draw_mermaid_png Mermaid.INK API. Status code: 400

[khteh]

Checked other resources

• I added a very descriptive title to this issue.
• I searched the LangChain documentation with the integrated search.
• I used the GitHub search to find a similar question and didn't find it.
• I am sure that this is a bug in LangChain rather than my code.
• The bug is not resolved by updating to the latest stable version of LangChain (or the specific integration package).

Example Code

graph.get_graph().draw_mermaid_png()

Error Message and Stack Trace (if applicable)

    img_bytes = graph.get_graph().draw_mermaid_png()
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/khteh/.local/lib/python3.12/site-packages/langchain_core/runnables/graph.py", line 631, in draw_mermaid_png
    return draw_mermaid_png(
           ^^^^^^^^^^^^^^^^^
  File "/home/khteh/.local/lib/python3.12/site-packages/langchain_core/runnables/graph_mermaid.py", line 250, in draw_mermaid_png
    img_bytes = _render_mermaid_using_api(
                ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/khteh/.local/lib/python3.12/site-packages/langchain_core/runnables/graph_mermaid.py", line 380, in _render_mermaid_using_api
    raise ValueError(msg)
ValueError: Failed to render the graph using the Mermaid.INK API. Status code: 400.
Error in sys.excepthook:
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/apport_python_hook.py", line 228, in partial_apport_excepthook
    return apport_excepthook(binary, exc_type, exc_obj, exc_tb)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/apport_python_hook.py", line 114, in apport_excepthook
    report["ExecutableTimestamp"] = str(int(os.stat(binary).st_mtime))
                                            ^^^^^^^^^^^^^^^

Description

What's up with the get_graph().draw_mermaid_png()? It throws the 400 error from mermaid API.

System Info

System Information
------------------
> OS:  Linux
> OS Version:  #19-Ubuntu SMP PREEMPT_DYNAMIC Wed Feb 12 21:43:43 UTC 2025
> Python Version:  3.12.7 (main, Feb  4 2025, 14:46:03) [GCC 14.2.0]

Package Information
-------------------
> langchain_core: 0.3.45
> langchain: 0.3.20
> langchain_community: 0.3.19
> langsmith: 0.3.15
> langchain_google_genai: 2.1.0
> langchain_google_vertexai: 2.0.9
> langchain_openai: 0.3.8
> langchain_text_splitters: 0.3.6
> langgraph_api: 0.0.28
> langgraph_cli: 0.1.75
> langgraph_license: Installed. No version info available.
> langgraph_sdk: 0.1.57
> langgraph_storage: Installed. No version info available.

Optional packages not installed
-------------------------------
> langserve

Other Dependencies
------------------
> aiohttp<4.0.0,>=3.8.3: Installed. No version info available.
> anthropic[vertexai]: Installed. No version info available.
> async-timeout<5.0.0,>=4.0.0;: Installed. No version info available.
> click: 8.1.8
> cryptography: 43.0.3
> dataclasses-json<0.7,>=0.5.7: Installed. No version info available.
> filetype: 1.2.0
> google-ai-generativelanguage: 0.6.16
> google-cloud-aiplatform: 1.84.0
> google-cloud-storage: 2.19.0
> httpx: 0.27.2
> httpx-sse: 0.4.0
> httpx-sse<1.0.0,>=0.4.0: Installed. No version info available.
> jsonpatch<2.0,>=1.33: Installed. No version info available.
> jsonschema-rs: 0.20.0
> langchain-anthropic;: Installed. No version info available.
> langchain-aws;: Installed. No version info available.
> langchain-cohere;: Installed. No version info available.
> langchain-community;: Installed. No version info available.
> langchain-core<1.0.0,>=0.3.34: Installed. No version info available.
> langchain-core<1.0.0,>=0.3.41: Installed. No version info available.
> langchain-core<1.0.0,>=0.3.42: Installed. No version info available.
> langchain-deepseek;: Installed. No version info available.
> langchain-fireworks;: Installed. No version info available.
> langchain-google-genai;: Installed. No version info available.
> langchain-google-vertexai;: Installed. No version info available.
> langchain-groq;: Installed. No version info available.
> langchain-huggingface;: Installed. No version info available.
> langchain-mistralai: Installed. No version info available.
> langchain-mistralai;: Installed. No version info available.
> langchain-ollama;: Installed. No version info available.
> langchain-openai;: Installed. No version info available.
> langchain-text-splitters<1.0.0,>=0.3.6: Installed. No version info available.
> langchain-together;: Installed. No version info available.
> langchain-xai;: Installed. No version info available.
> langchain<1.0.0,>=0.3.20: Installed. No version info available.
> langgraph: 0.3.11
> langgraph-checkpoint: 2.0.20
> langsmith-pyo3: Installed. No version info available.
> langsmith<0.4,>=0.1.125: Installed. No version info available.
> langsmith<0.4,>=0.1.17: Installed. No version info available.
> numpy<3,>=1.26.2: Installed. No version info available.
> openai-agents: Installed. No version info available.
> openai<2.0.0,>=1.58.1: Installed. No version info available.
> orjson: 3.10.15
> packaging: 24.2
> packaging<25,>=23.2: Installed. No version info available.
> pydantic: 2.9.2
> pydantic-settings<3.0.0,>=2.4.0: Installed. No version info available.
> pydantic<3.0.0,>=2.5.2;: Installed. No version info available.
> pydantic<3.0.0,>=2.7.4: Installed. No version info available.
> pydantic<3.0.0,>=2.7.4;: Installed. No version info available.
> pyjwt: 2.10.1
> pytest: 8.3.2
> python-dotenv: 1.0.1
> PyYAML>=5.3: Installed. No version info available.
> requests: 2.32.3
> requests-toolbelt: 1.0.0
> requests<3,>=2: Installed. No version info available.
> rich: 13.9.4
> SQLAlchemy<3,>=1.4: Installed. No version info available.
> sse-starlette: 2.1.3
> starlette: 0.46.1
> structlog: 25.1.0
> tenacity: 9.0.0
> tenacity!=8.4.0,<10,>=8.1.0: Installed. No version info available.
> tenacity!=8.4.0,<10.0.0,>=8.1.0: Installed. No version info available.
> tiktoken<1,>=0.7: Installed. No version info available.
> typing-extensions>=4.7: Installed. No version info available.
> uvicorn: 0.34.0
> watchfiles: 1.0.4
> zstandard: 0.23.0

[lovelyscientist]

Try this (from https://langchain-ai.github.io/langgraph/how-tos/visualization/#using-mermaidink)

from IPython.display import Image, display
from langchain_core.runnables.graph import CurveStyle, MermaidDrawMethod, NodeStyles

display(
    Image(
        app.get_graph().draw_mermaid_png(
            draw_method=MermaidDrawMethod.API,
        )
    )
)

[khteh]

https://stackoverflow.com/questions/79493962/ipython-display-does-not-show-any-image-at-all-but-ipython-core-display-image-o/79499656?noredirect=1#comment140203191_79499656

[khteh]

I don't face this issue nowadays.