ComfyUI "Failed to Fetch": Which Connection Is Failing?

Failed to fetch does not identify the real ComfyUI problem.

It only means that the browser sent a request and did not receive a usable response. The failed request may belong to ComfyUI itself, ComfyUI Manager, ComfyRegistry, workflow draft storage, server logs, or a WebSocket connection.

Do not reinstall ComfyUI yet.

First identify what the interface was trying to fetch.

Choose the right branch

First determine whether the backend is still alive

Look at the terminal, PowerShell window, command prompt, launcher log, or Desktop log that started ComfyUI.

A healthy backend normally continues running and shows the address used by the frontend.

For example:

To see the GUI go to: http://127.0.0.1:8188

Use the host and port shown in your own log. Do not assume every installation uses port 8188.

The backend is probably still running if

• The terminal has not closed.
• There is no traceback at the bottom of the log.
• Opening the logged address loads ComfyUI.
• Queue and history requests still work.
• Only one Manager or frontend feature fails.

In this case, the problem is probably limited to one request, browser path, network layer, or extension.

The backend may have stopped if

• The terminal closed.
• A Python traceback appeared immediately before the fetch error.
• The original address no longer opens.
• Every part of the interface fails at the same time.
• A restart uses a different port.

A browser-side Failed to fetch message cannot explain why the backend stopped. Read the last terminal error instead, then use ComfyUI Startup Failed if the server no longer starts.

If only server logs fail to load

When the main ComfyUI interface still works but the server-log panel shows Failed to fetch, do not treat it as a complete ComfyUI outage.

The failure may be limited to:

• the server-log endpoint;
• a frontend and backend version mismatch;
• a stale browser bundle;
• a reverse proxy that does not forward the endpoint;
• a Desktop or packaged environment using a different backend route.

Continue with ComfyUI "Failed to Fetch Server Logs". That page handles the endpoint-specific checks. This parent page is only the router.

If Manager cannot load the custom-node list

A Manager failure does not automatically mean that ComfyUI itself is broken.

ComfyUI Manager may need to reach:

• ComfyRegistry;
• GitHub;
• raw GitHub content;
• a cached node list;
• Manager-specific API endpoints.

Check whether normal ComfyUI generation still works.

If only Manager shows messages such as:

Failed to get custom node list

or:

Failed to find the following ComfyRegistry list

continue with ComfyUI-Manager "Failed to Get Custom Node List".

Do not reinstall every custom node before checking the Manager request itself.

If the interface keeps saying Reconnecting

Reconnecting usually means the frontend lost its live connection to the ComfyUI backend.

This is different from one optional Manager request failing.

Possible areas include:

• the ComfyUI process stopping;
• the backend restarting;
• a WebSocket connection being blocked;
• a reverse proxy not forwarding WebSocket traffic;
• the browser using an old port;
• the computer sleeping or changing networks.

Continue with ComfyUI Reconnecting Error.

If the page reconnects successfully and generation still works, do not perform a full dependency reinstall.

If saving the workflow draft fails

A workflow draft failure is more urgent because the graph may currently exist only in the open browser tab.

The safest first action is to use the currently available Save or Export option before refreshing or closing the tab.

The error means the automatic draft-save request failed. It does not necessarily mean the workflow has already disappeared.

Avoid these actions until you have saved or exported what you can:

• refreshing the page;
• closing the browser tab;
• clearing browser site data;
• restarting ComfyUI without first preserving the graph.

Continue with ComfyUI "Failed to Save Workflow Draft".

For normal workflow backup and recovery, not an active error, use the workflow-saving sections in ComfyUI "Failed to Save Workflow Draft" until the standalone workflow-saving tutorial is published.

If a VPN, proxy, firewall, or company network is involved

A request may reach the main ComfyUI page while another endpoint is blocked.

This is common when:

• ComfyUI is accessed through a reverse proxy;
• a browser proxy extension is enabled;
• a VPN changes local routing;
• security software filters localhost traffic;
• a company network blocks GitHub or Registry requests;
• HTTP and HTTPS content are mixed;
• WebSocket forwarding is missing.

Do not disable every security control as the first fix.

Instead, compare:

1. The same action with the VPN or proxy temporarily bypassed.
2. The main ComfyUI page versus the specific feature that fails.
3. Local access versus reverse-proxy access.
4. A normal browser window versus an extension-free private window.

If the problem disappears only after bypassing one network layer, inspect that layer's rules rather than changing the ComfyUI Python environment.

If you use ComfyUI Desktop

ComfyUI Desktop manages parts of the startup environment differently from a manual or Portable installation.

Do not assume:

• its backend always uses the default port;
• its Python environment is the same as system Python;
• a Portable repair command applies to Desktop;
• the browser address remains unchanged after a restart.

Check the Desktop app or its logs for:

• the active backend address;
• startup failure messages;
• frontend/backend version information;
• whether the backend restarted;
• extension loading errors.

Because Desktop-managed paths and recovery actions can change between releases, use the current app UI or official Desktop documentation before applying a command written for a manual or Portable install.

Use browser developer tools to identify the failed request

When the message is still too vague, the browser can show which request failed.

In Chromium-based browsers:

1. Open Developer Tools.
2. Select Network.
3. Repeat the action that triggers Failed to fetch.
4. Look for the failed request.
5. Record its request name, URL, status, and error.

Common patterns:

Do not publish cookies, authorization headers, private workflow data, local usernames, or API keys when sharing a Network-panel screenshot.

What not to do first

Avoid using these as universal fixes:

• reinstalling ComfyUI;
• deleting every custom node;
• upgrading every Python package;
• running pip install in system Python;
• clearing all browser data before exporting the workflow;
• disabling the firewall permanently;
• changing CUDA or PyTorch because one HTTP request failed;
• assuming every installation must use port 8188.

Those actions may create a second problem without identifying the failed request.

How to verify the problem is fixed

Repeat the exact action that originally produced Failed to fetch.

A successful repair should meet the relevant condition:

• the same panel now loads;
• Manager retrieves its list;
• the page stops reconnecting;
• the workflow draft saves;
• the failed request returns a usable response;
• ComfyUI remains available at the address shown in its startup log.

Do not use "the page opened once" as the only acceptance check if the original failure involved a specific Manager, log, draft, or WebSocket request.

How Wonderful Launcher fits

Wonderful Launcher is most useful after you know which layer failed. It can help you keep ComfyUI environments, model folders, and custom node setup more organized, so you do not have to treat every connection message as a full reinstall.

If the failed request points to missing models, broken custom nodes, or a damaged local environment, use the specific guide above first, then download Wonderful Launcher if you want a cleaner way to manage recovery work.

Related ComfyUI connection errors

• Failed to Fetch Server Logs
• Failed to Get Custom Node List
• ComfyUI Reconnecting Error
• Failed to Save Workflow Draft
• ComfyUI Startup Failed
• ComfyUI Workflow Has Missing Nodes

Source References

• Official ComfyUI troubleshooting overview
• Official custom node troubleshooting guide
• Official ComfyUI Manager pack management guide