Dancer2::Manual::Keywords - Dancer2 DSL Keywords


version 0.301004


Dancer2 provides you with a DSL (Domain-Specific Language) which makes implementing your web application trivial.

For example, take the following example:

    use Dancer2;

    get '/hello/:name' => sub {
        my $name = route_parameters->get('name');

get and route_parameters are keywords provided by Dancer2.

This document lists all keywords provided by Dancer2. It does not cover additional keywords which may be provided by loaded plugins; see the documentation for plugins you use to see which additional keywords they make available to you.


Defines a route for multiple HTTP methods at once:

    any ['get', 'post'] => '/myaction' => sub {
        # code

Or even, a route handler that would match any HTTP methods:

    any '/myaction' => sub {
        # code


Returns an instance of the app. App is a Dancer2::Core::App.


Returns a Hash::MultiValue object from the body parameters.

    post '/' => sub {
        my $last_name = body_parameters->get('name');
        my @all_names = body_parameters->get_all('name');


Returns a reference to a copy of %+, if there are named captures in the route's regular expression.

Named captures are a feature of Perl 5.10, and are not supported in earlier versions:

    get qr{
        / (?<object> user   | ticket | comment )
        / (?<action> delete | find )
        / (?<id> \d+ )
    , sub {
        my $value_for = captures;
        "i don't want to $value_for->{action} " . 
            "the $value_for->{object} $value_for->{id} !"

Accesses a cookie value (or sets it). Note that this method will eventually be preferred over set_cookie.

    cookie lang => "fr-FR";              # set a cookie and return its value
    cookie lang => "fr-FR", expires => "2 hours";   # extra cookie info
    cookie "lang"                        # return a cookie value

If your cookie value is a key/value URI string, like


cookie will only return the first part (token=ABC) if called in scalar context. Use list context to fetch them all:

    my @values = cookie "name";


Accesses cookies values, it returns a hashref of Dancer2::Core::Cookie objects:

    get '/some_action' => sub {
        my $cookie = cookies->{name};
        return $cookie->value;

In case you have stored something other than a scalar in your cookie:

    get '/some_action' => sub {
        my $cookie = cookies->{oauth};
        my %values = $cookie->value;
        return ($values{token}, $values{token_secret});


Accesses the configuration of the application:

    get '/appname' => sub {
        return "This is " . config->{appname};


Sets the content for the response. This only works within a delayed response.

This will crash:

    get '/' => sub {
        content 'Hello, world!';

But this will work just fine:

    get '/' => sub {
        delayed {
            content 'Hello, world!';


Sets the content-type rendered, for the current route handler:

    get '/cat/:txtfile' => sub {
        content_type 'text/plain';

        # here we can dump the contents of route_parameters->get('txtfile')

You can use abbreviations for content types. For instance:

    get '/svg/:id' => sub {
        content_type 'svg';

        # here we can dump the image with id route_parameters->get('id')

Note that if you want to change the default content-type for every route, it is easier to change the content_type setting instead.


Deprecated. Use app instead.


Alias for the start keyword. to_app is preferable.


Returns the app object. See app.


Returns the version of Dancer. If you need the major version, do something like:


or (better), call dancer_major_version.


Returns the major version of Dancer.


Logs a message of debug level:

    debug "This is a debug message";

See Dancer2::Core::Role::Logger for details on how to configure where log messages go.

decode_json ($string)

Deserializes a JSON structure from an UTF-8 binary string.


Defines a route for HTTP DELETE requests to the given URL:

    del '/resource' => sub { ... };


Stream a response asynchronously. For more information, please see "Delayed responses (Async/Streaming)" in Dancer2::Manual, or this article in the 2020 Dancer Advent Calendar.


Returns the dirname of the path given:

    my $dir = dirname($some_path);


Close the streaming connection. Can only be called within a streaming response callback.


Allows access to the DSL within your plugin/application. Is an instance of Dancer2::Core::DSL.

encode_json ($structure)

Serializes a structure to a UTF-8 binary JSON string.

Calling this function will not trigger the serialization's hooks.


