Summary: The Java Model Railroad Interface is a suite of programs. JMRI offers DecoderPro for decoders and PanelPro for layout automation, as well as other features.
As the name says, JMRI is built upon Java technology, giving it a degree of platform independence. Your computer must be capable of running Java. The version of Java that will work with your computer determines the features JMRI offers you.
- A database of decoders and a graphical interface for programming their features
- A database/inventory component
- An automation component for your layout
JMRI interfaces to many different command stations. Don't worry about trying to just install JMRI – the components are bundled together. 
You do not need to learn/use all parts of the suite, for example to program a decoder, it is not necessary to run the inventory or the layout automation components.
The Java Model Railroad Interface
Version Numbering Scheme
JMRI uses a simple version number system.
The most current version of JMRI is on their webpage, currently Version 5.X.Y.
- Production releases are identified by an even number for the X value. This is the version you want to download for normal use.
- For a Development release, the value of X is odd. These are available for testing and development purposes only, which you can install if you wish, although most users will not benefit from a development release. After testing and fixing issues, the final development version is released to the community as a production version.
- The value of Y indicates an incremental update.
There is much more information available on the JMRI web site.
How can I Help with JMRI?
If you find JMRI to be useful, donations are appreciated to help cover the costs of providing JMRI to the community, and help defray the costs of defending JMRI during the Jacobsen v. Katzer lawsuit. The result was an important decision regarding Open Source Software. Even the NMRA became involved to protect their DCC Standards from questionable patents. In the end the decision benefited the Model Railroading community immensely.
Contributing Software to JMRI
You can get more info on working on improving JMRI.
JMRI supports a number of DCC systems and hardware:
- Atlas Commander
- Lionel TMCC
- Oak Tree Systems
- Protrak Grapevine
- Uhlenbrock Intellibox
- Viessmann Commander
- Zimo MX-1
For a current list of supported hardware see the JMRI Website.
- Mac OS X
- Mac OS
- MS Windows
A compatible version of JAVA is required. The current JMRI 5 requires Java 11.
- JMRI 4.X will run on Windows XP or Windows Vista SP1, provided Java 1.8 is installed. Installation is a little difficult as Oracle's Java website will warn you that XP is obsolete, but an install package is still available. To install Java on Windows XP, download an Offline version for installation. Oracle does not support Java on XP, and it may break at any time. See JMRI Install Guide Windows for more information.
- The JMRI site also mentions that computer hardware running current versions of MS Windows is available on the used market cheaply. It may be easier to buy a used computer which is compatible with recent versions of Java for a reasonable price than trying to upgrade an old one. See the install page for recommended hardware specs.
JMRI 5 and Java 11
The current release of JMRI (Version 5.x) will not work with Java 8. An upgrade to Java 11 is required, older (4.x.x) releases work with Java 11.
Uninstall Java 8 prior to installing Java 11, otherwise the Java 11 installation will not be recognized.
Oracle no longer offers the JRE (Java Runtime Environment) needed, but their JDK (Java Development Kit) supports current and upcoming JMRI releases. See the links below for more information on obtaining a suitable version of Java 11 for your platform.
MacOS Big Sur
Apple has made internal changes to the MacOS Big Sur which have rendered many USB to Serial bridges useless by deprecating their drivers. If you are contemplating upgrading to a newer version of the Mac OS, verify that the interface you are using is supported. Many third-party drivers have not been updated. Some may never be.
The fall 2020 release of MacOS Big Sur presented challenges to running JMRI. For safety, the Mac OS will not accept many older device drivers, requiring updated drivers. Unfortunately, many vendors haven't bothered to do that. Therefore, you may have to purchase new hardware to connect your Mac to your layout. It is advisable to wait before updating to the newest OS versions due to these reasons.
FTDI is working on new drivers, which are not available yet.
- Apple included drivers for FTDI's chipsets with their OS over the past several updates. Unfortunately, they only support certain FTDI devices. The LocoBufferUSB and ESU's USB to Serial devices require an updated driver. Otherwise, most FTDI based devices should still work. 
Apple Silicon Support
JMRI can be used natively or through emulation on newer Macs featuring the Apple Silicon integrated circuits. See the MacOS Notes above.
JMRI Users can find technical support on via a very active JMRI User Group available on GroupsIO. The mailing list is populated by users and developers, so a solution to your issue can be found.
The JMRI Components
What can I do with JMRI?
- Use DecoderPro to configure your locomotive decoders and keep a roster of your DCC equipped locomotive fleet.
- PanelPro can run locomotives, throw turnouts, control signals, and even create control panels. But you shouldn't expect it to be as powerful as a commercial layout management program; JMRI isn't meant to compete directly with them.
- Use the LocoTools application with your Digitrax command station to control your layout, monitor communications, configure add-on devices, etc.
- The JRMI interfaces allow you to write programs for your own layout. Making this easy is an important goal. This can be done via the scripting language, or by adding new Java code to the program.
- Write new general-purpose tools. Although this is a little harder than writing automation for your own layout, writing tools that other people use can be very satisfying.
- Implement the JMRI interfaces for a new system. Having JMRI work with other systems is an important goal. Once an implementation for another system works, the general tools (e.g., symbolic programmer, automations tools, signalling, etc.) can be immediately used.
JMRI - DecoderPro
Many people that have expensive track control software still use this software for its ability to quickly program a wide range of decoders. The JMRI suite of programs runs on Mac Classic and OS X, Linux, and Windows machines, all under Java. All major manufacturers of DCC equipment, systems and decoders, are supported.
JMRI - Layout Automation
Layout Automation applications provide a large number of ways of automating your layout, ranging from simple fill-in forms to full-fledged scripting and programming capabilities. These include:
- A simple form of automation is to define Routes, which allow you to simplify the control of your turnouts.
- Signal logic
- JMRI provides built-in signalling logic which can be used to drive your signal heads in many applications.
- JMRI provides a very powerful scripting tool. Based on a real programming language, it gives you access to all the JMRI capabilities.
- Writing your own code in Java
- The JMRI libraries greatly simplify writing a program to make your layout do exactly what you want.
JMRI - PanelPro
PanelPro is an application for operating CRT based CTC control panels that reflects the real-time state of your railroad and let you control it - almost like a Prototype dispatcher.
JMRI - LocoNet™ Tools
LocoNet Tools contain a number of LocoNet tools. Please see link for further details.
- LocoNet monitor
- Display and log the traffic on the LocoNet, in either hex or human readable form.
- Slot monitor
- Packet source
- A tool to let you type and send packets to the LocoNet
- BDL16, BDL162 and PM4 programmers
- A tool to let help you configure BDL16, BDL162 and PM4 boards.
- LocoIO programmer
- A tool to let help you configure a LocoIO board.
There is a known bug in JMRI 4.16 that can disable operation of a LocoBuffer-USB.
If you have a LocoBuffer-USB and this issue appears, the solution is to upgrade to version 4.17 or higher of the JMRI software.
JMRI Installation & Intro to DecoderPro
JMRI and RFID
JMRI® & DecoderPro® are registered trademarks of the JMRI Community. PanelPro™, SignalPro™, TrainPro™, DispatcherPro™, OperationsPro™ are trademarks of the JMRI Community.
- There have been many arguments over the years about this, but for technical reasons bundling everything into one package is a more efficient use of resources as components can be shared and thus effectively maintained.
- FDTI Drivers may brick counterfeit devices.