Mirth Connect is the workhorse of healthcare integration — an open-source integration engine (now owned by NextGen Healthcare and officially called NextGen Connect) that thousands of organizations use to move and transform messages between clinical systems. At the center of Mirth is one concept: the channel. A channel receives messages, processes and transforms them, and sends them where they need to go, and once you understand how channels are built, you understand how to integrate with Mirth. This tutorial is a practical orientation to channel development — the anatomy of a channel, each component, and how to build, deploy, and monitor your first one.
A scope note: this is a technical tutorial, not legal advice, and messages flowing through Mirth channels carry PHI, which must be protected with appropriate security and a BAA where applicable.
What Mirth Connect Is
Mirth Connect is a cross-platform, Java-based integration engine purpose-built for healthcare. Its job is to connect systems that speak different protocols and formats — receiving HL7 v2 over MLLP from one system, transforming it, and delivering it as something another system understands, for example. It is the most widely used open-source engine in the space, which means deep community knowledge and broad familiarity. (We cover how it compares to alternatives in our Mirth vs Redox comparison, and the open-source-versus-commercial naming nuance in our related NextGen Connect article linked below.) The unit you actually build in Mirth is the channel, so that is where this tutorial focuses.
The Anatomy of a Channel
A channel is a message pipeline with three conceptual parts. A source connector receives inbound messages. One or more destination connectors send messages out. And in between, filters decide whether a message should be processed, while transformers modify it. A message flows in through the source, optionally passes a source filter and transformer, gets encoded, and then is handed to each destination, where it can again be filtered, transformed, and sent. Understanding this flow — source, then per-destination processing — is the mental model for everything else, because every channel, however complex, is built from these same pieces.
Source Connectors: How Messages Come In
The source connector defines how a channel receives messages, and Mirth offers several types. The classic is the TCP/MLLP listener (LLP Listener), which receives HL7 v2 messages over MLLP — the standard way HL7 v2 flows between systems. Others include an HTTP listener (for web requests and REST-style input), a File Reader (picking up files from a directory), a Database Reader (polling a database), a Web Service listener, and a JavaScript Reader for custom logic. The source type you choose depends on how the sending system delivers messages; for HL7 v2 feeds like ADT, MLLP is the usual answer — see our HL7 integration practice and our HL7 ADT messages explainer.
Data Types and HL7 Parsing
Mirth works with multiple data types — HL7 v2.x, XML, JSON, delimited, raw, and others — and a key strength is that it parses HL7 v2 into a navigable structure you can address by segment and field. When a channel’s inbound data type is HL7 v2, Mirth converts the pipe-delimited message into an internal representation (XML-like) so you can read and manipulate PID, PV1, OBX, and other segments cleanly in your transformers, rather than parsing delimiters by hand. Choosing the right inbound and outbound data types for a channel is a foundational configuration step, because it determines how you work with the message throughout.
Filters: Accept or Drop
A filter determines whether a message continues processing. At the source or a destination, you can add filter rules — often a simple condition on message content — that accept or drop the message. For example, a destination might filter to only process ADT A01 and A03 events, dropping the rest. Filters keep channels focused and prevent systems from receiving messages they do not need, and they are a clean way to route by content without complicating the transformation logic.
Transformers: Modifying the Message
Transformers are where the real work of reshaping data happens. A transformer is a sequence of steps applied to the message, and Mirth provides built-in step types — the Mapper (extract a value into a variable), the Message Builder (set a value in the outbound message), and others — alongside the option to write a JavaScript step for anything custom. Transformers move and reformat data: pulling a field from an inbound HL7 segment, mapping a code, building the outbound message structure. Data passes between steps and destinations through Mirth’s variable maps — the connector map, channel map, response map, and global maps — which let you stash a value in one place and use it in another. Learning the maps is essential, because they are how information flows across a channel’s stages.
JavaScript in Mirth
Mirth is heavily JavaScript-driven (it runs a JavaScript engine under the hood), and most non-trivial channels involve JavaScript in filters and transformers. You work with the inbound message through msg and build output through tmp, navigating HL7 structures by segment and field, and you have the full power of JavaScript for logic the built-in steps cannot express. For reuse, Mirth provides code templates — shared JavaScript functions you can call across channels — which keep common logic in one place rather than copied into every channel. Good Mirth development leans on code templates and clear, well-organized JavaScript rather than sprawling inline scripts.
