HTTP 101 — Switching Protocols

1xx Informational

What it means

The server is switching to the protocol the client asked for in the Upgrade header — almost always a WebSocket handshake.

What to do about it

Nothing to fix. If you expected a WebSocket connection and do not see a 101, check that a proxy in front of the app forwards the Upgrade and Connection headers.

Where it sits

101 belongs to the 1xx family: The request was received and the process is continuing. These are rarely seen by application code.

HTTP/1.1 101 Switching Protocols

Checking it yourself

# see the status code and headers only
curl -sI https://example.com/path

# follow redirects and print each hop
curl -sIL -o /dev/null -w "%{http_code} %{url_effective}\n" https://example.com/path

# JavaScript
const r = await fetch(url);
console.log(r.status, r.statusText);

How this code behaves

Returning 101 correctly

# nginx
return 101;

# Express
res.status(101).json({ error: 'Switching Protocols' });

# Go
w.WriteHeader(101)

# Python (Flask)
return jsonify(error='Switching Protocols'), 101;

Frequently asked questions

Other 1xx codes

• 100 Continue
• 103 Early Hints

All HTTP status codes