Given a namespace, returns the current engine object

    my $template_engine = engine 'template';
    my $html = $template_engine->apply_renderer(...);


Logs a message of error level:

    error "This is an error message";

See Dancer2::Core::Role::Logger for details on how to configure where log messages go.


Constant that returns a false value (0).


Flush headers when streaming a response. Necessary when content is called multiple times.


Runs an "internal redirect" of the current route to another route. More formally; when forward is executed, the current dispatch of the route is aborted, the request is modified (altering query params or request method), and the modified request following a new route is dispatched again. Any remaining code (route and hooks) from the current dispatch will never be run and the modified route's dispatch will execute hooks for the new route normally.

It effectively lets you chain routes together in a clean manner.

    get '/demo/articles/:article_id' => sub {

        # you'll have to implement this next sub yourself :)

        forward "/articles/" . route_parameters->get('article_id');

In the above example, the users that reach /demo/articles/30 will actually reach /articles/30 but we've changed the database to demo before.

This is pretty cool because it lets us retain our paths and offer a demo database by merely going to /demo/....

You'll notice that in the example we didn't indicate whether it was GET or POST. That is because forward chains the same type of route the user reached. If it was a GET, it will remain a GET (but if you do need to change the method, you can do so; read on below for details.)

Also notice that forward only redirects to a new route. It does not redirect the requests involving static files. This is because static files are handled before Dancer2 tries to match the request to a route - static files take higher precedence.

This means that you will not be able to forward to a static file. If you wish to do so, you have two options: either redirect (asking the browser to make another request, but to a file path instead) or use send_file to provide a file.

WARNING: Any code after a forward is ignored, until the end of the route. It's not necessary to use return with forward anymore.

    get '/foo/:article_id' => sub {
        if ($condition) {
            forward "/articles/" . route_parameters->get('article_id');
            # The following code WILL NOT BE executed


Note that forward doesn't parse GET arguments. So, you can't use something like:

    forward '/home?authorized=1';

But forward supports an optional hashref with parameters to be added to the actual parameters:

    forward '/home', { authorized => 1 };

Finally, you can add some more options to the forward method, in a third argument, also as a hashref. That option is currently only used to change the method of your request. Use with caution.

    forward '/home', { auth => 1 }, { method => 'POST' };

from_dumper ($structure)

Deserializes a Data::Dumper structure.

from_json ($string, \%options)

Deserializes a JSON structure from a string. You should probably use decode_json which expects a UTF-8 encoded binary string and handles decoding it for you.

from_yaml ($structure)

Deserializes a YAML structure.


Defines a route for HTTP GET requests to the given path:

    get '/' => sub {
        return "Hello world";

Note that a route to match HEAD requests is automatically created as well.


Sets a response object with the content given.

When used as a return value from a hook, this breaks the execution flow and renders the response immediately:

    hook before => sub {
        if ($some_condition) {

            # this code is not executed

    get '/' => sub {
        "hello there";

WARNING: Issuing a halt immediately exits the current route, and performs the halt. Thus, any code after a halt is ignored, until the end of the route. Hence, it's not necessary anymore to use return with halt.

Deprecated. Use response_header instead.


Deprecated. Use response_headers instead.


Adds a hook at some position. For example :

  hook before_serializer => sub {
    my $content = shift;

There can be multiple hooks assigned to a given position, and each will be executed in order.

See the HOOKS section for a list of available hooks.


Logs a message of info level:

    info "This is an info message";

See Dancer2::Core::Role::Logger for details on how to configure where log messages go.


Logs messages at the specified level. For example:

    log( debug => "This is a debug message." );


Shortcut to access the instance object of Dancer2::Core::MIME. You should read the Dancer2::Core::MIME documentation for full details, but the most commonly-used methods are summarized below:

    # set a new mime type
    mime->add_type( foo => 'text/foo' );

    # set a mime type alias
    mime->add_alias( f => 'foo' );

    # get mime type for an alias
    my $m = mime->for_name( 'f' );

    # get mime type for a file (based on extension)
    my $m = mime->for_file( "" );

    # get current defined default mime type
    my $d = mime->default;

    # set the default mime type using config.yml
    # or using the set keyword
    set default_mime_type => 'text/plain';


Defines a route for HTTP OPTIONS requests to the given URL:

    options '/resource' => sub { ... };


This method should be called from a route handler. This method is an accessor to the parameters hash table.

   post '/login' => sub {
       my $username = param "user";
       my $password = param "pass";
       # ...

