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langgraph-cli dev server starts but returns 404 on root and /docs, Studio fails to connect #376

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opened 2026-02-15 18:16:20 -05:00 by yindo · 1 comment
yindo commented 2026-02-15 18:16:20 -05:00
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Originally created by @nicobytes on GitHub (Nov 18, 2025).

Checked other resources

  • I added a very descriptive title to this issue.
  • I searched the LangGraph.js 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 LangGraph.js rather than my code.
  • The bug is not resolved by updating to the latest stable version of LangGraph (or the specific integration package).

Example Code

This is my graph:

import {
  MessagesAnnotation,
  StateGraph,
  START,
  END,
} from '@langchain/langgraph';

const mockLlm = (_: typeof MessagesAnnotation.State) => {
  return { messages: [{ role: 'ai', content: 'hello world' }] };
};

export const graph = new StateGraph(MessagesAnnotation)
  .addNode('mock_llm', mockLlm)
  .addEdge(START, 'mock_llm')
  .addEdge('mock_llm', END)
  .compile();

Error Message and Stack Trace (if applicable)

Image

Description

I am trying to run a simple LangGraph application using the CLI development server. The terminal indicates that the server has started successfully and registered my graph. However, when I try to access the API documentation (/docs) or connect via LangGraph Studio, I get connection errors and 404 responses.

Image

Steps to Reproduce:

  1. Define a simple graph
  2. Run the dev server using npx @langchain/langgraph-cli dev (or via npm script).
  3. The terminal shows Server running at ::1:2024.
  4. Navigate to http://localhost:2024/docs or open the LangGraph Studio URL provided in the terminal.

System Info

Node version: v24.11.1
Operating system: darwin arm64
Package manager: npm
Package manager version: N/A

@langchain/core -> @1.0.5, , @"1.0.5", @"^1.0.5", @"^1.0.1", @"^0.3.59, @"^1.0.0"
langsmith -> @0.3.79, , @"~0.3.74", @"^0.3.33", @"^0.3.64"
zod -> @4.1.12, , @"^4.1.12", @"^3.25.76, @"^3.25, @"^3.25.32, @3.25.76, @"^3.19.1"
@langchain/langgraph-checkpoint-postgres -> @1.0.0, , @"1.0.0"
@langchain/langgraph-checkpoint -> @1.0.0, , @"^1.0.0", @"~0.0.16
@langchain/langgraph-cli -> @1.0.3, , @"1.0.3"
@langchain/langgraph-api -> @1.0.3, , @"1.0.3"
@langchain/langgraph-sdk -> @1.0.0, , @"~1.0.0", @"~0.0.16
@langchain/langgraph-ui -> @1.0.3, , @"1.0.3"
@langchain/langgraph -> @1.0.2, , @"1.0.2", @"^1.0.0", @"^0.2.57
@langchain/openai -> @1.1.2, , @"1.1.2"
langchain -> @1.0.5, , @"1.0.5"

Originally created by @nicobytes on GitHub (Nov 18, 2025). ### Checked other resources - [x] I added a very descriptive title to this issue. - [x] I searched the LangGraph.js documentation with the integrated search. - [x] I used the GitHub search to find a similar question and didn't find it. - [x] I am sure that this is a bug in LangGraph.js rather than my code. - [x] The bug is not resolved by updating to the latest stable version of LangGraph (or the specific integration package). ### Example Code This is my graph: ``` import { MessagesAnnotation, StateGraph, START, END, } from '@langchain/langgraph'; const mockLlm = (_: typeof MessagesAnnotation.State) => { return { messages: [{ role: 'ai', content: 'hello world' }] }; }; export const graph = new StateGraph(MessagesAnnotation) .addNode('mock_llm', mockLlm) .addEdge(START, 'mock_llm') .addEdge('mock_llm', END) .compile(); ``` ### Error Message and Stack Trace (if applicable) <img width="537" height="441" alt="Image" src="https://github.com/user-attachments/assets/0fe8d3df-5d91-40ee-b1ba-566d082e1030" /> ### Description I am trying to run a simple LangGraph application using the CLI development server. The terminal indicates that the server has started successfully and registered my graph. However, when I try to access the API documentation (/docs) or connect via LangGraph Studio, I get connection errors and 404 responses. <img width="919" height="547" alt="Image" src="https://github.com/user-attachments/assets/4e08a495-6ffd-4ff0-b0ce-351d6a403a67" /> Steps to Reproduce: 1. Define a simple graph 2. Run the dev server using npx @langchain/langgraph-cli dev (or via npm script). 3. The terminal shows Server running at ::1:2024. 4. Navigate to http://localhost:2024/docs or open the LangGraph Studio URL provided in the terminal. ### System Info Node version: v24.11.1 Operating system: darwin arm64 Package manager: npm Package manager version: N/A -------------------- @langchain/core -> @1.0.5, , @"1.0.5", @"^1.0.5", @"^1.0.1", @"^0.3.59, @"^1.0.0" langsmith -> @0.3.79, , @"~0.3.74", @"^0.3.33", @"^0.3.64" zod -> @4.1.12, , @"^4.1.12", @"^3.25.76, @"^3.25, @"^3.25.32, @3.25.76, @"^3.19.1" @langchain/langgraph-checkpoint-postgres -> @1.0.0, , @"1.0.0" @langchain/langgraph-checkpoint -> @1.0.0, , @"^1.0.0", @"~0.0.16 @langchain/langgraph-cli -> @1.0.3, , @"1.0.3" @langchain/langgraph-api -> @1.0.3, , @"1.0.3" @langchain/langgraph-sdk -> @1.0.0, , @"~1.0.0", @"~0.0.16 @langchain/langgraph-ui -> @1.0.3, , @"1.0.3" @langchain/langgraph -> @1.0.2, , @"1.0.2", @"^1.0.0", @"^0.2.57 @langchain/openai -> @1.1.2, , @"1.1.2" langchain -> @1.0.5, , @"1.0.5"
yindo commented 2026-02-15 18:16:20 -05:00
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@marcelopottier commented on GitHub (Jan 26, 2026):

Hey, nico!

I don't know if you found the solution for this issue already. But, I was having the same problem and the solution for me was enabling some option in studio web page.

Check if the you can find "Local network access" and change from "Ask (default)" or "Block" to "Allow". Like the image below...

Image
@marcelopottier commented on GitHub (Jan 26, 2026): Hey, nico! I don't know if you found the solution for this issue already. But, I was having the same problem and the solution for me was enabling some option in studio web page. Check if the you can find "Local network access" and change from "Ask (default)" or "Block" to "Allow". Like the image below... <img width="783" height="676" alt="Image" src="https://github.com/user-attachments/assets/a6939040-66ab-4f0b-875d-8c7b8748e08a" />
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Reference: langchain-ai/langgraphjs#376
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