> ## Documentation Index
> Fetch the complete documentation index at: https://prefect-bd373955-pytest-markdown.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# How to Contribute

> Learn how to set up Prefect for development and experimentation.

## Set up a development environment

First, download the source code and install an editable copy of the Prefect Python package:

```bash
# Clone the repository
git clone https://github.com/PrefectHQ/prefect.git
cd prefect

# We recommend using a virtual environment. Below we use venv

python -m venv .venv
source .venv/bin/activate

# Install the package with development dependencies

pip install -e ".[dev]"

# Set up pre-commit hooks for required formatting

pre-commit install

```

If you don't want to install the pre-commit hooks, manually install the formatting dependencies with:

```bash
pip install $(./scripts/precommit-versions.py)

```

Run `ruff check` and `ruff format`.

After installation, you can run the test suite with `pytest`:

```bash
# Run all the tests
pytest tests

# Run a subset of tests

pytest tests/test_flows.py

```

<Tip>
  **Build the Prefect UI**

  If you intend to run a local Prefect server during development, first build the UI.
  See [UI development](#ui-development) for instructions.
</Tip>

### Developer tooling

The Prefect CLI provides several helpful commands to aid development.

Start all services with hot-reloading on code changes (requires installation of UI dependencies):

```bash
prefect dev start
```

Start a Prefect API that reloads on code changes:

```bash
prefect dev api
```

## UI development

Developing the Prefect UI requires installation of [npm](https://github.com/npm/cli).
We recommend using [nvm](https://github.com/nvm-sh/nvm) to manage Node.js versions.
Once installed, run `nvm use` from the root of the Prefect repository to initialize the proper version of `npm` and `node`.

Start a development UI that reloads on code changes:

```bash
prefect dev ui
```

Build the static UI (the UI served by `prefect server start`):

```bash
prefect dev build-ui
```

## Docs development

We use [Mintlify](https://mintlify.com/) to host and build the documentation.

The main branch of the [prefecthq/prefect](https://github.com/PrefectHQ/prefect) GitHub repository is used to build the Prefect 3.0rc docs at [docs-3.prefect.io](https://docs-3.prefect.io) temporarily.

The 2.x docs are hosted at [docs.prefect.io](https://docs.prefect.io) and built from the 2.x branch of prefecthq/prefect.

Make sure you have a recent version of Node.js installed. We recommend using [nvm](https://github.com/nvm-sh/nvm) to manage Node.js versions.

1. Clone this repository.
2. Run `cd docs` to navigate to the docs directory.
3. Run `nvm use node` to use the correct Node.js version.
4. Run `npm i -g mintlify` to install Mintlify.
5. Run `mintlify dev` to start the development server.

Your docs should now be available at `http://localhost:3000`.

See the [Mintlify documentation](https://mintlify.com/docs/development) for more information on how install Mintlify, build previews, and use Mintlify's features while writing docs.

`.mdx` files are Markdown files that can contain JavaScript and React components. They are used to create interactive documentation.

## Add database migrations

To make changes to a table, first update the SQLAlchemy model in `src/prefect/server/database/orm_models.py`. For example,
to add a new column to the `flow_run` table, add a new column to the `FlowRun` model:

```python
# src/prefect/server/database/orm_models.py

@declarative_mixin
class ORMFlowRun(ORMRun):
    """SQLAlchemy model of a flow run."""
    ...
    new_column = Column(String, nullable=True) # <-- add this line
```

Next, you will generate new migration files. You must generate a new migration file for each database type.
Migrations are generated for whatever database type `PREFECT_API_DATABASE_CONNECTION_URL` is set to.
See [how to set the database connection URL](/3.0rc/manage/self-host#database-settings) for
each database type.

To generate a new migration file, run:

```bash
prefect server database revision --autogenerate -m "<migration name>"
```

Make your migration name brief but descriptive. For example:

* `add_flow_run_new_column`
* `add_flow_run_new_column_idx`
* `rename_flow_run_old_column_to_new_column`

The `--autogenerate` flag automatically generates a migration file based on the changes to the models.

<Warning>
  **Always inspect the output of `--autogenerate`**

  `--autogenerate` generates a migration file based on the changes to the models. However, it is not perfect. Check
  the file to make sure it only includes the changes you want. Additionally, you may need to remove extra statements that
  were included and not related to your change.
</Warning>

The new migration is in the `src/prefect/server/database/migrations/versions/` directory. Each database type has its
own subdirectory. For example, the SQLite migrations are stored in `src/prefect/server/database/migrations/versions/sqlite/`.

After you inspect the migration file, you can apply the migration to your database by running:

```bash
prefect server database upgrade -y
```

Once you successfully create and apply migrations for all database types, update `MIGRATION-NOTES.md` to
document your additions.