The [issue tracker](https://github.com/OpenTTD/OpenTTD/issues) is the preferred channel for [bug reports](#bug-reports), but please respect the following restrictions:
Use [GitHub's "reactions" feature](https://github.com/blog/2119-add-reactions-to-pull-requests-issues-and-comments) instead.
We reserve the right to delete comments which violate this rule.
* Please **do not** open issues or pull requests regarding add-on content in NewGRF, GameScripts, AIs, etc.
These are created by third-parties. Please try [irc](https://wiki.openttd.org/IRC_channel) or the [forums](https://www.tt-forums.net/) to discuss these.
A bug is a _demonstrable problem_ that is caused by the code in the repository.
Good bug reports are extremely helpful, so thanks!
Guidelines for bug reports:
0. Please don't report issues with games where you changed NewGRFs.
1. Please don't report issues with modified versions of OpenTTD (patchpacks and similar).
2.**Use the GitHub issue search** --- check if the issue has already been
reported.
3.**Check if the issue has been fixed** --- try to reproduce it using the latest `nightly` build of OpenTTD, available from https://www.openttd.org
4.**Isolate the problem** --- ideally create reproduceable steps with an attached savegame and screenshots. Try to use few or no NewGRFs, AIs etc if possible.
A good bug report shouldn't leave others needing to chase you up for more information.
Please try to be as detailed as possible in your report.
* What is your environment?
* What steps will reproduce the issue?
* Which operating system(s) experience the problem?
* What would you expect to be the outcome?
All these details will help people to fix any potential bugs.
Example:
> Short and descriptive example bug report title
>
> A summary of the issue and the OS environment in which it occurs. If
> suitable, include the steps required to reproduce the bug.
>
> 1. This is the first step
> 2. This is the second step
> 3. Further steps, etc.
>
> Attached savegame
> Attached screenshots showing the issue
> Crashlogs if the bug causes a crash
>
> Any other information you want to share that is relevant to the issue being
> reported. This might include the lines of code that you have identified as
> causing the bug, and potential solutions (and your opinions on their
Before opening a feature request, please take a moment to find out whether your idea fits with the [scope and goals](./CONTRIBUTING.md#project-goals) of the project.
Keeping issues around with "a good idea" or "not really a bug but we should maybe fix it" turns out to have the reversed effect: nobody looks at it anymore.
Although we really appreciate feedback and ideas, we will close feature requests that we don't expect to fulfill in the next year.
Many of those ideas etc do have a place on the [forums](https://www.tt-forums.net); and if enough people like it, someone will stand up and make it.
It's usually best discuss in [irc](https://wiki.openttd.org/IRC_channel) before opening a feature request or working on a large feature in a fork.
Discussion in irc can take time, but it can be productive and avoid disappointment :)
**Please do ask first** before embarking on any significant pull request (e.g. implementing features, refactoring code, porting to a different language), otherwise you risk spending a lot of time working on something that the project's developers might not want to merge into the project.
Every pull request should have a clear scope, with no unrelated commits.
[Code style](https://wiki.openttd.org/Coding_style) must be complied with for pull requests to be accepted; this also includes [commit message format](https://wiki.openttd.org/Coding_style#Commit_message).
4. Commit your changes in logical chunks. Please adhere to these [git commit message guidelines](https://wiki.openttd.org/Commit_style#Commit_message) or your code is unlikely to be merged into the main project.
Use Git's [interactive rebase](https://help.github.com/articles/interactive-rebase) feature to tidy up your commits before making them public.
5. Locally rebase the upstream development branch into your topic branch:
```bash
git fetch upstream
git rebase upstream/master
```
6. Push your topic branch up to your fork the first time:
There is no single source for OpenTTD development docs. It's a complex project with a long history, and multiple APIs.
A good entry point is [Development](https://wiki.openttd.org/Development) on the OpenTTD wiki; this provides links to wiki documentation and other sources.
The GitHub repo also includes some non-comprehensive documentation in [/docs](./docs).
You may also want the guide to [compiling OpenTTD](./COMPILING.md).
To please everyone, the official branch tries to stay close to the original gameplay; after all, that is what everyone brought here.
The preferred method to alter and extent the gameplay is via add-ons like NewGRF and GameScripts.
For a long time, the official branch was also open to features which could be enabled/disabled, but the corner-cases that came with some configurations have rendered some parts of the code very complicated.
Today, new features have to work with all the already existing features, which is not only challenging in corner cases, but also requires spending considerable more work than just "making it work in the game mode that I play".
The preferred method to introduce new gameplay features is to extend the content APIs, supporting ever more add-on content / mods.
This moves conflict-solving away from the codebase to content authors / players.
It is more accepted for add-ons not working together than the base game not working with certain setting combinations.
In general the game should allow anything that doesn't violate basic rules, but it should warn players if they take potentially dangerous or "stupid" actions.
For example, players are not prevented from starting vehicles without orders, but will receive a warning about vehicles having too few orders.
This lack of limitation has led to players challenging themselves to create networks where all vehicles have no orders, increasing gameplay possibilities.
Fork! There is a rich history of experimental patches for OpenTTD.
Many of these will never be accepted for core, but are creative and interesting ways to modify OpenTTD.
Sometimes patches are combined into long-running patchpacks, modified OpenTTD versions which can be downloaded by anyone, or modified OpenTTD clients for dedicated multiplayer servers.
One of the reasons to keep core relatively stable is to make life easier for patch authors and patchpack maintainers where possible.
Patchpack discussions and related topics may be found in community sites such as [TT-Forums development section](https://www.tt-forums.net/viewforum.php?f=33).
We would like to make you aware that contributing to OpenTTD via git will permanently store the name and email address you provide as well as the actual changes and the time and date you made it inside git's version history.
This is inevitable, because it is a main feature of git.
If you are concerned about your privacy, we strongly recommend to use "Anonymous <anonymous@openttd.org>" as the git commit author. We might refuse anonymous contributions if malicious intent is suspected.
Please note that the contributor identity, once given, is used for copyright verification and to provide proof should a malicious commit be made.
As such, the [EU GDPR](https://www.eugdpr.org/key-changes.html) "right to be forgotten" does not apply, as this is an overriding legitimate interest.
Please also note that your commit is public and as such will potentially be processed by many third-parties.
Git's distributed nature makes it impossible to track where exactly your commit, and thus your personal data, will be stored and be processed.
If you would not like to accept this risk, please do either commit anonymously or refrain from contributing to the OpenTTD project.
This contributing guide is adapted from [Bootstrap](https://github.com/twbs/bootstrap/blob/master/CONTRIBUTING.md) under the [Creative Commons Attribution 3.0 Unported License](https://github.com/twbs/bootstrap/blob/master/docs/LICENSE) terms for Bootstrap documentation.
The GDPR notice is adapted from [rsyslog](https://github.com/rsyslog/rsyslog/blob/master/CONTRIBUTING.md) under the [GNU General Public License](https://github.com/rsyslog/rsyslog/blob/master/COPYING).