We now recommend using one of the specific keywords for parameters (route_parameters, query_parameters, and body_parameters) instead of params or param.


This method should be called from a route handler. It's an alias for the Dancer2::Core::Request params accessor. It returns a hash (in list context) or a hash reference (in scalar context) to all defined parameters. Check param below to access quickly to a single parameter value.

    post '/login' => sub {
        # get all parameters as a single hash
        my %all_parameters = params;

        // request all parmameters from a specific source: body, query, route
        my %body_parameters  = params('body');
        my %route_parameters = params('route');
        my %query_parameters = params('query');

        # any $source that is not body, query, or route generates an exception
        params('fake_source'); // Unknown source params "fake_source"

We now recommend using one of the specific keywords for parameters (route_parameters, query_parameters, and body_parameters) instead of params or param.


This method should be called from a route handler. Tells Dancer2 to pass the processing of the request to the next matching route.

WARNING: Issuing a pass immediately exits the current route, and performs the pass. Thus, any code after a pass is ignored, until the end of the route. Hence, it's not necessary anymore to use return with pass.

    get '/some/route' => sub {
        if (...) {
            # we want to let the next matching route handler process this one

            # this code will be ignored

WARNING: You cannot set the content before passing and have it remain, even if you use the content keyword or set it directly in the response object.


Defines a route for HTTP PATCH requests to the given URL:

    patch '/resource' => sub { ... };

(PATCH is a relatively new and not-yet-common HTTP verb, which is intended to work as a "partial-PUT", transferring just the changes; please see RFC5789 for further details.)


Concatenates multiple paths together, without worrying about the underlying operating system:

    my $path = path(dirname($0), 'lib', '');

It also normalizes (cleans) the path aesthetically. It does not verify whether the path exists, though.


Defines a route for HTTP POST requests to the given URL:

    post '/' => sub {
        return "Hello world";


Defines a prefix for each route handler, like this:

    prefix '/home';

From here, any route handler is defined to /home/*:

    get '/page1' => sub {}; # will match '/home/page1'

You can unset the prefix value:

    prefix undef;
    get '/page1' => sub {}; # will match /page1

For a safer alternative you can use lexical prefix like this:

    prefix '/home' => sub {
        ## Prefix is set to '/home' here

        get ...;
        get ...;
    ## prefix reset to the previous version here

This makes it possible to nest prefixes:

   prefix '/home' => sub {
       ## some routes

      prefix '/private' => sub {
         ## here we are under /home/private...

         ## some more routes
      ## back to /home
   ## back to the root

Notice: Once you have a prefix set, do not add a caret to the regex:

    prefix '/foo';
    get qr{^/bar} => sub { ... } # BAD BAD BAD
    get qr{/bar}  => sub { ... } # Good!


You can introduce code you want to run when your app is loaded, similar to the prepare_app in Plack::Middleware.

    prepare_app {
        my $app = shift;

        ... # do your thing

You should not close over the App instance, since you receive it as a first argument. If you close over it, you will have a memory leak.

    my $app = app();

    prepare_app {
        do_something_with_app($app); # MEMORY LEAK


Provides the same functionality as to_app but uses the deprecated Dispatcher engine. You should use to_app instead.


Deprecated. Use push_response_header instead.


Do the same as response_header, but allow for multiple headers with the same name.

    get '/send/header', sub {
        push_response_header 'x-my-header' => '1';
        push_response_header 'x-my-header' => '2';
        # will result in two headers "x-my-header" in the response


Defines a route for HTTP PUT requests to the given URL:

    put '/resource' => sub { ... };


Returns a Hash::MultiValue object from the request parameters.

    get '/' => sub {
        my $name = query_parameters->get('foo');

    get '/' => sub {
        my @names = query_parameters->get_all('name');


Generates a HTTP redirect (302). You can either redirect to a complete different site or within the application:

    get '/twitter', sub {
        redirect '';
        # Any code after the redirect will not be executed.

