leverages mercurial's built-in collaboration tools for contributing to projects hosted here. This guide will help you get started. If you run into any trouble, please send an email to the mailing list for help.

Golden rule: Do not copy-paste the output of hg export into your typical mail client.

For everyone

Before you dig too far into this guide, you should make sure that your email client is configured to use plain text emails. By default, many email clients compose emails with HTML, so you can use rich text formatting. Rich text is not desirable for development-oriented email conversations, so you should disable this feature and send your email as plain text. Every email client is different, you should research the options for your specific client. HTML emails are rejected by all services.

For real-world examples of how the discussions described in this document play out, check out the mailing list.

Unsure if your setup is correct? Try sending the patch to for feedback first - make sure you mention in the email that you want feedback.

For contributors

Preparing your changes

There's no need to fork the repository you want to contribute to -- simply use hg clone to obtain a local copy of the mercurial repository and work normally. Be deliberate about your commits -- use meaningful commit messages and take special care to commit your work in the form of logically separate changes. When it comes time to review your work, your commit history is an important tool for the reviewer and will be closely examined.

Find out where to send your changes

This workflow is optional for projects hosted on and each project will have different requirements - review them carefully. To use this guide, you need to find an email address to send your work to - this will often be a mailing list on You will also want to find people who can help review your changes - look for dedicated maintainers for the modules you're working on, or use hg annotate to find people who have recently worked on similar code.

Configure hg email

When you've collected a list of email addresses to send your work to, we can use hg email to do the job. Its purpose is to convert your mercurial commits into emails with hg export and connect to your mail server to deliver them with SMTP.

If you've never used hg email before, you will need to do some one-time setup to enable the email command (which isn't accessible by default, but is available in the patchbomb extension which ships with Mercurial), and introduce it to your SMTP server. The connection details vary between mail providers, but you're looking for information which is suitable for filling out these config fields in mercurial's configuration file:

patchbomb =

host =
port = 587
tls = smtps
username =

You can also set your SMTP password as smtp.password. If you don't, you will be prompted for it when it's needed.

Send the patches along

When you've configured hg email, completed your work, and you're ready to send your patches in, you can run hg email -r [rev]. The [rev] here is the same as any other revision number, identifier, or name. The command will prepare a patch for that commit and send it through your mail server.

A few things of note:

  • hg email -o [dest] will prepare patches for any revision not already in the upstream [dest] repository (i.e. anything that would show up with hg outgoing [dest]). If you have configured the default destination (in the [paths] section), you can even just do hg email -o!
  • hg email -r tip includes the last commit.
  • You can use revsets to specify revision ranges, like, say, hg email -r 3000:3005 for sending patches for revisions 3000 through 3005.
  • Add the --confirm option to give you an extra step to catch mistakes.

Mercurial might prompt you for more information before sending the email. For instance, it might ask you what your email address is. Although it uses what it found in your config's ui.username, it wants to be sure. You can skip that step by setting the email.from option in your config too:

from = Your Name <>

If you're sending more than one patch at once, Mercurial will ask you to write an introduction email to the patch series. In many cases, this is unnecessary, so you can optionally disable this feature in your config (you can always pass --intro to hg email if you want it back):

intro = never

Handling feedback

You will likely receive replies to your email with feedback on your changes. This is normal! Use tools like [hg commit --amend][amend] and hg rebase to continue improving your patch set and iterating on feedback. When you're ready to submit the next version of your patches, use hg email normally, except:

  • Add --flag V2 to indicate that this is version 2 of your patch (or whatever number is appropriate).
  • Optionally, add --in-reply-to [msgid], where [msgid] is the message ID of the last email in the thread. On you can get this by clicking details on the email in question. If you can't find this, don't sweat it, it's no big deal.

Pulling from upstream

As you continue to work, you may want to pull from the upstream, and you almost certainly don't want to create a merge commit when you have work in progress or unmerged changes in your history. To this end, you should generally use hg pull --rebase to fetch the latest changes from upstream.

Extra tips

Here are a few extra tricks you might find useful with hg email.

Sending emails to the same address every time

If you send emails for a project to the same mailing list every time, you might find it useful to set the default destination address. Edit the project's repository config (.hg/hgrc) with:

to =

Specifying a subproject for shared lists

Some projects have several repositories being discussed on a single mailing list, and it's often helpful to specify the particular repository your patch pertains to.

If you're just doing this once, add --flags to hg email. You can specify it multiple times if you also need to specify --flags V2. For instance:

hg email --flags 'example' -o

You can also specify this as the default for that mercurial repository by editing its config (.hg/hgrc):

flagtemplate = example {flags}

The {flags} placeholder indicates where other --flags will go in the email subject (in thise case: after example).

For maintainers

Tell people how to contribute

The first thing you need to do is help potential contributors figure out how to contact you. The easiest way is to do nothing - mercurial records your email with every commit, so someone with a copy of your mercurial repository can figure out how to contact you. You'll probably want to make it a bit easier on them, though.

We recommend setting up a mailing list on for this purpose. Once you do, you will get an email address for contributors to submit patches to. Write this into your docs! You will probably also want to link to the archives so that potential contributors can read other people's work to get a feel for your submission process.

Reviewing patches

When a patch comes in, you should review it carefully. Read the code, apply the patch locally and make sure it compiles, test the changes, and so on. During this process you'll probably come up with feedback on the patch. Pull open that email client and compose a reply to the patch author. When your client composes the reply, don't be afraid to slice and dice the email you're replying to - trim out the fat and only include specific lines that you want to comment on.

If you only have small comments here and there, feel free to make the changes yourself, again utilizing hg commit --amend and hg rebase to your heart's content. You may be wise to point out these small errors when you thank the submitter for their patch, however, if you don't want to see the same errors in future patches.

Applying patches

In order to integrate the changes, you need to apply the patch. The tool for this is hg import. The difficult part here is going to be obtaining a copy of the email to provide to hg import. Some clients like mutt make this easy (in mutt, you can use the | key to pipe an email directly to hg import -), or tools like offlineimap can help (or a combination of the two!). Most popular end-user clients do not provide this option. If you're in this boat, the easiest way to get a raw email is to use the raw link on, which is hidden away under the details button.

If you copy the link to the raw email from, you can pass that directly to hg import and it will download it for you:

hg import

You can also just run hg import - paste the patch into it, followed by Ctrl+D.

One applied, you can make these commits available upstream by using hg push normally. Don't forget to send the contributor a thank you email!