wsjtx-mcp
An MCP server that controls WSJT-X
(FT8/FT4/JT65/MSK144/Q65/WSPR…) from MCP clients such as Claude Desktop and the
MCP Inspector.
It is the weak-signal leg of an "operate → log" trio for amateur radio:
- fldigi-mcp — operate broad
digital modes via fldigi (XML-RPC).
- n3fjp-mcp — log QSOs to
N3FJP (TCP API).
- wsjtx-mcp (this one) — operate the FT8/FT4 weak-signal world via WSJT-X
(UDP message protocol).
⚠️ Experimental (v0.1). Transmit is gated behind your callsign and you keep
the operator in command. Read the Transmit safety section.
How it is different
WSJT-X does not offer a request/response API. It broadcasts state over UDP
(Status, Decode, QSOLogged, Heartbeat, …) and honours a small set of
inbound control messages. So this server runs a background UDP listener that
continuously parses datagrams and keeps the latest status, a buffer of decodes,
and completed QSOs — you read those, and nudge WSJT-X with control messages.
Consequences worth knowing up front:
- No dial-frequency control over UDP. You can read the dial frequency from
Status, and set mode/sub-mode/Rx DF/T-R period via configure, but QSY is a
rig-control concern (Hamlib/CAT or the UI), not this server.
- You can start and halt Tx, but cannot toggle "Enable Tx". Transmission is
started by answering a CQ (
reply) or by free_text with send=true, and
stopped by transmit halt. There is no UDP command for the "Enable Tx",
"Auto Seq", "Call 1st", or "Hold Tx Freq" checkboxes — those stay UI settings.
reply gives hands-free QSOs only when WSJT-X's "Auto Seq" is on. A reply
is equivalent to double-clicking a CQ; with Auto Seq enabled (the usual
FT8/FT4 default) WSJT-X then sequences the whole exchange to QSOLogged with no
further calls. With Auto Seq off, reply starts only the first transmission.- Best for search-and-pounce, weak for RUN. The API is built to answer CQs
(and only CQ/QRZ decodes), so S&P is fully automatable. It has no clean way to
drive a repeating call-CQ (RUN) cycle — that needs WSJT-X's own "Enable Tx",
or a
free_text CQ re-sent each period.
Requirements
- WSJT-X 2.1 through 3.x — the UDP message protocol is schema 3 / Qt_5_4 and
has been stable across those releases (verified live against WSJT-X 3.0.2).
- In WSJT-X: Settings → Reporting → UDP Server
- UDP Server = the host running this server (default
127.0.0.1), port
2237.
- Accept UDP requests = ON to allow control (it is OFF by default).
Observing decodes/status works without it; commanding does not.
Install (Claude Desktop)
Download the wsjtx-mcp.mcpb from the
latest release and
double-click it, or drag it onto Claude Desktop → Settings → Extensions. Fill in
the settings form (callsign, host, port). See docs/INSTALL.md.
Configuration
| Variable | Default | Purpose |
|---|
WSJTX_HOST | 127.0.0.1 | UDP address to bind/listen on. |
WSJTX_PORT | 2237 | WSJT-X UDP Server port. |
WSJTX_CALLSIGN | (empty) | Operator callsign — the single transmit gate. Blank = receive-only. |
WSJTX_MULTICAST | (off) | Optional multicast group to join (coexist with other UDP consumers). |
WSJTX_INSTANCE | (auto) | Target a specific WSJT-X Id when several instances broadcast. |
Host/port are where this server listens; control replies are sent back to the
address each datagram arrived from.
| Tool | Kind | What it does |
|---|
status | observe | Latest Status snapshot + listener/instance health. |
diagnostics | observe | Host/network + bind status + datagram counts + gate state. |
decodes | observe/nudge | read / drain (poll new) / clear_local / replay. The RX plane. |
log | observe | Buffered completed QSOs (QSOLogged + LoggedADIF) → feed N3FJP. |
reply | transmit | Answer a buffered CQ/QRZ decode (auto-sequences the QSO when WSJT-X "Auto Seq" is on). |
free_text | transmit if send | Set the Tx5 free-text message; send=true keys the radio. |
transmit | control | halt / halt_auto — stop transmitting (UDP can't enable Tx). |
configure | control | Mode/sub-mode/Rx DF/T-R period/freq-tol/DX call+grid. No dial freq. |
clear | control | Clear the Band Activity / Rx Frequency windows. |
highlight | control | Colour or clear a callsign in Band Activity. |
location | control | Override the session Maidenhead grid. |
switch_config | control | Switch to a named WSJT-X configuration. |
annotate | control | Set a Fox/Hound sort-order annotation for a DX call (niche, DXpedition). |
wsjtx_call | escape hatch | Build & send any message type by name (gate still applies). |
Transmit safety
The callsign is the single transmit gate, exactly as in fldigi-mcp. With
WSJTX_CALLSIGN blank the server is receive-only: it refuses every
transmit-initiating message — reply, free_text with send=true, and any
keying message via wsjtx_call. transmit halt, clear, configure,
highlight, location, replay, and all reads are always available (they don't
put you on the air; halt takes you off).
Beyond that gate:
- Per-transmit approval comes from the Claude Desktop tool-permission prompt —
lean on it for human-in-the-loop control.
- WSJT-X's own Tx Watchdog and the
Tx Enabled / Transmitting flags
(surfaced in status) are extra safety signals.
- Operating under Part 97 automatic/remote control is the operator's
responsibility: ensure station identification and a control operator who can
intervene.
Only one process can normally own UDP 2237 on a host. If JTAlert, GridTracker,
or N1MM already consume it, either point WSJT-X's secondary UDP server here, use
a multicast group (WSJTX_MULTICAST) so several listeners coexist, or run
this server on a different host. To reach a WSJT-X on another machine, install
the mcp-host-bridge tool
(mcp-host-bridge install wsjtx --to <rig-host>) and set WSJTX_PORT=2238 —
sandboxed MCP clients reach only loopback, and the bridge does the LAN hop. See
docs/REMOTE-HOST.md.
Development
uv sync
uv run ruff check .
uv run pytest
The protocol codec is pure standard library and unit-tested against byte
fixtures, so the tests need no running WSJT-X. A smoke_test.py proves a live
WSJT-X is reachable receive-only. The field-tested message reference lives in
docs/WSJTX-API.md.
License
MIT © 2026 Stefan Brunner (AE5VG)