WARNING: Issuing a redirect immediately exits the current route. Thus, any code after a redirect is ignored, until the end of the route. Hence, it's not necessary anymore to use return with redirect.

You can also force Dancer to return a specific 300-ish HTTP response code:

    get '/old/:resource', sub {
        redirect '/new/' . route_parameters->get('resource'), 301;


Returns a Dancer2::Core::Request object representing the current request.

See the Dancer2::Core::Request documentation for the methods you can call, for example:

    request->referer;         # value of the HTTP referer header
    request->remote_address;  # user's IP address
    request->user_agent;      # User-Agent header value


Returns the request's body in data form (in case a serializer is set, it will be in deserialized).

This allows us to distinguish between body_parameters, a representation of request parameters (Hash::MultiValue) and other forms of content.


Returns request header(s).

    get '/get/headers' => sub {
        my $xfoo = request_header 'X-Foo';


Returns the current response object, which is of type Dancer2::Core::Route::REQUEST.


Adds a custom header to response:

    get '/send/header', sub {
        response_header 'x-my-header' => 'shazam!';

Note that it will overwrite the old value of the header, if any. To avoid that, see "push_response_header".


Adds custom headers to response:

    get '/send/headers', sub {
        response_headers 'X-Foo' => 'bar', 'X-Bar' => 'foo';


Returns a Hash::MultiValue object from the route parameters.

    # /hello
    get '/:foo' => sub {
        my $foo = route_parameters->get('foo');


Returns the runner singleton. Type is Dancer2::Core::Runner.


Allows the current route handler to return specific content types to the client using either a specified serializer or as html.

Any Dancer2 serializer may be used. The specified serializer class will be loaded if required, or an error generated if the class can not be found. Serializer configuration may be added to your apps engines configuration.

If html is specified, the content will be returned assuming it is HTML with appropriate Content-Type headers and encoded using the apps configured charset (or UTF-8).

    set serializer => 'YAML';
    set template   => 'TemplateToolkit';

    # returns html (not YAML)
    get '/' => sub { send_as html => template '' };

    # return json (not YAML)
    get '/json' => sub {
        send_as JSON => [ some => { data => 'structure' } ];

send_as uses "send_file" to return the content immediately. You may pass any option send_file supports as an extra option. For example:

    # return json with a custom content_type header
    get '/json' => sub {
        send_as JSON => [ some => { data => 'structure' } ],
                { content_type => 'application/json; charset=UTF-8' },

WARNING: Issuing a send_as immediately exits the current route, and performs the send_as. Thus, any code after a send_as is ignored, until the end of the route. Hence, it's not necessary to use return with send_as.

    get '/some/route' => sub {
        if (...) {
            send_as JSON => $some_data;

            # this code will be ignored


Returns a HTTP error. By default the HTTP code returned is 500:

    get '/photo/:id' => sub {
        if (...) {
            send_error("Not allowed", 403);
        } else {
           # return content

WARNING: Issuing a send_error immediately exits the current route, and performs the send_error. Thus, any code after a send_error is ignored, until the end of the route. Hence, it's not necessary anymore to use return with send_error.

    get '/some/route' => sub {
        if (...) {
            # Something bad happened, stop immediately!

            # this code will be ignored


Lets the current route handler send a file to the client. Note that the path of the file must be relative to the public directory unless you use the system_path option (see below).

    get '/download/:file' => sub {
        return send_file(route_parameters->get('file'));

WARNING: Issuing a send_file immediately exits the current route, and performs the send_file. Thus, any code after a send_file is ignored, until the end of the route. Hence, it's not necessary anymore to use return with send_file.

    get '/some/route' => sub {
        if (...) {
            # OK, send her what she wants...

