Dancer2::Config - Configure Dancer2 to suit your needs


version 1.1.0


The Dancer2 configuration (as implemented by Dancer2::Core::Role::ConfigReader) handles reading and changing the configuration of your Dancer2 apps. This document describes how to manipulate Dancer2's configuration settings (through code or by file), and to document the various settings that are available in Dancer2.


You can change a setting with the keyword set:

use Dancer2;

# changing default settings
set port         => 8080;
set content_type => 'text/plain';
set startup_info => 0;


There's nothing wrong with using set to configure your application. In fact you might have some great reasons for doing so. For greater flexibility, ease of deployment, etc., you should also consider extracting those settings into a configuration file.

Configuration file path and file names

Dancer2 will first look for the file config.EXT (where EXT is the type of configuration file you are using; e.g. ini or json or yml) in the root directory of your application. This is considered your global Dancer2 config file. If you do not care to have separate settings for production and development environments (not a recommended practice!), then this file is all you need.

Next, Dancer2 will look for a file called config_local.EXT. This file is typically useful for deployment-specific configuration that should not be checked into source control. For instance, database credentials could be stored in this file. Any settings in this file are merged into the existing configuration such that those with the same name in your local configuration file will take precedence over those settings in the global file.

Next, Dancer2 will look in the environments directory for a configuration file specific to the platform you are deploying to (production.EXT or development.EXT, for example). Again, the configuration from the environment is merged with the existing configuration with the deployment config taking precedence.

Finally, Dancer2 will look in the environments directory for a local configuration for the specific platform you are deploying to (e.g. production_local.EXT or development_local.EXT) The configuration in this file is merged as before.

Much like config_local.EXT, this file would be useful for environment- specific configuration that would not be checked into source control. For instance, when developing an application that talks to multiple services, each developer could have their own URLs to those services stored within their environments/development_local.yaml file.

Note, if there is no config.EXT, Dancer2 will not look for a config_local.EXT. The same is true for the local environment configuration.

Supported configuration file formats

Dancer2 supports any configuration file format that is supported by Config::Any. At the time of this writing, that includes YAML (.yml and .yaml), JSON (.jsn and .json), INI (.ini), Apache-style configurations (.cnf and .conf), XML (.xml), and Perl-style hashes (.pl and .perl).

Dancer2 iterates over these file extensions in the order provided by Config::Any and loads any config files that it finds with later configuration information overriding earlier config information. To restrict which file extension Dancer2 looks for, you may set the DANCER_CONFIG_EXT envinroment variable to a specific extension and Dancer2 will only look for config files with that extension.

Make sure you pick the appropriate extension for your configuration file name, as Dancer2 guesses the type of format based on the file extension.

Sample configuration files

Note: Not all possibilities are covered here, only the most common options.

If you prefer YAML, a sample YAML based config file might look like this:

appname: "Hello"
charset: "UTF-8"
auto_page: 1

session: "YAML"
serializer: "JSON"

      dsn: dbi:SQLite:db/mydata.db
      schema_class: Hello::Schema

If JSON is more your thing, your file might look more like this:

    "appname": "Hello",
    "charset": "UTF-8",
    "auto_page": "1",
    "session": "YAML",
    "serializer": "JSON",
    "plugins": {
        "DBIC": {
            "default": {
                "dsn": "dbi:SQLite:db/mydata.db",
                "schema_class": "Hello::Schema"

If you like Apache configuration files, try something similar to:

appname = Hello
charset = UTF-8
auto_page = 1
session = YAML
serializer = JSON
            dsn = dbi =SQLite =db/mydata.db
            schema_class = Hello = =Schema

INI-style files are deliberately simplistic and not recommended for use in your Dancer2 applications.


Run mode and listening interface/port

host (string)

The IP address that the Dancer2 app should bind to. Default is, i.e. bind to all available interfaces.

port (int)

The port Dancer2 will listen to.

Default value is 3000. This setting can be changed on the command-line with the --port switch.

behind_proxy (boolean)

If set to true, Dancer2 will look to X-Forwarded-Protocol and X-Forwarded-host when constructing URLs (for example, when using redirect or host). This is useful if your application is behind a proxy.

