> ## Documentation Index
> Fetch the complete documentation index at: https://langchain-5e9cc07a-preview-assist-1763402091-b822589.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Contributing to code

Code contributions are always welcome! Whether you're fixing bugs, adding features, or improving performance, your contributions help deliver a better developer experience for thousands of developers.

<Note>
  Before submitting large **new features or refactors**, please first discuss your ideas in [the forum](https://forum.langchain.com/). This ensures alignment with project goals and prevents duplicate work.

  This does not apply to bugfixes or small improvements, which you can contribute directly via pull requests. Be sure to link any relevant issues in your PR description. Use <Tooltip tip="(e.g. `Fixes #123`)">closing keywords</Tooltip> to automatically close issues when the PR is merged.

  New integrations should follow the [integration guidelines](/oss/python/contributing#add-a-new-integration).
</Note>

## Philosophy

Aim to follow these core principles for all code contributions:

<CardGroup cols={2}>
  <Card title="Backwards compatibility" icon="shield" href="#backwards-compatibility" arrow>
    Maintain stable public interfaces and avoid breaking changes
  </Card>

  <Card title="Testing first" icon="flask" href="#testing-requirements" arrow>
    Every change must include comprehensive tests to verify correctness and prevent regressions
  </Card>

  <Card title="Code quality" icon="star" href="#code-quality-standards" arrow>
    Follow consistent style, documentation, and architecture patterns
  </Card>

  <Card title="Security focused" icon="lock" href="#security-guidelines" arrow>
    Prioritize secure coding practices and vulnerability prevention
  </Card>
</CardGroup>

***

## Getting started

### Quick fix: submit a bugfix

For simple bugfixes, you can get started immediately:

<Steps>
  <Step title="Fork the repository">
    Fork the [LangChain](https://github.com/langchain-ai/langchain) or [LangGraph](https://github.com/langchain-ai/langgraph) repo to your <Tooltip tip="If you fork to an organization account, maintainers will be unable to make edits.">personal GitHub account</Tooltip>
  </Step>

  <Step title="Clone and setup">
    ```bash theme={null}
    git clone https://github.com/your-username/name-of-forked-repo.git

    # For instance, for LangChain:
    git clone https://github.com/parrot123/langchain.git

    # For LangGraph:
    git clone https://github.com/parrot123/langgraph.git
    ```

    ```bash theme={null}
    # Inside your repo, install dependencies
    uv sync --all-groups
    ```

    You will need to install [`uv`](https://docs.astral.sh/uv/) if you haven't previously.
  </Step>

  <Step title="Create a branch">
    ```bash theme={null}
    git checkout -b your-username/short-bugfix-name
    ```
  </Step>

  <Step title="Make your changes">
    Fix the bug while following our [code quality standards](#code-quality-standards)
  </Step>

  <Step title="Add tests">
    Include [unit tests](#test-writing-guidelines) that fail without your fix. This allows us to verify the bug is resolved and prevents regressions
  </Step>

  <Step title="Run tests">
    Ensure all tests pass locally before submitting your PR

    ```bash theme={null}
    make lint
    make test

    # For bugfixes involving integrations, also run:
    make integration_tests
    ```
  </Step>

  <Step title="Submit a pull request">
    Follow the PR template provided. If applicable, reference the issue you're fixing using a [closing keyword](https://docs.github.com/en/issues/tracking-your-work-with-issues/using-issues/linking-a-pull-request-to-an-issue#linking-a-pull-request-to-an-issue-using-a-keyword) (e.g. `Fixes #123`).
  </Step>
</Steps>

### Full development setup

For ongoing development or larger contributions:

<Steps>
  <Step title="Development environment">
    Set up your environment following our [setup guide](#development-environment) below
  </Step>

  <Step title="Repository structure">
    Understand the [repository structure](#repository-structure) and package organization
  </Step>

  <Step title="Development workflow">
    Learn our [development workflow](#development-workflow) including testing and linting
  </Step>

  <Step title="Contribution guidelines">
    Review our [contribution guidelines](#contribution-guidelines) for features, bugfixes, and integrations
  </Step>
</Steps>

### Development environment

<Warning>
  Our Python projects use [`uv`](https://docs.astral.sh/uv/getting-started/installation/) for dependency management. Make sure you have the latest version installed.
</Warning>

Set up a development environment for the package(s) you're working on.

