pylons/waitress/pull/34).
  • For compatibility, WSGIServer is now an alias of TcpWSGIServer. The signature of BaseWSGIServer is now compatible with WSGIServer pre-0.8.4.

0.8.4 (2013-05-24)

  • Add a command-line runner called waitress-serve to allow Waitress to run WSGI applications without any addional machinery. This is essentially a thin wrapper around the waitress.serve() function.
  • Allow parallel testing (e.g., under detox or nosetests --processes) using PID-dependent port / socket for functest servers.
  • Fix integer overflow errors on large buffers. Thanks to Marcin Kuzminski for the patch. See: https://github.com/Pylons/waitress/issues/22
  • Add support for listening on Unix domain sockets.

0.8.3 (2013-04-28)


  • Add an asyncore_loop_timeout adjustment value, which controls the timeout value passed to asyncore.loop; defaults to 1.

Bug Fixes

0.8.2 (2012-11-14)

Bug Fixes

  • http://corte.si/posts/code/pathod/pythonservers/index.html pointed out that sending a bad header resulted in an exception leading to a 500 response instead of the more proper 400 response without an exception.
  • Fix a race condition in the test suite.
  • Allow “ident” to be used as a keyword to serve() as per docs.
  • Add py33 to tox.ini.

0.8.1 (2012-02-13)

Bug Fixes

  • A brown-bag bug prevented request concurrency. A slow request would block subsequent the responses of subsequent requests until the slow request’s response was fully generated. This was due to a “task lock” being declared as a class attribute rather than as an instance attribute on HTTPChannel. Also took the opportunity to move another lock named “outbuf lock” to the channel instance rather than the class. See https://github.com/Pylons/waitress/pull/1 .

0.8 (2012-01-31)


  • Support the WSGI wsgi.file_wrapper protocol as per http://www.python.org/dev/peps/pep-0333/#optional-platform-specific-file-handling. Here’s a usage example:

    import os
    here = os.path.dirname(os.path.abspath(__file__))
    def myapp(environ, start_response):
        f = open(os.path.join(here, 'myphoto.jpg'), 'rb')
        headers = [('Content-Type', 'image/jpeg')]
            '200 OK',
        return environ['wsgi.file_wrapper'](f, 32768)

    The signature of the file wrapper constructor is (filelike_object, block_size). Both arguments must be passed as positional (not keyword) arguments. The result of creating a file wrapper should be returned as the app_iter from a WSGI application.

    The object passed as filelike_object to the wrapper must be a file-like object which supports at least the read() method, and the read() method must support an optional size hint argument. It should support the seek() and tell() methods. If it does not, normal iteration over the filelike object using the provided block_size is used (and copying is done, negating any benefit of the file wrapper). It should support a close() method.

    The specified block_size argument to the file wrapper constructor will be used only when the filelike_object doesn’t support seek and/or tell methods. Waitress needs to use normal iteration to serve the file in this degenerate case (as per the WSGI spec), and this block size will be used as the iteration chunk size. The block_size argument is optional; if it is not passed, a default value``32768`` is used.

    Waitress will set a Content-Length header on the behalf of an application when a file wrapper with a sufficiently filelike object is used if the application hasn’t already set one.

    The machinery which handles a file wrapper currently doesn’t do anything particularly special using fancy system calls (it doesn’t use sendfile for example); using it currently just prevents the system from needing to copy data to a temporary buffer in order to send it to the client. No copying of data is done when a WSGI app returns a file wrapper that wraps a sufficiently filelike object. It may do something fancier in the future.

0.7 (2012-01-11)


  • Default send_bytes value is now 18000 instead of 9000. The larger default value prevents asyncore from needing to execute select so many times to serve large files, speeding up file serving by about 15%-20% or so. This is probably only an optimization for LAN communications, and could slow things down across a WAN (due to higher TCP overhead), but we’re likely to be behind a reverse proxy on a LAN anyway if in production.
  • Added an (undocumented) profiling feature to the serve() command.

0.6.1 (2012-01-08)

Bug Fixes

  • Remove performance-sapping call to pull_trigger in the channel’s write_soon method added mistakenly in 0.6.

