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+Contribution Guidelines
+=======================
+
+<!-- markdown-toc start - Don't edit this section. Run M-x markdown-toc-refresh-toc -->
+**Table of Contents**
+
+- [Contribution Guidelines](#contribution-guidelines)
+    - [Before making a change](#before-making-a-change)
+    - [Commit messages](#commit-messages)
+    - [Commit content](#commit-content)
+    - [Code quality](#code-quality)
+    - [Builds & tests](#builds--tests)
+    - [Submitting changes](#submitting-changes)
+
+<!-- markdown-toc end -->
+
+This is a loose set of "guidelines" for contributing to the depot. Please note
+that we will not accept any patches that don't follow these guidelines.
+
+Also consider the [code of conduct](./CODE_OF_CONDUCT.md). No really,
+you should.
+
+## Before making a change
+
+Before making a change, consider your motivation for making the change.
+Documentation updates, bug fixes and the like are *always* welcome.
+
+When adding a feature you should consider whether it is only useful for your
+particular use-case or whether it is generally applicable for other users of the
+project.
+
+When in doubt - just ask! You can reach out to us at
+[depot@tazj.in](mailto:depot@tazj.in) or on Twitter, IRC, etc.
+
+## Commit messages
+
+All commit messages should be structured like this:
+
+```
+type(scope): Subject line with at most a 68 character length
+
+Body of the commit message with an empty line between subject and
+body. This text should explain what the change does and why it has
+been made, *especially* if it introduces a new feature.
+
+Relevant issues should be mentioned if they exist.
+```
+
+Where `type` can be one of:
+
+* `feat`: A new feature has been introduced
+* `fix`: An issue of some kind has been fixed
+* `docs`: Documentation or comments have been updated
+* `style`: Formatting changes only
+* `refactor`: Hopefully self-explanatory!
+* `test`: Added missing tests / fixed tests
+* `chore`: Maintenance work
+* `subtree`: Operations involving `git subtree`
+
+And `scope` should refer to some kind of logical grouping inside of the project.
+
+It does not make sense to include the full path unless it aids in
+disambiguating. For example, when changing the configuration of the host
+`whitby` at `//ops/machines/whitby` it is enough to write `feat(whitby): ...`.
+
+Please take a look at the existing commit log for examples.
+
+## Commit content
+
+Multiple changes should be divided into multiple git commits whenever possible.
+Common sense applies.
+
+The fix for a single-line whitespace issue is fine to include in a different
+commit. Introducing a new feature and refactoring (unrelated) code in the same
+commit is not fine.
+
+`git commit -a` is generally **taboo**.
+
+In my experience making "sane" commits becomes *significantly* easier as
+developer tooling is improved. The interface to `git` that I recommend is
+[magit][]. Even if you are not yet an Emacs user, it makes sense to install
+Emacs just to be able to use magit - it is really that good.
+
+For staging sane chunks on the command line with only git, consider `git add
+-p`.
+
+## Code quality
+
+This one should go without saying - but please ensure that your code quality
+does not fall below the rest of the project. This is of course very subjective,
+but as an example if you place code that throws away errors into a block in
+which errors are handled properly your change will be rejected.
+
+In my experience there is a strong correlation between the visual appearance of
+a code block and its quality. This is a simple way to sanity-check your work
+while squinting and keeping some distance from your screen ;-)
+
+## Builds & tests
+
+All projects are built using [Nix][] to avoid "build pollution" via the user's
+environment.
+
+If you have Nix installed and are contributing to a project tracked in this
+repository, you can usually build the project by calling `nix-build -A
+path.to.project`.
+
+For example, to build a project located at `//tools/foo` you would call
+`nix-build -A tools.foo`
+
+If the project has tests, check that they still work before submitting your
+change.
+
+## Submitting changes
+
+The code review & change submission process is described in the [code
+review][] documentation.
+
+[magit]: https://magit.vc/
+[Nix]: https://nixos.org/nix/
+[code review]: ./REVIEWS.md