# aiohttp.client_exceptions.WSServerHandshakeError: Invalid websocket handshake

- **ID:** `python/aiohttp-websocket-handshake-error`
- **Domain:** python
- **Category:** network_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

The server does not support WebSocket protocol or the handshake response is malformed.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| 3.10 | active | — | — |
| 3.11 | active | — | — |

## Workarounds

1. **Verify server WebSocket endpoint and use correct URL scheme (ws:// or wss://)** (90% success)
   ```
   async with session.ws_connect('wss://example.com/ws') as ws:
    async for msg in ws:
   ```
2. **Fall back to HTTP long polling if WebSocket fails** (80% success)
   ```
   try:
    async with session.ws_connect(url) as ws:
        # use websocket
except aiohttp.WSServerHandshakeError:
    # fallback to polling
   ```

## Dead Ends

- **Using a different WebSocket library without checking server compatibility** — The server itself may not support WebSocket, so changing the client library won't help. (60% fail)
- **Adding custom headers to the handshake request** — If the server rejects WebSocket at the protocol level, custom headers won't fix it. (50% fail)