HTTP 101 Switching Protocols — Meaning, Causes & How to Fix

Code

101

Name

Switching Protocols

Class

1xx Informational

Specification

RFC 9110 §15.2.2

Cacheable by default

Not applicable (interim response)

What HTTP 101 means

101 Switching Protocols means the server accepts the client’s Upgrade request and, right after this response, the connection speaks a different protocol. Its most common use today is opening a WebSocket connection from an HTTP/1.1 request.

Common causes

• A browser or client opened a WebSocket (Upgrade: websocket).
• A client requested an upgrade to another protocol on the same connection.

How to fix it

For site owners

• If WebSockets fail behind a reverse proxy, forward the Upgrade and Connection headers (in nginx: proxy_http_version 1.1 plus both headers).
• Make sure load balancers allow long-lived connections.

For visitors & developers

• A 101 is success for a WebSocket handshake — anything else (often 400, 403 or 426) means the upgrade was refused.

SEO impact

No SEO impact. Crawlers do not open WebSocket connections; pages should not depend on them for indexable content.

Example 101 response

HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=

Related status codes

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