Mojolicious::Guides::FAQ - Frequently Asked Questions


This document contains the most frequently asked questions about Mojolicious together with the right answers.


Why doesn't Mojolicious have any dependencies?

We are optimizing Mojolicious for user-friendliness and development speed without compromises. While there are no rules in Mojolicious::Guides::CodingGuidelines that forbid dependencies, we do currently discourage adding non-optional ones in favor of a faster and more painless installation process. And we do in fact already use several optional CPAN modules such as IO::KQueue, IO::Epoll, IO::Socket::IP, IO::Socket::SSL, Net::Rendezvous::Publish and Plack to provide advanced functionality if they are installed.

Why reinvent wheels?

Because we can make them rounder. Components specifically designed for user-friendliness and development speed are not easy to come by. While we are strong believers of the Perl mantra "There is more than one way to do it.", we also believe that well designed defaults result in a much more pleasant user experience. We want the best of both worlds.

What about backwards compatibility?

In conformance with Mojolicious::Guides::CodingGuidelines, we will always deprecate a feature for at least one major release before removing or changing it in incompatible ways. New features can however be marked as experimental to explicitly exclude them from these rules. This gives us the necessary freedom to ensure a healthy future for Mojolicious. So, as long as you are not using anything marked experimental, untested or undocumented, you can always count on backwards compatibility, everything else would be considered a bug.

Why is using Perl 5.8.x such a bad idea?

The Perl 5.8 family has reached the end of its life a few years ago and is no longer getting updated by the community. It contains very serious flaws, especially around the regular expression engine, that will never get fixed and are likely put your applications at risk. While your operating system vendor might keep it compiling on their platform, they will not fix these issues. Therefore we highly recommend that you upgrade as soon as possible!

While we have considered officially deprecating Perl 5.8.x support in Mojolicious altogether, it would sadly be too much of a competitive disadvantage at this point in time.

What does the error "Maximum message size exceeded." mean?

To protect your applications from excessively large requests and responses, our HTTP parser has a cap after which it will automatically stop accepting new data, and in most cases force the connection to be dropped. This limit is around 5MB by default, you can use the MOJO_MAX_MESSAGE_SIZE environment variable to change this value.

What does the error "Maximum line size exceeded." mean?

This is a very similar protection mechanism to the one described in the previous answer, but a little more specific. It limits the maximum length of any \r\n terminated part of a HTTP message, such as request line, status line and headers. This limit is around 10KB by default, you can use the MOJO_MAX_LINE_SIZE environment variable to change this value.

What does "Your secret passphrase needs to be changed!!!" mean?

Mojolicious uses a secret passphrase for security features such as signed cookies. It defaults to the name of your application, which is not very secure, so we added this log message as a reminder. You can change the passphrase with the secret attribute of Mojolicious.

  app->secret('My very secret passphrase.');

Does Mojolicious run on Windows systems?

Sure it does! Right now there are two different ways of running Perl on the Windows platform. One is Strawberry Perl and the other is ActiveState Perl. Both are capable Perl distributions which are stable, mature and ready for production. But Strawberry Perl is quite a bit better at dealing with the CPAN and especially XS based modules due to its remarkable toolchain. With it you can even install modules straight from the source as you would do on a Unix based machine.

Is it possible to run the built-in webserver on Windows?

It is! The built-in webserver is great way to run your Mojolicious web application on any platform. See Mojolicious::Guides::Cookbook for more information about running and deploying Mojolicious applications.

Whats the easiest way to install Mojolicious on UNIX?

Quite possibly this oneliner.

  sudo sh -c "curl -L | perl - Mojolicious"

I think Mojolicious is awesome, how can i support you guys?

Share your success story via blog or twitter, get more people hooked! :)

I think i have found a bug, what should i do now?

First make sure you are using the latest version of Mojolicious, it is quite likely that the bug has already been fixed. If that doesn't help prepare a test case demonstrating the bug, you are not expected to fix it yourself, but you'll have to make sure the developers can replicate your problem. Sending in your whole application generally does more harm than good, the t directory of this distribution has many good examples for how to do it right. Writing a test is usually the hardest part of fixing a bug, so the better your test case the faster it can be fixed. ;)

Once that's done you can contact the developers via GitHub (, mailing list ( or IRC (#mojo on

If you decide to fix the bug yourself make sure to also take a look at Mojolicious::Guides::CodingGuidelines.

Which namespace should i use for Mojolicious plugins?

For all new plugins that you might want to release to CPAN we suggest using the "Mojolicious::Plugin" namespace. While "MojoX" has been used a lot in the past, it is now deprecated.


You can continue with Mojolicious::Guides now or take a look at the Mojolicious wiki, which contains a lot more documentation and examples by many different authors.