docs: add Custom Python component documentation

_data/navigation.yml

@@ -567,6 +567,8 @@ items:
                 title: dbt Cloud Job Trigger
               - url: /components/applications/triggers/deepnote-notebook-execution-trigger/
                 title: Deepnote Notebook Execution Trigger
+          - url: /components/applications/custom-python/
+            title: Custom Python
           - url: /components/applications/data-gateway/
             title: Data Gateway
           - url: /components/applications/ai/

components/applications/custom-python/index.md

@@ -0,0 +1,122 @@
+---
+title: Custom Python
+permalink: /components/applications/custom-python/
+---
+
+* TOC
+{:toc}
+
+This component lets you run custom Python code directly in Keboola. Use it to call external APIs,
+process files, push data to third-party systems, or build any integration that isn't covered by an existing connector —
+all without leaving Keboola.
+
+{: .image-popup}
+![Screenshot - Custom Python Component Overview](/components/applications/custom-python/custom-python-0.png)
+
+## When to Use Custom Python
+
+| Scenario | Use |
+|---|---|
+| Transform or aggregate data already in Keboola Storage | [Python Transformation](/transformations/python-plain/) |
+| Connect to an external API or service, download or push data | **Custom Python** |
+| Store and use sensitive credentials (API keys, passwords, tokens) | **Custom Python** |
+| Share logic across multiple Keboola projects | **Custom Python** |
+
+## Key Features
+
+- **Secure parameters** — Encrypt API keys, tokens, and passwords directly in the Keboola UI using the `#` prefix.
+- **Flexible code source** — Write code in the Keboola UI, or load it from a Git repository.
+- **Clean environment** — Each run uses an isolated container. Install only the packages you need.
+- **Multiple Python versions** — Choose Python 3.12, 3.13, or 3.14.
+
+## Configuration
+
+[Create a new configuration](/components/#creating-component-configuration) of the **Custom Python** application.
+
+### Python Version
+
+{: .image-popup}
+![Screenshot - Python Version Selection](/components/applications/custom-python/custom-python-1.png)
+
+Select the Python version for your code:
+
+- **3.13** *(recommended)* — Isolated environment with only the packages you install.
+- **3.14** — Isolated environment (release candidate).
+- **3.12** — Isolated environment.
+- **base** — Shared environment (Python 3.10) with many pre-installed packages in legacy versions. Not recommended; will be deprecated in the future.
+
+{% include tip.html content="Use an isolated environment (Python 3.12 or newer) to avoid package version conflicts and keep your code maintainable." %}
+
+### Source Code & Dependencies
+
+Choose where your Python code comes from:
+
+**Enter manually into text areas below** *(default)*
+
+{: .image-popup}
+![Screenshot - Inline Code Source](/components/applications/custom-python/custom-python-3-code.png)
+
+Write or paste your code directly in the Keboola UI. Use the **Python Packages** field to list any extra packages to install.
+
+**Get from Git repository**
+
+Load code from a public or private Git repository. See [Git Configuration](#git-configuration) below.
+
+### User Parameters
+
+{: .image-popup}
+![Screenshot - User Parameters](/components/applications/custom-python/custom-python-2.png)
+
+Use **User Parameters** to pass configuration values to your code — for example an API base URL,
+a target table name, or debug flags. Enter them as a JSON object.
+
+Any key starting with `#` (e.g., `#api_key`) will be **encrypted** when you save the configuration.
+The decrypted value is available to your code at runtime via `CommonInterface`.
+
+## Git Configuration
+
+When using **Get from Git repository** as your code source, fill in the repository settings:
+
+{: .image-popup}
+![Screenshot - Git Repository Configuration](/components/applications/custom-python/custom-python-3-git.png)
+
+- **Repository URL** — Supports both HTTPS and SSH formats.
+- **Repository Visibility & Authentication** — Choose one of:
+  - **Public – None** — Public repository, no credentials needed.
+  - **Private – Personal Access Token** — The token is encrypted in Keboola Storage.
+  - **Private – SSH Key** — The private key is encrypted in Keboola Storage.
+- **Branch Name** — The branch to check out. Defaults to `main`. Use **List Branches** to pick from the repository.
+- **Script Filename** — The Python file to run. Defaults to `main.py`. Use **List Files** to pick from the repository.
+
+### Dependencies
+
+Place your dependency file in the repository root:
+
+- `pyproject.toml` + `uv.lock` *(recommended)* — Modern approach using [uv](https://docs.astral.sh/uv/).
+- `requirements.txt` — Legacy approach.
+
+If both are present, `pyproject.toml` + `uv.lock` takes precedence.
+
+## Writing Your Code
+
+Your code communicates with Keboola Storage and configuration via the
+[`keboola-component`](https://pypi.org/project/keboola-component/) Python library and `CommonInterface`.
+
+The following snippet is pre-filled in every new configuration and shows the basic pattern:
+
+```python
+from keboola.component import CommonInterface
+
+ci = CommonInterface()
+# Access user parameters defined in the configuration
+print(ci.configuration.parameters)
+```
+
+For the full `CommonInterface` reference — including reading input tables, writing output tables,
+working with files, state files, error handling, and logging — see the
+[Developer Documentation](https://developers.keboola.com/extend/component/tutorial/).
+
+## Example Repository
+
+We have prepared a [simple example project](https://github.com/keboola/component-custom-python-example-repo-1)
+to help you get started with running code from a Git repository. It can also serve as a template for your own projects.