Player-session MUD protocol
GMCP
Generic MUD Communication Protocol
Widely used
Documented current use
A bidirectional package and JSON channel for vitals, rooms, characters, chat, UI, media, and other structured game data.
Protocol overview
- First seen
- 2010
- Present-day status
- Widely used
- In use today?
- Yes, with documented current use.
- Legacy?
- No.
- Layer
- Player-session MUD protocol
- Transport
- Telnet option 201 with UTF-8 JSON
- Telnet option
- 201
- Research validated
Current use and fit
The principal modern structured-data protocol across major MUD clients and several current engines.
Implementation essentials
- Offer WILL GMCP, wait for DO, then exchange package-name and JSON subnegotiations.
- Track package names and versions through Core.Supports.
- Apply payload, nesting, and update-rate limits.
Compatibility and safety notes
- GMCP defines framing, not one universal package schema.
- Reject malformed JSON at the protocol boundary.
- Use an RFC 1143-style Telnet option state machine to prevent loops.
Original specifications and sources
- MUDhalla technical specification Primary
- MUD Standards preservation Preservation
Where an original site has disappeared, a preservation archive is linked and identified as such. MUDVerse does not claim authorship of the original protocol.