Settings

Use the following options to configure Uvicorn, when running from the command line.

Configuration Methods

There are three ways to configure Uvicorn:

1. Command Line: Use command line options when running Uvicorn directly.

   uvicorn main:app --host 0.0.0.0 --port 8000
   

2. Programmatic: Use keyword arguments when running programmatically with uvicorn.run().

   uvicorn.run("main:app", host="0.0.0.0", port=8000)
   

   Note

   When using reload=True or workers=NUM, you should put uvicorn.run into an if __name__ == '__main__' clause in the main module.

3. Environment Variables: Use environment variables with the prefix UVICORN_.

   export UVICORN_HOST="0.0.0.0"
   export UVICORN_PORT="8000"
   uvicorn main:app
   

CLI options and the arguments for uvicorn.run() take precedence over environment variables.

Also note that UVICORN_* prefixed settings cannot be used from within an environment configuration file. Using an environment configuration file with the --env-file flag is intended for configuring the ASGI application that uvicorn runs, rather than configuring uvicorn itself.

Application

• APP - The ASGI application to run, in the format "<module>:<attribute>".
• --factory - Treat APP as an application factory, i.e. a () -> <ASGI app> callable.
• --app-dir <path> - Look for APP in the specified directory by adding it to the PYTHONPATH. Default: Current working directory.

Socket Binding

• --host <str> - Bind socket to this host. Use --host 0.0.0.0 to make the application available on your local network. IPv6 addresses are supported, for example: --host '::'. Default: '127.0.0.1'.
• --port <int> - Bind to a socket with this port. If set to 0, an available port will be picked. Default: 8000.
• --uds <path> - Bind to a UNIX domain socket, for example --uds /tmp/uvicorn.sock. Useful if you want to run Uvicorn behind a reverse proxy.
• --fd <int> - Bind to socket from this file descriptor. Useful if you want to run Uvicorn within a process manager.

Development

• --reload - Enable auto-reload. Uvicorn supports two versions of auto-reloading behavior enabled by this option. Default: False.
• --reload-dir <path> - Specify which directories to watch for python file changes. May be used multiple times. If unused, then by default the whole current directory will be watched. If you are running programmatically use reload_dirs=[] and pass a list of strings.
• --reload-delay <float> - Delay between previous and next check if application needs to be reloaded. Default: 0.25.

Reloading without watchfiles

If Uvicorn cannot load watchfiles at runtime, it will periodically look for changes in modification times to all *.py files (and only *.py files) inside of its monitored directories. See the --reload-dir option. Specifying other file extensions is not supported unless watchfiles is installed. See the --reload-include and --reload-exclude options for details.

Reloading with watchfiles

For more nuanced control over which file modifications trigger reloads, install uvicorn[standard], which includes watchfiles as a dependency. Alternatively, install watchfiles where Uvicorn can see it.

Using Uvicorn with watchfiles will enable the following options (which are otherwise ignored):

• --reload-include <glob-pattern> - Specify a glob pattern to match files or directories which will be watched. May be used multiple times. By default the following patterns are included: *.py. These defaults can be overwritten by including them in --reload-exclude.
• --reload-exclude <glob-pattern> - Specify a glob pattern to match files or directories which will excluded from watching. May be used multiple times. By default the following patterns are excluded: .*, .py[cod], .sw.*, ~*. These defaults can be overwritten by including them in --reload-include.

Tip

When using Uvicorn through WSL, you might have to set the WATCHFILES_FORCE_POLLING environment variable, for file changes to trigger a reload. See watchfiles documentation for further details.

Production

• --workers <int> - Number of worker processes. Defaults to the $WEB_CONCURRENCY environment variable if available, or 1. Not valid with --reload.
• --env-file <path> - Environment configuration file for the ASGI application. Default: None.

Note

The --reload and --workers arguments are mutually exclusive. You cannot use both at the same time.

Logging

• --log-config <path> - Logging configuration file. Options: dictConfig() formats: .json, .yaml. Any other format will be processed with fileConfig(). Set the formatters.default.use_colors and formatters.access.use_colors values to override the auto-detected behavior.
  • If you wish to use a YAML file for your logging config, you will need to include PyYAML as a dependency for your project or install uvicorn with the [standard] optional extras.
• --log-level <str> - Set the log level. Options: 'critical', 'error', 'warning', 'info', 'debug', 'trace'. Default: 'info'.
• --no-access-log - Disable access log only, without changing log level.
• --use-colors / --no-use-colors - Enable / disable colorized formatting of the log records. If not set, colors will be auto-detected. This option is ignored if the --log-config CLI option is used.

