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WebSocket Close Code Reference / Lookup

Network

Look up what a WebSocket close code means, per the RFC 6455 close code definitions and the IANA WebSocket Close Code Number Registry's reserved ranges, or browse every well-known code

Every WebSocket close frame carries a 16-bit close code, and remembering what each one means while debugging a dropped connection is not something most developers have memorized. This tool looks up a code and returns its name, plain-English meaning, and which reserved range it falls in: 1000 through 1015 are the specific well-known codes defined directly by RFC 6455, 3000 through 3999 are reserved for libraries and frameworks to register with IANA, and 4000 through 4999 are reserved for private use between a specific client and server with no fixed meaning. It also flags the handful of codes, like 1005 and 1006, that libraries use internally to represent a close with no code or an abnormal disconnect, but that must never actually appear on the wire.

websocketclose-coderfc6455referencenetwork

How to use WebSocket Close Code Reference / Lookup

  • 1.Enter a close code number, such as one you saw in a browser DevTools WebSocket frame or a server log.
  • 2.Read its name, meaning, and which reserved range it falls in (well-known, library/framework, private use, or reserved for future use).
  • 3.Browse the full list of well-known codes (1000-1015) below the lookup if you're not sure which one applies.

Frequently asked questions

Why do codes 1005 and 1006 say they can't be sent on the wire?
RFC 6455 reserves them for libraries to report internally, 1005 meaning no close code was present at all and 1006 meaning the connection dropped abnormally without a close frame ever being sent. A real close frame is never supposed to carry either value.
What's in the 3000-3999 and 4000-4999 ranges?
3000-3999 is reserved for libraries, frameworks, and applications to register a specific meaning with IANA, so a given code in that range depends entirely on which library defined it. 4000-4999 is reserved for private use and can never be registered, so its meaning is whatever the specific client and server using it agreed on.
Does this cover every possible close code?
It covers the 16 codes RFC 6455 defines directly plus the reserved-range meaning for anything from 1016 up to 4999. Codes above 4999 and below 1000 are not valid close codes and the tool flags them as such rather than guessing at a meaning.
Is any of my data sent anywhere?
No, this is a static reference table. The lookup happens entirely in your browser.

Use via API, SDK, or MCP

cURL# Free: 1,000 req/day · Pro: 10,000 req/day
curl -X POST https://api.utilix.tech/v1/tools/websocket-close-codes \
  -H "Authorization: Bearer utx_live_..." \
  -H "Content-Type: application/json" \
  -d '{"code":1006}'

Get an API key from your dashboard · Full API docs →

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