<Tabs>
  <Tab title="LangChain" icon="link">
    <AccordionGroup>
      <Accordion title="Core abstractions">
        For changes to `langchain-core`:

        ```bash theme={null}
        cd libs/core
        uv sync --all-groups
        make test  # Ensure tests pass before starting development
        ```
      </Accordion>

      <Accordion title="Main package">
        For changes to `langchain`:

        ```bash theme={null}
        cd libs/langchain
        uv sync --all-groups
        make test  # Ensure tests pass before starting development
        ```
      </Accordion>

      <Accordion title="Partner packages">
        For changes to [partner integrations](/oss/python/integrations/providers/overview):

        ```bash theme={null}
        cd libs/partners/langchain-{partner}
        uv sync --all-groups
        make test  # Ensure tests pass before starting development
        ```
      </Accordion>

      <Accordion title="Community packages">
        For changes to community integrations (located in a [separate repo](https://github.com/langchain-ai/langchain-community)):

        ```bash theme={null}
        cd libs/community/langchain_community/path/to/integration
        uv sync --all-groups
        make test  # Ensure tests pass before starting development
        ```
      </Accordion>
    </AccordionGroup>
  </Tab>

  <Tab title="LangGraph" icon="circle-nodes">
    WIP - coming soon! In the meantime, follow instructions for LangChain.
  </Tab>
</Tabs>

***

## Repository structure

<Tabs>
  <Tab title="LangChain" icon="link">
    LangChain is organized as a monorepo with multiple packages:

    <AccordionGroup>
      <Accordion title="Core packages" defaultOpen>
        * **[`langchain`](https://github.com/langchain-ai/langchain/tree/master/libs/langchain#readme)** (located in `libs/langchain/`): Main package with chains, agents, and retrieval logic
        * **[`langchain-core`](https://github.com/langchain-ai/langchain/tree/master/libs/core#readme)** (located in `libs/core/`): Base interfaces and core abstractions
      </Accordion>

      <Accordion title="Partner packages">
        Located in `libs/partners/`, these are independently versioned packages for specific integrations. For example:

        * **[`langchain-openai`](https://github.com/langchain-ai/langchain/tree/master/libs/partners/openai#readme)**: [OpenAI](/oss/python/integrations/providers/openai) integrations
        * **[`langchain-anthropic`](https://github.com/langchain-ai/langchain/tree/master/libs/partners/anthropic#readme)**: [Anthropic](/oss/python/integrations/providers/anthropic) integrations
        * **[`langchain-google-genai`](https://github.com/langchain-ai/langchain-google/)**: [Google Generative AI](/oss/python/integrations/chat/google_generative_ai) integrations

        Many partner packages are in external repositories. Please check the [list of integrations](/oss/python/integrations/providers/overview) for details.
      </Accordion>

      <Accordion title="Supporting packages">
        * **[`langchain-text-splitters`](https://github.com/langchain-ai/langchain/tree/master/libs/text-splitters#readme)**: Text splitting utilities
        * **[`langchain-standard-tests`](https://github.com/langchain-ai/langchain/tree/master/libs/standard-tests#readme)**: Standard test suites for integrations
        * **[`langchain-cli`](https://github.com/langchain-ai/langchain/tree/master/libs/cli#readme)**: Command line interface
        * **[`langchain-community`](https://github.com/langchain-ai/langchain-community)**: Community maintained integrations (located in a separate repo)
      </Accordion>
    </AccordionGroup>
  </Tab>

  <Tab title="LangGraph" icon="circle-nodes">
    WIP - coming soon! In the meantime, follow instructions for LangChain.
  </Tab>
</Tabs>

***

## Development workflow

### Testing requirements

<Info>
  Directories are relative to the package you're working in.
</Info>

Every code change must include comprehensive tests.

<Steps>
  <Step title="Unit tests">
    **Location**: `tests/unit_tests/`

    **Requirements**:

    * No network calls allowed
    * Test all code paths including edge cases
    * Use mocks for external dependencies

    ```bash theme={null}
    make test
    # Or directly:
    uv run --group test pytest tests/unit_tests
    ```
  </Step>

  <Step title="Integration tests">
    Integration tests require access to external services/ provider APIs (which can cost money) and therefore are not run by default.

    Not every code change will require an integration test, but keep in mind that we'll require/ run integration tests separately as apart of our review process.