0.6 (2012-01-07)

Bug Fixes

  • A logic error prevented the internal outbuf buffer of a channel from being flushed when the client could not accept the entire contents of the output buffer in a single succession of socket.send calls when the channel was in a “pending close” state. The socket in such a case would be closed prematurely, sometimes resulting in partially delivered content. This was discovered by a user using waitress behind an Nginx reverse proxy, which apparently is not always ready to receive data. The symptom was that he received “half” of a large CSS file (110K) while serving content via waitress behind the proxy.

0.5 (2012-01-03)

Bug Fixes

  • Fix PATH_INFO encoding/decoding on Python 3 (as per PEP 3333, tunnel bytes-in-unicode-as-latin-1-after-unquoting).

0.4 (2012-01-02)


  • Added “design” document to docs.

Bug Fixes

  • Set default connection_limit back to 100 for benefit of maximal platform compatibility.
  • Normalize setting of last_activity during send.
  • Minor resource cleanups during tests.
  • Channel timeout cleanup was broken.

0.3 (2012-01-02)


  • Dont hang a thread up trying to send data to slow clients.
  • Use self.logger to log socket errors instead of self.log_info (normalize).
  • Remove pointless handle_error method from channel.
  • Queue requests instead of tasks in a channel.

Bug Fixes

  • Expect: 100-continue responses were broken.

0.2 (2011-12-31)

Bug Fixes

  • Set up logging by calling logging.basicConfig() when serve is called (show tracebacks and other warnings to console by default).
  • Disallow WSGI applications to set “hop-by-hop” headers (Connection, Transfer-Encoding, etc).
  • Don’t treat 304 status responses specially in HTTP/1.1 mode.
  • Remove out of date interfaces.py file.
  • Normalize logging (all output is now sent to the waitress logger rather than in degenerate cases some output being sent directly to stderr).


  • Support HTTP/1.1 Transfer-Encoding: chunked responses.
  • Slightly better docs about logging.

0.1 (2011-12-30)

  • Initial release.

Known Issues

  • Does not support SSL natively.

Support and Development

The Pylons Project web site is the main online source of Waitress support and development information.

To report bugs, use the issue tracker.

If you’ve got questions that aren’t answered by this documentation, contact the Pylons-devel maillist or join the #pyramid IRC channel.

Browse and check out tagged and trunk versions of Waitress via the Waitress GitHub repository. To check out the trunk via git, use this command:

git clone git@github.com:Pylons/waitress.git

To find out how to become a contributor to Waitress, please see the contributor’s section of the documentation.


At the time of the release of Waitress, there are already many pure-Python WSGI servers. Why would we need another?

Waitress is meant to be useful to web framework authors who require broad platform support. It’s neither the fastest nor the fanciest WSGI server available but using it helps eliminate the N-by-M documentation burden (e.g. production vs. deployment, Windows vs. Unix, Python 3 vs. Python 2, PyPy vs. CPython) and resulting user confusion imposed by spotty platform support of the current (2012-ish) crop of WSGI servers. For example, gunicorn is great, but doesn’t run on Windows. paste.httpserver is perfectly serviceable, but doesn’t run under Python 3 and has no dedicated tests suite that would allow someone who did a Python 3 port to know it worked after a port was completed. wsgiref works fine under most any Python, but it’s a little slow and it’s not recommended for production use as it’s single-threaded and has not been audited for security issues.

At the time of this writing, some existing WSGI servers already claim wide platform support and have serviceable test suites. The CherryPy WSGI server, for example, targets Python 2 and Python 3 and it can run on UNIX or Windows. However, it is not distributed separately from its eponymous web framework, and requiring a non-CherryPy web framework to depend on the CherryPy web framework distribution simply for its server component is awkward. The test suite of the CherryPy server also depends on the CherryPy web framework, so even if we forked its server component into a separate distribution, we would have still needed to backfill for all of its tests. The CherryPy team has started work on Cheroot, which should solve this problem, however.

Waitress is a fork of the WSGI-related components which existed in zope.server. zope.server had passable framework-independent test coverage out of the box, and a good bit more coverage was added during the fork. zope.server has existed in one form or another since about 2001, and has seen production usage since then, so Waitress is not exactly “another” server, it’s more a repackaging of an old one that was already known to work fairly well.