Fixing 405 Method Not Allowed with Open WebUI + Continue in VS Code

VS Code  ·  Continue  ·  Open WebUI  ·  Ollama  ·  API

If you are trying to use Open WebUI as an API backend for Continue in VS Code
and you keep seeing errors like:

POST /api/responses HTTP/1.1" 405

or

POST /api/chat/completions/responses HTTP/1.1" 405

this article may save you some time.

The Problem

At first glance it looks like an API key or routing issue. But the real cause is usually this:

Open WebUI supports these endpoints:

• GET /api/models
• POST /api/chat/completions

But Continue, depending on the selected provider, may try to call:

• POST /api/responses
• POST /api/chat/completions/responses

Open WebUI does not handle those endpoints, so the server responds with
405 Method Not Allowed.

Root Cause

The original Continue configuration used provider: openai. With that setting,
newer versions of Continue may switch to the OpenAI Responses API format,
which appends /responses to the request path.

Open WebUI does not implement the Responses API, so every request fails with a
405 before it even reaches the model.

The Fix

Change the provider in your Continue configuration from openai to
lmstudio:

Before

models:
  - name: OpenWebUI
    provider: openai
    model: llama3.1
    apiBase: http://localhost:3000/api
    apiKey: your_api_key

After

models:
  - name: OpenWebUI
    provider: lmstudio
    model: llama3.1
    apiBase: http://localhost:3000/api
    apiKey: your_api_key

Why This Works

The lmstudio provider in Continue uses the classic OpenAI-compatible
chat/completions request format instead of the newer Responses API style.
Open WebUI supports chat/completions, so the requests go through correctly.

Verify Open WebUI is Working

You can test the API directly with curl before touching your Continue config.

List available models:

curl -H "Authorization: Bearer YOUR_API_KEY" \
  http://localhost:3000/api/models

Test a chat completion request:

curl -X POST http://localhost:3000/api/chat/completions \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "llama3.1",
    "messages": [
      { "role": "user", "content": "Hello" }
    ]
  }'

Summary

If Continue in VS Code sends requests to /api/responses or
/api/chat/completions/responses and Open WebUI returns
405 Method Not Allowed, the fix is simple:

# Change this
provider: openai

# To this
provider: lmstudio

This makes Continue use the classic chat completions flow that Open WebUI supports,
instead of the newer Responses API that Open WebUI does not implement.