            # this code will be ignored

send_file will use PSGI streaming if the server supports it (most, if not all, do). You can explicitly disable streaming by passing streaming => 0 as an option to send_file.

    get '/download/:file' => sub {
        send_file( route_parameters->get('file'), streaming => 0 );

The content-type will be set depending on the current MIME types definition (see mime if you want to define your own).

If your filename does not have an extension, you are passing in a filehandle, or you need to force a specific mime type, you can pass it to send_file as follows:

    send_file(route_parameters->get('file'), content_type => 'image/png');
    send_file($fh, content_type => 'image/png');

Also, you can use your aliases or file extension names on content_type, like this:

    send_file(route_parameters->get('file'), content_type => 'png');

The encoding of the file or filehandle may be specified by passing both the content_type and charset options. For example:

    send_file($fh, content_type => 'text/csv', charset => 'utf-8' );

For files outside your public folder, you can use the system_path switch. Just bear in mind that its use needs caution as it can be dangerous.

   send_file('/etc/passwd', system_path => 1);

If you have your data in a scalar variable, send_file can be useful as well. Pass a reference to that scalar, and send_file will behave as if there was a file with that contents:

   send_file( \$data, content_type => 'image/png' );

Note that Dancer is unable to guess the content type from the data contents. Therefore you might need to set the content_type properly. For this kind of usage an attribute named filename can be useful. It is used as the Content-Disposition header, to hint the browser about the filename it should use.

   send_file( \$data, content_type => 'image/png'
                      filename     => 'onion.png' );

By default the Content-Disposition header uses the "attachment" type, which triggers a "Save" dialog in some browsers. Supply a content_disposition attribute of "inline" to have the file displayed inline by the browser.


Provides access to all data stored in the user's session (if any).

It can also be used as a setter to store data in the session:

    # getter example
    get '/user' => sub {
        if (session('user')) {
            return "Hello, ".session('user')->name;

    # setter example
    post '/user/login' => sub {
        if ($logged_in) {
            session user => $user;

You may also need to clear a session:

    # destroy session
    get '/logout' => sub {

If you need to fetch the session ID being used for any reason:

    my $id = session->id;


Defines a setting:

    set something => 'value';

You can set more than one value at once:

    set something => 'value', otherthing => 'othervalue';


Returns the value of a given setting:

    setting('something'); # 'value'


Returns the list of captures made from a route handler with a route pattern which includes wildcards:

    get '/file/*.*' => sub {
        my ($file, $extension) = splat;

There is also the extensive splat (A.K.A. "megasplat"), which allows extensive greedier matching, available using two asterisks. The additional path is broken down and returned as an arrayref:

    get '/entry/*/tags/**' => sub {
        my ( $entry_id, $tags ) = splat;
        my @tags = @{$tags};

The splat keyword in the above example for the route /entry/1/tags/one/two would set $entry_id to 1 and $tags to ['one', 'two'].


Starts the application or the standalone server (depending on the deployment choices).

This keyword should be called at the very end of the script, once all routes are defined. At this point, Dancer2 takes over.

to_app is preferable to dancer or start.


Changes the status code provided by an action. By default, an action will produce an HTTP 200 OK status code, meaning everything is OK:

    get '/download/:file' => {
        if (! -f route_parameters->get('file')) {
            status 'not_found';
            return "File does not exist, unable to download";
        # serving the file...

In that example, Dancer will notice that the status has changed, and will render the response accordingly.

The status keyword receives either a numeric status code or its name in lower case, with underscores as a separator for blanks - see the list in "HTTP CODES" in Dancer2::Core::HTTP. As an example, The above call translates to setting the code to 404.


Returns the response of processing the given template with the given parameters (and optional settings), wrapping it in the default or specified layout too, if layouts are in use.

An example of a route handler which returns the result of using template to build a response with the current template engine:

    get '/' => sub {
        return template 'some_view', { token => 'value'};

Note that template simply returns the content, so when you use it in a route handler, if execution of the route handler should stop at that point, make sure you use return to ensure your route handler returns the content.

