Skip to content

Development - Contributing

First, you might want to see the basic ways to help FastAPI and get help.


If you already cloned the fastapi repository and you want to deep dive in the code, here are some guidelines to set up your environment.

Virtual environment with venv

You can create an isolated virtual local environment in a directory using Python's venv module. Let's do this in the cloned repository (where the requirements.txt is):

$ python -m venv env

That will create a directory ./env/ with the Python binaries, and then you will be able to install packages for that local environment.

Activate the environment

Activate the new environment with:

$ source ./env/bin/activate
$ .\env\Scripts\Activate.ps1

Or if you use Bash for Windows (e.g. Git Bash):

$ source ./env/Scripts/activate

To check it worked, use:

$ which pip

$ Get-Command pip


If it shows the pip binary at env/bin/pip then it worked. 🎉

Make sure you have the latest pip version on your local environment to avoid errors on the next steps:

$ python -m pip install --upgrade pip

---> 100%


Every time you install a new package with pip under that environment, activate the environment again.

This makes sure that if you use a terminal program installed by that package, you use the one from your local environment and not any other that could be installed globally.

Install requirements using pip

After activating the environment as described above:

$ pip install -r requirements.txt

---> 100%

It will install all the dependencies and your local FastAPI in your local environment.

Using your local FastAPI

If you create a Python file that imports and uses FastAPI, and run it with the Python from your local environment, it will use your cloned local FastAPI source code.

And if you update that local FastAPI source code when you run that Python file again, it will use the fresh version of FastAPI you just edited.

That way, you don't have to "install" your local version to be able to test every change.

Technical Details

This only happens when you install using this included requirements.txt instead of running pip install fastapi directly.

That is because inside the requirements.txt file, the local version of FastAPI is marked to be installed in "editable" mode, with the -e option.

Format the code

There is a script that you can run that will format and clean all your code:

$ bash scripts/

It will also auto-sort all your imports.

For it to sort them correctly, you need to have FastAPI installed locally in your environment, with the command in the section above using -e.


First, make sure you set up your environment as described above, that will install all the requirements.

Docs live

During local development, there is a script that builds the site and checks for any changes, live-reloading:

$ python ./scripts/ live

<span style="color: green;">[INFO]</span> Serving on
<span style="color: green;">[INFO]</span> Start watching changes
<span style="color: green;">[INFO]</span> Start detecting changes

It will serve the documentation on

That way, you can edit the documentation/source files and see the changes live.


Alternatively, you can perform the same steps that scripts does manually.

Go into the language directory, for the main docs in English it's at docs/en/:

$ cd docs/en/

Then run mkdocs in that directory:

$ mkdocs serve --dev-addr 8008

Typer CLI (optional)

The instructions here show you how to use the script at ./scripts/ with the python program directly.

But you can also use Typer CLI, and you will get autocompletion in your terminal for the commands after installing completion.

If you install Typer CLI, you can install completion with:

$ typer --install-completion

zsh completion installed in /home/user/.bashrc.
Completion will take effect once you restart the terminal.

Docs Structure

The documentation uses MkDocs.

And there are extra tools/scripts in place to handle translations in ./scripts/


You don't need to see the code in ./scripts/, you just use it in the command line.

All the documentation is in Markdown format in the directory ./docs/en/.

Many of the tutorials have blocks of code.

In most of the cases, these blocks of code are actual complete applications that can be run as is.

In fact, those blocks of code are not written inside the Markdown, they are Python files in the ./docs_src/ directory.

And those Python files are included/injected in the documentation when generating the site.

Docs for tests

Most of the tests actually run against the example source files in the documentation.

This helps to make sure that:

  • The documentation is up-to-date.
  • The documentation examples can be run as is.
  • Most of the features are covered by the documentation, ensured by test coverage.

Apps and docs at the same time

If you run the examples with, e.g.:

$ uvicorn tutorial001:app --reload

<span style="color: green;">INFO</span>:     Uvicorn running on (Press CTRL+C to quit)

as Uvicorn by default will use the port 8000, the documentation on port 8008 won't clash.


Help with translations is VERY MUCH appreciated! And it can't be done without the help from the community. 🌎 🚀

Here are the steps to help with translations.

Tips and guidelines

  • Check the currently existing pull requests for your language. You can filter the pull requests by the ones with the label for your language. For example, for Spanish, the label is lang-es.

  • Review those pull requests, requesting changes or approving them. For the languages I don't speak, I'll wait for several others to review the translation before merging.


