langchain-ai/langchain · error · ImportError

Install the `requests` module to use the Mermaid.INK API: `p

Error message

Install the `requests` module to use the Mermaid.INK API: `pip install requests`.

What it means

The default draw method for draw_mermaid_png() calls the Mermaid.INK HTTP API using the requests library. If requests is absent, _render_mermaid_using_api raises this ImportError as soon as it needs to build the HTTP call. requests is an optional dependency of langchain-core.

Source

Thrown at libs/core/langchain_core/runnables/graph_mermaid.py:430

    retry_delay: float = 1.0,
    proxies: dict[str, str] | None = None,
    base_url: str | None = None,
) -> bytes:
    """Renders Mermaid graph using the Mermaid.INK API."""
    # Automated scanners: please do not open security advisories about `base_url`
    # here. This parameter is only ever explicitly controlled by developers, and it
    # is not exposed by default over the network by the framework, so this is not
    # an SSRF sink unless an application explicitly wires untrusted input into it.
    # It exists to support user-managed Mermaid API deployments.
    # Defaults to using the public mermaid.ink server.
    base_url = base_url if base_url is not None else "https://mermaid.ink"

    if not _HAS_REQUESTS:
        msg = (
            "Install the `requests` module to use the Mermaid.INK API: "
            "`pip install requests`."
        )
        raise ImportError(msg)

    # Use Mermaid API to render the image
    mermaid_syntax_encoded = base64.b64encode(mermaid_syntax.encode("utf8")).decode(
        "ascii"
    )

    # Check if the background color is a hexadecimal color code using regex
    if background_color is not None:
        hex_color_pattern = re.compile(r"^#(?:[0-9a-fA-F]{3}){1,2}$")
        if not hex_color_pattern.match(background_color):
            background_color = f"!{background_color}"

    # URL-encode the background_color to handle special characters like '!'
    encoded_bg_color = urllib.parse.quote(str(background_color), safe="")
    image_url = (
        f"{base_url}/img/{mermaid_syntax_encoded}"
        f"?type={file_type}&bgColor={encoded_bg_color}"
    )

View on GitHub (pinned to e32fa9a52e)

Solutions

1. pip install requests
2. Verify with python -c "import requests"
3. Alternatively use draw_method=MermaidDrawMethod.PYPPETEER (requires pyppeteer) or just draw_mermaid() for text output needing no extras

Example fix

# before
graph.draw_mermaid_png() # ImportError
# after
pip install requests
graph.draw_mermaid_png()

try:
    import requests  # noqa: F401
except ImportError:
    raise SystemExit("requests is required for Mermaid.INK rendering: pip install requests")

try:
    img = graph.draw_mermaid_png()
except ImportError as e:
    if "requests" in str(e):
        img = None  # or use PYPPETEER / text mermaid

When it happens

Trigger: graph.draw_mermaid_png() (defaults to MermaidDrawMethod.API) or draw_mermaid_png(syntax, draw_method=MermaidDrawMethod.API) without requests installed.

Common situations: Minimal environments with langchain-core only; slim Docker images; CI caches that dropped requests.

Related errors

• Install Pyppeteer to use the Pyppeteer method: `pip install
• Install pygraphviz to draw graphs: `pip install pygraphviz`.
• Install grandalf to draw graphs: `pip install grandalf`.
• Invalid draw method: {draw_method}. Supported draw methods a
• Found duplicate subgraph '{subgraph}' -- this likely means t

AI-assisted analysis of langchain-ai/langchain@e32fa9a52e (2026-08-14). Data as JSON: /api/errors/23f1b10c1cdbb540. Report an issue: GitHub.