Since template just returns the result of rendering the template, you can also use it to perform other templating tasks, e.g. generating emails:

    post '/some/route' => sub {
        if (...) {
            email {
                to      => '',
                from    => '',
                subject => 'Hello there',
                msg     => template('emails/foo', { name => body_parameters->get('name') }),

            return template 'message_sent';
        } else {
            return template 'error';

Compatibility notice: template was changed in version 1.3090 to immediately interrupt execution of a route handler and return the content, as it's typically used at the end of a route handler to return content. However, this caused issues for some people who were using template to generate emails etc, rather than accessing the template engine directly, so this change has been reverted in 1.3091.

The first parameter should be a template available in the views directory, the second one (optional) is a hashref of tokens to interpolate, and the third (again optional) is a hashref of options.

For example, to disable the layout for a specific request:

    get '/' => sub {
        template 'index', {}, { layout => undef };

Or to request a specific layout, of course:

    get '/user' => sub {
        template 'user', {}, { layout => 'user' };

Some tokens are automatically added to your template (perl_version, dancer_version, settings, request, vars and, if you have sessions enabled, session). Check Default Template Variables for further details.


Returns the PSGI coderef for the current (and only the current) application.

You can call it as a method on the class or as a DSL:

    my $app = MyApp->to_app;

    # or

    my $app = to_app;

There is a Dancer Advent Calendar article covering this keyword and its usage further.

to_dumper ($structure)

Serializes a structure with Data::Dumper.

Calling this function will not trigger the serialization's hooks.

to_json ($structure, \%options)

Serializes a structure to JSON. You should probably use encode_json instead which handles encoding the result for you.

to_yaml ($structure)

Serializes a structure to YAML.

Calling this function will not trigger the serialization's hooks.


Constant that returns a true value (1).


Provides access to file uploads. Any uploaded file is accessible as a Dancer2::Core::Request::Upload object. You can access all parsed uploads via:

    post '/some/route' => sub {
        my $file = upload('file_input_foo');
        # $file is a Dancer2::Core::Request::Upload object

If you named multiple inputs of type "file" with the same name, the upload keyword would return an Array of Dancer2::Core::Request::Upload objects:

    post '/some/route' => sub {
        my ($file1, $file2) = upload('files_input');
        # $file1 and $file2 are Dancer2::Core::Request::Upload objects

You can also access the raw hashref of parsed uploads via the current request object:

    post '/some/route' => sub {
        my $all_uploads = request->uploads;
        # $all_uploads->{'file_input_foo'} is a Dancer2::Core::Request::Upload object
        # $all_uploads->{'files_input'} is an arrayref of Dancer2::Core::Request::Upload objects

Note that you can also access the filename of the upload received via the body_parameters keyword:

    post '/some/route' => sub {
        # body_parameters->get('files_input') is the filename of the file uploaded

See Dancer2::Core::Request::Upload for details about the interface provided.


Returns a fully-qualified URI for the given path:

    get '/' => sub {
        redirect uri_for('/path');
        # can be something like: http://localhost:5000/path

Query string parameters can be provided by passing a hashref as a second param:

    uri_for('/path', { foo => 'bar' });
    # would return e.g. http://localhost:5000/path?foo=bar

By default, the parameters will be URL encoded:

    uri_for('/path', { foo => 'hope;faith' });
    # would return http://localhost:5000/path?foo=hope%3Bfaith

If desired (for example, if you've already encoded your query parameters and you want to prevent double encoding) you can disable URL encoding via a third parameter:

    uri_for('/path', { foo => 'qux%3Dquo' }, 1);
    # would return http://localhost:5000/path?foo=qux%3Dquo


Provides an accessor for variables shared between hooks and route handlers. Given a key/value pair, it sets a variable:

    hook before => sub {
        var foo => 42;

Later, route handlers and other hooks will be able to read that variable:

    get '/path' => sub {
        my $foo = var 'foo';


Returns the hashref of all shared variables set during the hook/route chain with the var keyword:

    get '/path' => sub {
        if (vars->{foo} eq 42) {


Logs a warning message through the current logger engine:

    warning "This is a warning";

See Dancer2::Core::Role::Logger for details on how to configure where log messages go.


Dancer Core Developers


This software is copyright (c) 2021 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.