Note: If either of these are missing, the values of the proxy server will be used instead. For example, if the client sends a HTTP/1.0 request to a proxy that is hosted locally, then host will return the value "localhost". In a similar vein, if the client makes a secure connection to the proxy, but the proxy does not pass X-Forwarded-Protocol, then base will return "http://...". For these reasons, it is recommended that the values are hard-configured in the proxy if possible. For Apache this would be:

RequestHeader set X_FORWARDED_PROTO "https"
RequestHeader set X_FORWARDED_HOST ""

no_default_middleware (boolean)

If set to true, your Dancer2 application will NOT be wrapped with the default PSGI middleware. The default middleware wrappers are:

Content type / character set

content_type (string)

The default content type of outgoing content. Default value is 'text/html'.

charset (string)

This setting has multiple effects:

Default value is empty which means don't do anything. HTTP responses without charset will be interpreted as ISO-8859-1 by most clients.

You can cancel any charset processing by specifying your own charset in Content-Type header or by ensuring that response body leaves your handler without Unicode flag set (by encoding it into some 8bit charset, for example).

Also, since automatically serialized JSON responses have application/json Content-Type, you should always encode them by hand.

default_mime_type (string)

Dancer2's Dancer2::Core::MIME module uses application/data as a default mime type. This setting lets the user change it. For example, if you have a lot of files being served in the public folder that do not have an extension, and are text files, set the default_mime_type to text/plain.

Serializing responses

serializer (string)

When writing a webservice, data serialization/deserialization is a common issue to deal with. Dancer2 can automatically handle that for you, via a serializer.

Available serializer engines

The following serializers are available, be aware they dynamically depend on Perl modules you may not have on your system.

Serializer engine

The serializer can be configured in a separate engines section, like so:

serializer: "JSON"

      pretty: 1

See documentation for a particular serializer for supported options.

File / directory locations

environment (string)

This is the name of the environment that should be used. Standard Dancer2 applications have a environments folder with specific configuration files for different environments (usually development and production environments). They specify different kind of error reporting, deployment details, etc. These files are read after the generic config.yml configuration file.

appdir (directory)

This is the path where your application will live. It's where Dancer2 will look by default for your config files, templates and static content.

It is typically set by use Dancer2 to use the same directory as your script.

public_dir (directory)

This is the directory, where static files are stored. Any existing file in that directory will be served as a static file, before matching any route.

See also static_handler.

Default: $appdir/public.

static_handler (boolean)

This setting have to be declared and set to true if you modify standard public_dir location.

Default: true if $ENV{DANCER_PUBLIC} is set or public_dir is set to $appdir/public.

views (directory)

This is the directory where your templates and layouts live. It's the "view" part of MVC (model, view, controller).

Default: $appdir/views.

Templating & layouts


Allows you to configure which template engine should be used. For instance, to use Template Toolkit, add the following to config.yml:

template: template_toolkit

layout (string)

The name of the layout to use when rendering view. Dancer2 will look for a matching template in the directory $views/layouts.

Your can override the default layout using the third argument of the template keyword. Check Dancer2 manpage for details.

layout_dir (string)

A relative path where the layouts reside inside the views directory.

layout_dir: actual_layouts

Default: layouts.

Logging, debugging and error handling

startup_info (boolean)

If set to true, prints a banner at the server start with information such as versions and the environment (or "dancefloor").

Conforms to the environment variable DANCER_STARTUP_INFO.

traces (boolean)

If set to true, Dancer2 will display full stack traces when a warning or a die occurs. (Internally sets Carp::Verbose). Default to false.

no_server_tokens (boolean)

If set to true, Dancer2 will not add an "X-Powered-By" header and also append the Dancer2 version to the "Server" header. Default to false - adding.

You can also use the environment variable DANCER_NO_SERVER_TOKENS.

logger (enum)

Select which logger to use. For example, to write to log files with Dancer2::Logger::File:

logger: File

Or to direct log messages to the console from which you started your Dancer2 app with Dancer2::Logger::Console:

logger: Console

Loggers are configured with a corresponding "Logger engine" section, as shown below.

session (enum)

This setting lets you enable a session engine for your web application. By default, sessions are disabled in Dancer2, you must choose a session engine to use them.

Sessions are configured with a corresponding "Session engine" section, as shown below.

show_errors (boolean)

Deprecated configuration.

Use show_stacktrace described below instead.

show_stacktrace (boolean)

If set to true, Dancer2 will render a detailed debug screen whenever an error is caught. If set to false, Dancer2 will render the default error page, using $public/$error_code.html if it exists, $views/$ or the template specified by the error_template setting.

The error screen attempts to sanitise sensitive looking information (passwords / card numbers in the request, etc) but you still should not have show_stacktrace enabled whilst in production, as there is still a risk of divulging details.

error_template (template path)

This setting lets you specify a template to be used in case of runtime error. At the present moment the template (as well as $views/$ templates) can use four variables:


The error title.


