Writing good commit messages is important. Not just for yourself, but for other developers on your project. This includes:

• new (or recently absent) developers who want to get up to speed on progress
• interested external parties who want to follow progress of the project
• people in the public (remember, we code in the open) who want to see our work, or learn from our practices
• any future developers (including yourself) who want to see why a change was made

• How to Write a Git Commit Message
• 5 useful tips for a better commit message
• Every line of code is always documented

A good commit message briefly summarises the "what" for scanning purposes, but also includes the "why". If the "what" in the message isn't enough, the diff is there as a fallback. This isn't true for the "why" of a change - this can be much harder or impossible to reconstruct, but is often of great significance.

Set cache headers

prefer:

Set cache headers

IE 6 was doing foo, so we need to do X.
See http://example.com/why-is-this-broken for more details.

A link to a ticket in an issue tracker should not be seen as an alternative to writing a commit message.

While a link can add some extra context for people reviewing a pull-request, the commit message should stand on its own. There's no guarantee that the link will continue to work in the future when someone is looking through the commit history to understand why a change was made.

If you are adding a link to a publicly viewable repository, ensure that the linked ticket is publicly viewable (and likely to remain so).

Commit messages should start with a one-line summary no longer than 50 characters. Various Git tools (including GitHub) use this as the commit summary, so you should format it like an email subject, with a leading capital and no full stop. The Git convention is to write these in the present tense. For example:

Leverage best-of-breed synergies going forward

You should leave a blank line before the rest of the commit message, which you should wrap at around 72 characters: this makes it easier to view commit messages in a terminal.

Taken from Tim Pope’s guidelines.

Capitalized, short (50 chars or less) summary

More detailed explanatory text, if necessary. Wrap it to about 72 characters or so. In some contexts, the first line is treated as the subject of an email and the rest of the text as the body. The blank line separating the summary from the body is critical (unless you omit the body entirely); tools like rebase can get confused if you run the two together.

Write your commit message in the present tense: "Fix bug" and not "Fixed bug." This convention matches up with commit messages generated by commands like git merge and git revert.

Further paragraphs come after blank lines.

• Bullet points are okay, too
• Typically a hyphen or asterisk is used for the bullet, preceded by a single space, with blank lines in between, but conventions vary here
• Use a hanging indent

You may often choose to work on a particular feature on a "feature branch" rather than directly on master. Indeed, given how cheap branches are in Git, this is positively encouraged.

You are encouraged to make liberal use of Git's history rewriting features while working locally, in order to arrange your commits into appropriate logical chunks that will make sense to your fellow developers. In particular, you may find git rebase --interactive very useful. You are also encouraged to avoid merge commits and use git rebase master instead. However, you should not rewrite commits that have been pushed unless you:

• are very sure that no-one else will be affected by you rewriting the branch history
• have an Extremely Good Reason. For example: someone has committed sensitive information (personally identifiable data, passwords and suchlike) and it needs purging from history

When in doubt you should err towards smaller commits, which can be rebased together later. It's harder to break large commits out into smaller chunks.

The smaller commits should still be logical chunks, but this will give context for a more specific change and make git tools like annotate and log more useful.

When merging from a feature branch to master (or any other mainline development branch), in particular one that has previously been shared with colleagues, you should use git merge's --no-ff option to preserve evidence of your feature branch in the repository history. This advice may be freely ignored for smaller local feature branches for which a fast-forward merge will look like any other routine development work on master.

Force pushing in git is a subject that attracts all kinds of religious battles. This advice is not about the merits of force pushing.

This is about how to use git push -f if and when you do use it.

Let's say you're working on a branch, 'foobar', and you decide to force push to the remote. So you do this:

$ git push -f

If anyone has committed anything to master¹ since you last pulled -- and if you've been working on the branch for any length of time this is pretty likely -- you will blow their changes away, because without arguments git will force push all remote-tracking branches.

So, if you ever need to force push the 'foobar' branch, please instead do

$ git push --force-with-lease origin foobar

--force-with-lease refuses to update a branch unless it is the state that we expect; i.e. nobody has updated the remote branch. See: https://developer.atlassian.com/blog/2015/04/force-with-lease/

You can also change git's default behaviour of pushing all tracked branches by doing git config --global push.default upstream, but you should probably get into the habit of typing out your intentions in full when doing a destructive operation like force pushing, otherwise disaster will strike when you use someone else's differently-configured git, or miss a step when configuring a new machine.