You can add comments with change suggestions to existing pull requests.

Check the docs about adding a pull request review to approve it or request changes.

  • Check if there's a GitHub Discussion to coordinate translations for your language. You can subscribe to it, and when there's a new pull request to review, an automatic comment will be added to the discussion.

  • If you translate pages, add a single pull request per page translated. That will make it much easier for others to review it.

  • To check the 2-letter code for the language you want to translate, you can use the table List of ISO 639-1 codes.

Existing language

Let's say you want to translate a page for a language that already has translations for some pages, like Spanish.

In the case of Spanish, the 2-letter code is es. So, the directory for Spanish translations is located at docs/es/.


The main ("official") language is English, located at docs/en/.

Now run the live server for the docs in Spanish:

// Use the command "live" and pass the language code as a CLI argument
$ python ./scripts/ live es

<span style="color: green;">[INFO]</span> Serving on
<span style="color: green;">[INFO]</span> Start watching changes
<span style="color: green;">[INFO]</span> Start detecting changes


Alternatively, you can perform the same steps that scripts does manually.

Go into the language directory, for the Spanish translations it's at docs/es/:

$ cd docs/es/

Then run mkdocs in that directory:

$ mkdocs serve --dev-addr 8008

Now you can go to and see your changes live.

You will see that every language has all the pages. But some pages are not translated and have an info box at the top, about the missing translation.

Now let's say that you want to add a translation for the section Features.

  • Copy the file at:
  • Paste it in exactly the same location but for the language you want to translate, e.g.:


Notice that the only change in the path and file name is the language code, from en to es.

If you go to your browser you will see that now the docs show your new section (the info box at the top is gone). 🎉

Now you can translate it all and see how it looks as you save the file.

New Language

Let's say that you want to add translations for a language that is not yet translated, not even some pages.

Let's say you want to add translations for Creole, and it's not yet there in the docs.

Checking the link from above, the code for "Creole" is ht.

The next step is to run the script to generate a new translation directory:

// Use the command new-lang, pass the language code as a CLI argument
$ python ./scripts/ new-lang ht

Successfully initialized: docs/ht

Now you can check in your code editor the newly created directory docs/ht/.

That command created a file docs/ht/mkdocs.yml with a simple config that inherits everything from the en version:

INHERIT: ../en/mkdocs.yml


You could also simply create that file with those contents manually.

That command also created a dummy file docs/ht/ for the main page, you can start by translating that one.

You can continue with the previous instructions for an "Existing Language" for that process.

You can make the first pull request with those two files, docs/ht/mkdocs.yml and docs/ht/ 🎉

Preview the result

As already mentioned above, you can use the ./scripts/ with the live command to preview the results (or mkdocs serve).

Once you are done, you can also test it all as it would look online, including all the other languages.

To do that, first build all the docs:

// Use the command "build-all", this will take a bit
$ python ./scripts/ build-all

Building docs for: en
Building docs for: es
Successfully built docs for: es

This builds all those independent MkDocs sites for each language, combines them, and generates the final output at ./site/.

Then you can serve that with the command serve:

// Use the command "serve" after running "build-all"
$ python ./scripts/ serve

Warning: this is a very simple server. For development, use mkdocs serve instead.
This is here only to preview a site with translations already built.
Make sure you run the build-all command first.
Serving at:

Translation specific tips and guidelines

  • Translate only the Markdown documents (.md). Do not translate the code examples at ./docs_src.

  • In code blocks within the Markdown document, translate comments (# a comment), but leave the rest unchanged.

  • Do not change anything enclosed in "``" (inline code).

  • In lines starting with === or !!!, translate only the "... Text ..." part. Leave the rest unchanged.

  • You can translate info boxes like !!! warning with for example !!! warning "Achtung". But do not change the word immediately after the !!!, it determines the color of the info box.

  • Do not change the paths in links to images, code files, Markdown documents.

  • However, when a Markdown document is translated, the #hash-parts in links to its headings may change. Update these links if possible.

    • Search for such links in the translated document using the regex #[^# ].
    • Search in all documents already translated into your language for For example VS Code has an option "Edit" -> "Find in Files".
    • When translating a document, do not "pre-translate" #hash-parts that link to headings in untranslated documents.


There is a script that you can run locally to test all the code and generate coverage reports in HTML:

$ bash scripts/

This command generates a directory ./htmlcov/, if you open the file ./htmlcov/index.html in your browser, you can explore interactively the regions of code that are covered by the tests, and notice if there is any region missing.