MessagePack (or "MsgPack") is a serialization format similar to JSON but binary. Unlike JSON but like TOML and YAML it distinguishes between byte arrays and strings and has a timestamp format (as an optional but standardized extension).

There are the following options for working with MessagePack in Tcl.

Library Type Minimum Tcl version MsgPack spec version License Features pure Tcl 8.6 "new" (v5) 3-clause BSD Encoder, decoder, extension formats, timestamp Critcl C extension 8.5 "old" (v4) 3-clause BSD Encoder, decoder pure Tcl ? "new" (v5) MIT Decoder, extension formats pure Tcl 8.5 "old" (v4) MIT Encoder, decoder, extension formats