The error specific content (if any).


The HTTP status code throwing that error.


The stringified exception (e.g. $@) if any.

Keep in mind that 'content' and 'exception' can vary depending on the problem.

For example:

A 404 has an empty 'exception' and 'content' contains the URI that was not found. Unless you do the 404 yourself via send_error("You chose ... poorly!", 404);, then 'content' is 'You chose ... poorly!'.

A 500 because of, say, dividing 0 by 0 will have an empty 'content' and 'exception like 'Illegal division by zero at ...'.

A 401 from send_error("You can not know the secret until you sign in grasshopper!", 401); will have an empty 'exception' and 'content' will contain 'You can not know the secret until you sign in grasshopper!'.

Logger engine

The logger must be configured in a separate engines section, like so:

logger: Console

      log_level: core

All loggers support the configuration options below. See documentation for a particular logger for other supported options.


This option tells which log messages should be actually logged. Possible values are core, info, debug, warning or error.

core : all messages are logged, including some from Dancer2 itself
debug : all messages are logged
info : only info, warning and error messages are logged
warning : only warning and error messages are logged
error : only error messages are logged

During development, you'll probably want to use debug to see your own debug messages, and core if you need to see what Dancer2 is doing. In production, you'll likely want error or warning only, for less-chatty logs.

Session engine

The session engine is configured in the engines section.

session: Simple

      cookie_name: dance.set
      cookie_duration: '24 hours'
      cookie_same_site: Lax
      is_secure: 1
      is_http_only: 1

See Dancer2::Core::Role::SessionFactory for more detailed documentation for these options, or the particular session engine for other supported options.

The name of the cookie to store the session ID in. Defaults to dancer.session. This can be overridden by certain session engines.

The domain of the cookie. By default there is no domain defined for the cookie.

The path of the cookie. By default there is no path defined for the cookie.

The session expiry time in seconds, or as e.g. "2 hours" (see "expires" in Dancer2::Core::Cookie. By default, there is no specific expiry time.

Restricts the session cookie to a first-party or same-site context. Valid values are Strict, Lax, or None.

Refer to RFC6265bis for further details regarding same-site context.


The user's session ID is stored in a cookie. If the is_secure setting is set to a true value, the cookie will be marked as secure, meaning it should only be sent over HTTPS connections.


This setting defaults to 1 and instructs the session cookie to be created with the HttpOnly option active, meaning that JavaScript will not be able to access to its value.

auto_page (boolean)

For simple pages where you're not doing anything dynamic, but still want to use the template engine to provide headers etc, you can use the auto_page feature to avoid the need to create a route for each page.

With auto_page enabled, if the requested path does not match any specific route, Dancer2 will check in the views directory for a matching template, and use it to satisfy the request if found.

Simply enable auto_page in your config:

auto_page: 1

Then, if you request /foo/bar, Dancer2 will look in the views dir for /foo/

Dancer2 will honor your before_template_render code, and all default variables. They will be accessible and interpolated on automatic served pages.


For complex applications that require extended DSL keywords or other functionality the DSL class used can be specified at import time or in the config settings.

dsl_class: 'My::DSL'

This is the same as specifying

use Dancer2 dsl => 'My::DSL'

in your module. dsl_class defaults to Dancer2::Core::DSL if not specified

Environment variables


Sets the configuration directory.

This correlates to the confdir config option.


Sets the environment directory.

This correlates to the envdir config option.


Sets the given environment. This can be overridden by DANCER_ENVIRONMENT.


Sets the given environment. This takes higher precedence over PLACK_ENV.

If neither PLACK_ENV or DANCER_ENVIRONMENT is set, the environment defaults to development.


The DANCER_APPHANDLER configuration controls what the dance keyword does.

If is set to PSGI (which will automatically be set if PLACK_ENV is set), dance will return the PSGI application coderef.

Otherwise (which is the default is - Standalone), it runs the Plack standalone server with the application.


Sets the port which will be used by the development server (if not run by plackup).


Sets the host the development server will be used by the development server (if not run by plackup).

Note: this might change in the future.


Controls whether to display start up info.


Controls whether to display the server tokens.


Sets the public directory location.


Sets the tracing flag which sets Carp's $Verbose flag.


Sets the views (templates) directory.


Sets the logger engine.


Sets the default charset.


Sets the default content type.

If not set, defaults to text/html.




Dancer Core Developers


This software is copyright (c) 2023 by Alexis Sukrieh.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.