What does close code 1006 mean?

1006 Abnormal Closure indicates the connection was lost without a Close frame, such as a dropped TCP connection or network failure. It is reserved and set internally by the library, so you must never send 1006 yourself.

Which close codes can I use for my own application?

The 4000–4999 range is reserved for private application use, so you can define those codes freely. The 3000–3999 range is for codes registered with IANA by libraries and frameworks.

What is the normal way to close a WebSocket?

Send a Close frame with code 1000 Normal Closure to signal that the connection completed successfully. The peer should respond with its own Close frame and then the TCP connection is torn down.

Why can't I read codes 1005 and 1015?

1005 No Status Received and 1015 TLS Handshake are reserved values set internally by the library to describe the close. They must never appear in an actual Close frame sent over the wire.

Do close codes include a human-readable reason?

Yes. A Close frame can carry a 2-byte status code plus an optional UTF-8 reason string up to 123 bytes. The reason is for logging and debugging and should not be parsed by machines.

What is the WebSocket Close Codes?

Reference for WebSocket connection close codes defined by RFC 6455 and the IANA registry, with the application-reserved 3000–4999 ranges and which endpoint sends each code. It runs free in your browser on Gera Tools, with nothing uploaded.

WebSocket Close Codes

Name: WebSocket Close Codes
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

WebSocket close codes

When a WebSocket connection ends, the closing endpoint can send a Close frame containing a numeric status code and an optional reason string. These codes — defined in RFC 6455 and extended through the IANA registry — explain why the socket closed: a clean shutdown, a protocol error, an oversized message, or an application-specific reason of your own. Some codes are reserved and set only by the library (you must never send them yourself), and whole ranges are carved out for application use. Search the reference above by number or keyword.

How it works

A Close frame carries a 2-byte big-endian status code followed by an optional UTF-8 reason of up to 123 bytes. The protocol-defined codes live in 1000–2999. Within that, 1000 is a clean close, 1001–1011 cover protocol, data, policy, and server errors, and a few values (1005, 1006, 1015) are reserved — they describe what happened but must never be transmitted in a frame. The 3000–3999 range is for codes registered with IANA by libraries and frameworks, and 4000–4999 is entirely private: your application can assign its own meanings there without coordinating with anyone. Codes below 1000 are never used.

Quick reference: the key ranges

Range	Owner	What it means
1000	Protocol	Normal, intentional close
1001	Protocol	Endpoint going away (server restart, tab closed)
1002	Protocol	Protocol error
1003	Protocol	Unacceptable data type (e.g. binary when only text expected)
1005	Reserved	No status code was present (library only, never sent)
1006	Reserved	Abnormal closure — no Close frame received (library only)
1007	Protocol	Invalid UTF-8 in a text frame
1008	Protocol	Policy violation
1009	Protocol	Message too large
1011	Protocol	Unexpected server error
1015	Reserved	TLS handshake failure (library only, never sent)
3000–3999	IANA registered	Library and framework codes (e.g. Stomp, MQTT adapters)
4000–4999	Application private	Your own application-specific reasons

Common debugging scenarios

Client sees 1006 — what happened? The TCP connection dropped without a Close frame. Common causes: network interruption, load balancer timeout, server process killed abruptly. It is a connectivity event, not an application error. Add exponential backoff reconnect logic and log the reconnect attempt.

Server wants to reject an unauthenticated connection. Send a Close frame with code 4001 (or whatever your app defines for “unauthenticated”) immediately after the HTTP upgrade handshake completes. Do not leave the socket open and silently ignore messages.

Library or framework close codes in the 3000s. These are IANA-registered by the authors of specific toolkits (e.g. a message-queue bridge or a multiplexing layer). If you see an unfamiliar 3xxx code, check the library’s documentation rather than the RFC.

Tips and examples

Close cleanly with 1000 Normal Closure when work is done, and let the peer echo a Close frame before the TCP teardown.
Treat 1006 as a connectivity signal, not an application error — it means the socket dropped without a Close frame, so reconnect with backoff.
Reserve a 4000–4999 code for each of your own shutdown reasons (e.g. 4001 = session expired, 4002 = kicked by admin) and document them for clients.
Keep reason strings short and human-readable for logs; never rely on parsing them programmatically since they are not standardized.
Codes 1005, 1006, and 1015 must never appear in an actual Close frame you send — they are set internally by the library to describe the event after the fact.