    **Location**: `tests/integration_tests/`

    **Requirements**:

    * Test real integrations with external services
    * Use environment variables for API keys
    * Skip gracefully if credentials unavailable

    ```bash theme={null}
    make integration_tests
    ```
  </Step>

  <Step title="Test quality checklist">
    * Tests fail when your code is broken
    * Edge cases and error conditions are tested
    * Proper use of fixtures and mocks
  </Step>
</Steps>

### Code quality standards

Quality requirements:

<Tabs>
  <Tab title="Type hints">
    **Required**: Complete type annotations for all functions

    ```python theme={null}
    def process_documents(
        docs: list[Document],
        processor: DocumentProcessor,
        *,
        batch_size: int = 100
    ) -> ProcessingResult:
        """Process documents in batches.

        Args:
            docs: List of documents to process.
            processor: Document processing instance.
            batch_size: Number of documents per batch.

        Returns:
            Processing results with success/failure counts.
        """
    ```
  </Tab>

  <Tab title="Documentation">
    **Required**: [Google-style docstrings](https://google.github.io/styleguide/pyguide.html) for all public functions

    * Document all parameters and return values
    * Include usage examples for complex functions
    * Document raised exceptions
    * Focus on "why" rather than "what"
  </Tab>

  <Tab title="Code style">
    **Automated**: Formatting and linting via [`ruff`](https://docs.astral.sh/ruff/)

    ```bash theme={null}
    make format  # Apply formatting
    make lint    # Check style and types
    ```

    **Standards**:

    * Descriptive variable names
    * Break up complex functions (aim for fewer than 20 lines)
    * Follow existing patterns in the codebase
  </Tab>
</Tabs>

### Manual formatting and linting

<Note>
  Code formatting and linting are enforced via CI/CD. Run these commands before committing to ensure your code passes checks.
</Note>

Run formatting and linting:

<Steps>
  <Step title="Format code">
    ```bash theme={null}
    make format
    ```
  </Step>

  <Step title="Run linting checks">
    ```bash theme={null}
    make lint
    ```
  </Step>

  <Step title="Verify changes">
    Both commands will show you any formatting or linting issues that need to be addressed before committing.
  </Step>
</Steps>

***

## Contribution guidelines

### Backwards compatibility

<Warning>
  Breaking changes to public APIs are not allowed except for critical security fixes.

  See our [versioning policy](/oss/python/versioning) for details on major version releases.
</Warning>

Maintain compatibility:

<AccordionGroup>
  <Accordion title="Stable interfaces">
    **Always preserve**:

    * Function signatures and parameter names
    * Class interfaces and method names
    * Return value structure and types
    * Import paths for public APIs
  </Accordion>

  <Accordion title="Safe changes">
    **Acceptable modifications**:

    * Adding new optional parameters

    * Adding new methods to classes

    * Improving performance without changing behavior

    * Adding new modules or functions
  </Accordion>

  <Accordion title="Before making changes">
    * **Would this break existing user code?**

    * Check if your target is public

    * If needed, is it exported in `__init__.py`?

    * Are there existing usage patterns in tests?
  </Accordion>
</AccordionGroup>

### Bugfixes

For bugfix contributions:

<Steps>
  <Step title="Reproduce the issue">
    Create a minimal test case that demonstrates the bug. Maintainers and other contributors should be able to run this test and see the failure without additional setup or modification
  </Step>

  <Step title="Write failing tests">
    Add unit tests that would fail without your fix
  </Step>

  <Step title="Implement the fix">
    Make the **minimal change necessary** to resolve the issue
  </Step>

  <Step title="Verify the fix">
    Ensure that tests pass and no regressions are introduced
  </Step>

  <Step title="Document the change">
    Update docstrings if behavior changes, add comments for complex logic
  </Step>
</Steps>

### New features

We aim to keep the bar high for new features. We generally don't accept new core abstractions, changes to infra, changes to dependencies, or new agents/chains from outside contributors without an existing issue that demonstrates an acute need for them.

In general, feature contribution requirements include:

<Steps>
  <Step title="Design discussion">
    Open an issue describing:

    * The problem you're solving
    * Proposed API design
    * Expected usage patterns
  </Step>

  <Step title="Implementation">
    * Follow existing code patterns
    * Include comprehensive tests and documentation
    * Consider security implications
  </Step>

  <Step title="Integration considerations">
    * How does this interact with existing features?
    * Are there performance implications?
    * Does this introduce new dependencies?

