TTYPE AND MTTS  [protocol]
How a client tells a server what it is and what it can do — including, if the
client chooses to say so, that a screen reader is in use.
https://www.mudhalla.net/tintin/protocols/mtts/

Measured adoption
  0 of 886 listed games were observed offering it (0.0%)
  /games?protocol=TTYPE

  The games not counted here are not games without the protocol. A game is
  counted when we observed its server offering the option in a handshake; the
  rest are servers that did not offer it to us and servers whose handshake we
  have not read, and we cannot tell you which.

  By codebase, of the games we identified
    AresMUSH             0 of 18 offered it
    CircleMUD            0 of 47 offered it
    CobraMUSH            0 of 2 offered it
    CoffeeMUD            0 of 32 offered it
    DikuMUD              0 of 35 offered it
    Evennia              0 of 11 offered it
    FluffOS              0 of 28 offered it
    MUCK                 0 of 24 offered it
    PennMUSH             0 of 34 offered it
    RhostMUSH            0 of 40 offered it
    ROM                  0 of 55 offered it
    SMAUG                0 of 20 offered it
    tbaMUD               0 of 5 offered it
    TinyMUSH             0 of 9 offered it

TTYPE is telnet option 24, from RFC 1091: the server asks the client what
terminal it is, and the client answers. Historically the answer was VT100 or
ANSI.

MTTS — the Mud Terminal Type Standard — layers a convention on top. A client
answers three times: its name, its terminal type, and then MTTS <bitmask>, where
the bits declare capabilities. 256 colours, true colour, UTF-8, MNES, MSP over
out-of-band — and, notably, MTTS_SCREEN_READER.

THE SCREEN-READER BIT

That last one is worth pausing on, because it is the only place in this hobby's
protocol stack where accessibility is a first-class concept.

A client that sets it is telling the server that a screen reader is in use, and
a server that notices can adapt: suppress ASCII art, drop the decorative
box-drawing around a room description, change how a table is laid out. Both
TinTin++ [/reference/clients/tintin] and Blightmud
[/reference/clients/blightmud] advertise it, and Mudlet
[/reference/clients/mudlet] has a setting for it.

Whether any given game acts on it is a different question, and not one this site
can measure — we cannot ask a server what it would do differently.

WHAT A CRAWLER OWES HERE

A crawler identifies itself through TTYPE, and it should. Ours does, with an
information URL, so an administrator reading their logs can find out who has
been connecting to their game and how to ask us to stop. A crawler that answers
ANSI and nothing else is anonymous by design, and there is no good reason for
that.

WHAT WE MEASURE

Servers that negotiated TTYPE with us. Note that this is one of the few options
where we are the side being asked, so a figure here is a count of servers that
cared to ask.

See also
  CHARSET — /reference/protocols/charset
  TinTin++ — /reference/clients/tintin
  Blightmud — /reference/clients/blightmud