WebSocket

1010 Mandatory Extension

The client is terminating the connection because the server did not negotiate one or more expected extensions in the handshake response.

On this page

When You See This Code

The client requested a required WebSocket extension (e.g., permessage-deflate compression) during the handshake, but the server did not include it in its response.

How to Fix

Enable the required extension on the server, or update the client to make the extension optional. Check the Sec-WebSocket-Extensions header in the handshake response.

Specification

View RFC / Specification →

Compare With

1000 Normal Closure 1001 Going Away 1002 Protocol Error 1003 Unsupported Data 1005 No Status Received 1006 Abnormal Closure 1007 Invalid Payload Data 1008 Policy Violation 1009 Message Too Big 1011 Internal Error 1012 Service Restart 1013 Try Again Later

Guides

Debugging CORS Errors: A Developer's Guide Debugging & Troubleshooting

Debugging WebSocket Disconnections Debugging & Troubleshooting

WebSocket Close Codes: Why Your Connection Dropped Real-Time Protocols

WebSocket Authentication Patterns Real-Time Protocols

WebSocket vs Server-Sent Events: Choosing the Right Protocol Real-Time Protocols

WebRTC Signaling with SIP and WebSocket Real-Time Protocols

gRPC Streaming vs REST Polling: Real-Time Data Delivery Real-Time Protocols

MQTT Protocol: Lightweight Messaging for IoT and Real-Time Systems Real-Time Protocols

WebSocket Performance Tuning Performance & Optimization

RFC 6455: WebSocket Protocol Deep Dive Protocol Deep Dives

RFC 9114: HTTP/3 Protocol Deep Dive Protocol Deep Dives

QUIC Protocol: The Transport Layer Behind HTTP/3 Protocol Deep Dives

TLS 1.3: Faster, Simpler, More Secure Protocol Deep Dives

Migrating from WebSocket to Server-Sent Events Migration & Upgrades

Reverse Proxy Configuration: Nginx, Caddy, and HAProxy Production Infrastructure

Connection Draining: Graceful Shutdown Without Dropping Requests Production Infrastructure

API Gateway Patterns: Architecture and Use Cases API Gateway Patterns

API Gateway Request Routing: Path, Header, and Content-Based API Gateway Patterns

Request and Response Transformation at the API Gateway API Gateway Patterns

CORS Handling at the API Gateway API Gateway Patterns

API Security Testing: OWASP ZAP, Burp Suite, and Automated Scanning Testing & Mocking

Glossary

GraphQL CORS (Cross-Origin Resource Sharing) Port Number Latency NAT (Network Address Translation) Socket Bandwidth Backpressure Thundering Herd Request-Response Model RFC (Request for Comments) Protocol Upgrade Multiplexing Message Framing Full-Duplex WebSocket Frame WebRTC (Web Real-Time Communication) Signaling ICE Candidate WebSocket Subprotocol WebSocket Ping/Pong WebSocket Close Code STUN (Session Traversal Utilities for NAT) TURN (Traversal Using Relays around NAT) SDP (Session Description Protocol) MQTT (Message Queuing Telemetry Transport) STOMP (Simple Text Oriented Messaging Protocol) RTP (Real-time Transport Protocol) Codec Negotiation

Frequently Asked Questions

What is WebSocket 1010 Mandatory Extension?

The client is terminating the connection because the server did not negotiate one or more expected extensions in the handshake response.

When do you see WebSocket 1010 Mandatory Extension?

The client requested a required WebSocket extension (e.g., permessage-deflate compression) during the handshake, but the server did not include it in its response.

How to fix WebSocket 1010 Mandatory Extension?

Enable the required extension on the server, or update the client to make the extension optional. Check the Sec-WebSocket-Extensions header in the handshake response.