Implementation

• --loop <str> - Set the event loop implementation. The uvloop implementation provides greater performance, but is not compatible with Windows or PyPy. Options: 'auto', 'asyncio', 'uvloop'. Default: 'auto'.
• --http <str> - Set the HTTP protocol implementation. The httptools implementation provides greater performance, but it not compatible with PyPy. Options: 'auto', 'h11', 'httptools'. Default: 'auto'.
• --ws <str> - Set the WebSockets protocol implementation. Either of the websockets and wsproto packages are supported. Use 'none' to ignore all websocket requests. Options: 'auto', 'none', 'websockets', 'wsproto'. Default: 'auto'.
• --ws-max-size <int> - Set the WebSockets max message size, in bytes. Only available with the websockets protocol. Default: 16777216 (16 MB).
• --ws-max-queue <int> - Set the maximum length of the WebSocket incoming message queue. Only available with the websockets protocol. Default: 32.
• --ws-ping-interval <float> - Set the WebSockets ping interval, in seconds. Only available with the websockets protocol. Default: 20.0.
• --ws-ping-timeout <float> - Set the WebSockets ping timeout, in seconds. Only available with the websockets protocol. Default: 20.0.
• --ws-per-message-deflate <bool> - Enable/disable WebSocket per-message-deflate compression. Only available with the websockets protocol. Default: True.
• --lifespan <str> - Set the Lifespan protocol implementation. Options: 'auto', 'on', 'off'. Default: 'auto'.
• --h11-max-incomplete-event-size <int> - Set the maximum number of bytes to buffer of an incomplete event. Only available for h11 HTTP protocol implementation. Default: 16384 (16 KB).

Application Interface

• --interface <str> - Select ASGI3, ASGI2, or WSGI as the application interface. Note that WSGI mode always disables WebSocket support, as it is not supported by the WSGI interface. Options: 'auto', 'asgi3', 'asgi2', 'wsgi'. Default: 'auto'.

Warning

Uvicorn's native WSGI implementation is deprecated, you should switch to a2wsgi (pip install a2wsgi).

HTTP

• --root-path <str> - Set the ASGI root_path for applications submounted below a given URL path. Default: "".
• --proxy-headers / --no-proxy-headers - Enable/Disable X-Forwarded-Proto, X-Forwarded-For to populate remote address info. Defaults to enabled, but is restricted to only trusting connecting IPs in the forwarded-allow-ips configuration.
• --forwarded-allow-ips <comma-separated-list> - Comma separated list of IP Addresses, IP Networks, or literals (e.g. UNIX Socket path) to trust with proxy headers. Defaults to the $FORWARDED_ALLOW_IPS environment variable if available, or '127.0.0.1'. The literal '*' means trust everything.
• --server-header / --no-server-header - Enable/Disable default Server header. Default: True.
• --date-header / --no-date-header - Enable/Disable default Date header. Default: True.
• --header <name:value> - Specify custom default HTTP response headers as a Name:Value pair. May be used multiple times.

Note

The --no-date-header flag doesn't have effect on the websockets implementation.

HTTPS

The SSL context can be configured with the following options:

• --ssl-keyfile <path> - The SSL key file.
• --ssl-keyfile-password <str> - The password to decrypt the ssl key.
• --ssl-certfile <path> - The SSL certificate file.
• --ssl-version <int> - The SSL version to use. Default: ssl.PROTOCOL_TLS_SERVER.
• --ssl-cert-reqs <int> - Whether client certificate is required. Default: ssl.CERT_NONE.
• --ssl-ca-certs <str> - The CA certificates file.
• --ssl-ciphers <str> - The ciphers to use. Default: "TLSv1".

To understand more about the SSL context options, please refer to the Python documentation.

Resource Limits

• --limit-concurrency <int> - Maximum number of concurrent connections or tasks to allow, before issuing HTTP 503 responses. Useful for ensuring known memory usage patterns even under over-resourced loads.
• --limit-max-requests <int> - Maximum number of requests to service before terminating the process. Useful when running together with a process manager, for preventing memory leaks from impacting long-running processes.
• --backlog <int> - Maximum number of connections to hold in backlog. Relevant for heavy incoming traffic. Default: 2048.

Timeouts

• --timeout-keep-alive <int> - Close Keep-Alive connections if no new data is received within this timeout. Default: 5.
• --timeout-graceful-shutdown <int> - Maximum number of seconds to wait for graceful shutdown. After this timeout, the server will start terminating requests.