    We will reject features that are likely to lead to security vulnerabilities or reports.
  </Step>
</Steps>

### Security guidelines

<Warning>
  Security is paramount. Never introduce vulnerabilities or unsafe patterns.
</Warning>

Security checklist:

<AccordionGroup>
  <Accordion title="Input validation">
    * Validate and sanitize all user inputs
    * Properly escape data in templates and queries
    * Never use `eval()`, `exec()`, or `pickle` on user data, as this can lead to arbitrary code execution vulnerabilities
  </Accordion>

  <Accordion title="Error handling">
    * Use specific exception types
    * Don't expose sensitive information in error messages
    * Implement proper resource cleanup
  </Accordion>

  <Accordion title="Dependencies">
    * Avoid adding hard dependencies
    * Keep optional dependencies minimal
    * Review third-party packages for security issues
  </Accordion>
</AccordionGroup>

***

## Testing and validation

### Running tests locally

Before submitting your PR, ensure you have completed the following steps. Note that the requirements differ slightly between LangChain and LangGraph.

<Tabs>
  <Tab title="LangChain" icon="link">
    <Steps>
      <Step title="Unit tests">
        ```bash theme={null}
        make test
        ```

        All unit tests must pass
      </Step>

      <Step title="Integration tests">
        ```bash theme={null}
        make integration_tests
        ```

        (Run if your changes affect integrations)
      </Step>

      <Step title="Formatting">
        ```bash theme={null}
        make format
        make lint
        ```

        Code must pass all style checks
      </Step>

      <Step title="Type checking">
        ```bash theme={null}
        make type_check
        ```

        All type hints must be valid
      </Step>

      <Step title="PR submission">
        Push your branch and open a pull request. Follow the provided form template. Note related issues using a [closing keyword](https://docs.github.com/en/issues/tracking-your-work-with-issues/using-issues/linking-a-pull-request-to-an-issue#linking-a-pull-request-to-an-issue-using-a-keyword). After submitting, wait, and check to ensure the CI checks pass. If any checks fail, address the issues promptly - maintainers may close PRs that do not pass CI within a reasonable timeframe.
      </Step>
    </Steps>
  </Tab>

  <Tab title="LangGraph" icon="circle-nodes">
    WIP - coming soon! In the meantime, follow instructions for LangChain.
  </Tab>
</Tabs>

### Test writing guidelines

In order to write effective tests, there's a few good practices to follow:

* Use natural language to describe the test in docstrings
* Use descriptive variable names
* Be exhaustive with assertions

<Tabs>
  <Tab title="Unit tests">
    ```python theme={null}
    def test_document_processor_handles_empty_input():
        """Test processor gracefully handles empty document list."""
        processor = DocumentProcessor()

        result = processor.process([])

        assert result.success
        assert result.processed_count == 0
        assert len(result.errors) == 0
    ```
  </Tab>

  <Tab title="Integration tests">
    ```python theme={null}
    @pytest.mark.requires("openai")
    def test_openai_chat_integration():
        """Test OpenAI chat integration with real API."""

        chat = ChatOpenAI()
        response = chat.invoke("Hello")

        assert isinstance(response.content, str)
        assert len(response.content) > 0
    ```
  </Tab>

  <Tab title="Mock usage">
    ```python theme={null}
    def test_retry_mechanism(mocker):
        """Test retry mechanism handles transient failures."""
        mock_client = mocker.Mock()
        mock_client.call.side_effect = [
            ConnectionError("Temporary failure"),
            {"result": "success"}
        ]

        service = APIService(client=mock_client)
        result = service.call_with_retry()

        assert result["result"] == "success"
        assert mock_client.call.call_count == 2
    ```
  </Tab>
</Tabs>

## Getting help

Our goal is to have the most accessible developer setup possible. Should you experience any difficulty getting setup, please ask in the [community slack](https://www.langchain.com/join-community) or open a [forum post](https://forum.langchain.com/).

<Check>
  You're now ready to contribute high-quality code to LangChain!
</Check>

***

<Callout icon="pen-to-square" iconType="regular">
  [Edit the source of this page on GitHub.](https://github.com/langchain-ai/docs/edit/main/src/oss/contributing/code.mdx)
</Callout>

<Tip icon="terminal" iconType="regular">
  [Connect these docs programmatically](/use-these-docs) to Claude, VSCode, and more via MCP for    real-time answers.
</Tip>