JMRI Web Access

Basic Use

JMRI supports working with your layout from a web browser.


Details of the JMRI web components.

JMRI JSON Protocol

The JMRI JSON Protocol provides access for a number of JMRI-defined entities, and is accessible through multiple methods:


The JMRI JSON Servlet provides web access to lists and values for numerous JMRI-defined entities, in the modern JSON format. It also provides a WebSocket interface for making changes to the state of those entities, and listening for external changes.

Setting up the JSON Servlet

The JMRI JSON Servlet is a feature that is part of the Web Server. In order to use this service, you'll need to do the following:


The HTTP feature of the servlet responds to the following URL patterns:

There are a number of lists, and not all operations are supported on these lists and/or items within each list. Check the sections below for the operations that are currently supported.

List Names

Currently the servlet supports the following list names used for GET operations to return lists or messages. Singleton types return a message, list types return an array containing all items of requested type.

Name GET PUT POST Returns:
blocks * block array
cars * car array
configProfiles*configProfile array
consists * consist array
engines * engine array
hello * hello message and power message
layoutBlocks * layoutBlock array
lights * light array
locations * location array
memories * memory array
metadata * metadata array
networkServices * networkService array
node * node message
panels * panel array
power * * * power message
railroad * railroad message
reporters * reporter array
roster * rosterEntry array
rosterGroups * rosterGroup array
routes * route array
signalHeads * signalHead array
signalMasts * signalMast array
sensors * sensor array
systemConnections * systemConnection array
time * time message
trains * train array
turnouts * turnout array

Note that these names are case sensitive, so you must supply them as shown above. As an example, let's say you issued the following GET command:


The would return JSON that looks something like this:


The returned data consists of two parts:

Type Names

Here are the different type names supported for the second pattern, along with which HTTP operations are supported:

block * * * PanelPro
car * OperationsPro
consist * * * * DecoderPro
engine * OperationsPro
layoutBlock * * PanelPro
light * * * PanelPro
location * OperationsPro
memory * * * PanelPro
metadata * DecoderPro
reporter * * * PanelPro
roster * DecoderPro
rosterEntry * DecoderPro
rosterGroup * DecoderPro
route * * PanelPro
sensor * * * PanelPro
signalHead * * PanelPro
signalMast * * PanelPro
train * * OperationsPro
turnout * * * PanelPro


You can also insert, update, or delete items in the lists above using the HTTP POST, PUT, and DELETE methods. Not all combinations are supported.

You can use these type names to set values. Continuing with the power example above, you can turn the power on by posting to a URL like this:


With this as the body



The WebSocket feature of this servlet currently handles JSON strings in four different forms:

The WebSocket feature of the servlet can be seen by browsing to the /json/ url, where a JSON console is providing for testing.
Example commands and responses:

command response notes
{"type":"sensor","data":{"name":"IS2"}} {"type":"sensor","data":{"name":"IS2","state":4}} request current state of sensor IS2
{"type":"sensor","data":{"name":"IS2","state":4}} {"type":"sensor","data":{"name":"IS2","state":4}} set sensor IS2 to InActive (4)
{"type":"turnout","data":{"name":"IT99","state":0}} {"type":"turnout","data":{"name":"IT99","state":4}} sending state=0 is also treated as request for current state
{"type":"power","data":{}} {"type":"power","data":{"state":2}} power does not need a name
{"type":"memory","data":{"name":"IMCURRENTTIME"}} {"type":"memory","data":{"name":"IMCURRENTTIME","userName":null,"comment":null,"value":"2:53 PM"}} get (fast)clock time, resent each minute
{"type":"ping"} {"type":"pong"} ping request and response
{"list":"panels"} [{"type":"panel","data":{"name":"ControlPanel/R&R","URL":"/panel/ControlPanel/R&R?format=xml","userName":"R&R","type":"Control Panel"}},{"type":"panel","data":{"name":"Layout/Waccamaw%20Coast%20Line","URL":"/panel/Layout/Waccamaw%20Coast%20Line?format=xml","userName":"Waccamaw Coast Line","type":"Layout"}}] request a list of panels, respond with array, example shows two panels
{"type":"throttle","data":{"throttle":"CSX754","address":754}} {"type":"throttle","data":{"address":754,"speed":0.0,"forward":true, "F0":false,"F1":false,"F2":false,"F3":false,"F4":false,"F5":false,"F6":false,"F7":false, "F8":false,"F9":false,"F10":false,"F11":false,"F12":false,"F13":false,"F14":false, "F15":false,"F16":false,"F17":false,"F18":false,"F19":false,"F20":false,"F21":false, "F22":false,"F23":false,"F24":false,"F25":false,"F26":false,"F27":false,"F28":false, "throttle":"CSX754"}} request throttle for address 754, refer to it as "CSX754"
{"type":"throttle","data":{"throttle":"CSX754","speed":0.25}} {"type":"throttle","data":{"speed":0.25,"throttle":"CSX754"}} request speed of throttle "CSX754" to 25%
{"type":"throttle","data":{"throttle":"CSX754","release":null}} {"type":"throttle","data":{"release":null,"throttle":"CSX754"}} release the throttle "CSX754"
{"list":"trains"} If list is empty:[] Example showing list response if there are no objects of that type.
{"type":"block","data":{"name":"IB1"}} {"type":"block","data":{"name":"IB1","userName":"AUTOBLK:1","comment":null,"value":"ns2608"}} request current value for block IB1


The JMRI JSON server is functionally identical to the JSON WebSocket, but running over a standard network socket.


jquery.jmri is a JavaScript library that ships with JMRI and makes the JSON protocol support just work on most current browsers.
Note: The support for non-WebSocket browsers is limited by the number of open connections allowed. Maybe 5-10 active objects.

Examples of use of the jquery.jmri JavaScript library that ships with JMRI include (example links assume you are reading this on your JMRI web server):