Destination Connectors: Sending Messages Out
Destinations define where processed messages go, mirroring the source connector types: a TCP/MLLP Sender (to send HL7 v2 onward), an HTTP Sender (to call a web service or REST API), a File Writer, a Database Writer, a JavaScript Writer, and more. A channel can have multiple destinations, each with its own filter and transformer, so one inbound message can be transformed differently and sent to several systems. Destinations can also be chained and can use the response from one in another. This is how a single ADT feed, for instance, can be fanned out — transformed and delivered to a lab system, a billing system, and a FHIR endpoint, each in the form it expects. For sending to FHIR, see our FHIR API development practice and our HL7 v2 to FHIR migration guide.
Deploying and Monitoring Channels
Channels are built and managed in the Mirth Administrator, the GUI where you configure connectors, filters, and transformers, then deploy the channel to make it live. Once deployed, the Dashboard shows channel status and statistics (messages received, filtered, sent, errored), the message browser lets you inspect individual messages and their transformations at each step, and logs surface what is happening. This visibility is one of Mirth’s strengths: when something goes wrong, you can open the message browser, see exactly what arrived and how it was transformed, and diagnose the issue rather than guessing. Monitoring is part of operating channels, not an afterthought.
Error Handling and Reliability
Reliable channels handle failure explicitly. Mirth tracks message status (received, transformed, sent, error, filtered), logs errors, and lets you reprocess messages that failed — invaluable when a downstream system was briefly unavailable. You can configure alerts to notify you of errors, and for HL7 v2 over MLLP you handle acknowledgments (ACKs) so senders know whether their messages were accepted. Designing for error handling — knowing what happens when a destination is down, when a message is malformed, or when a transformation throws — is what separates a channel that works in testing from one that holds up in production where things inevitably go wrong.
Building Your First Channel
Create the Channel and Set Data Types
Create a new channel and set its inbound and outbound data types (for an HL7 feed, HL7 v2.x inbound).
Configure the Source Connector
Choose and configure the source — for an HL7 v2 feed, a TCP/MLLP listener on the right port.
Add a Filter If Needed
Add a source or destination filter to accept only the messages or events you care about.
Build the Transformer
Use Mapper and Message Builder steps (and JavaScript where needed) to extract, map, and build the outbound message, using the variable maps to pass data along.
Configure the Destination
Choose and configure the destination connector — MLLP sender, HTTP sender, file or database writer — to deliver the transformed message.
Deploy
Deploy the channel from the Administrator to make it live.
Test and Monitor
Send test messages, watch the Dashboard and message browser to confirm correct processing, and verify acknowledgments and error handling.
Best Practices
A few habits make Mirth development sustainable: use code templates for shared logic instead of copying JavaScript across channels; name channels, connectors, and steps clearly so the interface is understandable months later; handle errors explicitly rather than assuming the happy path; test with realistic messages, including malformed ones, before going live; avoid over-stuffing one channel with too many unrelated responsibilities; and manage channel versions so changes are tracked and reversible. These are the difference between a Mirth environment that stays maintainable and one that becomes a tangle nobody wants to touch.
How Taction Helps
We design, build, and maintain Mirth Connect (NextGen Connect) channels and integration environments — configuring source and destination connectors, building filters and transformers, writing clean JavaScript and reusable code templates, handling acknowledgments and errors, and setting up monitoring so interfaces are reliable and observable. We integrate HL7 v2, FHIR, and other formats, and bridge between them where needed. With deep integration-engine experience, ISO 27001-certified security, and PHI handled under a signed BAA, we keep your interfaces dependable. Our Mirth Connect integration practice, within our healthcare software work, covers the full scope.
Related reading: HL7 ADT Messages Explained · NextGen Connect vs Mirth Connect: What’s the Difference?
Frequently Asked Questions
What is a channel in Mirth Connect?
A channel is a message pipeline: it receives messages through a source connector, optionally filters and transforms them, and sends them out through one or more destination connectors. Channels are the core unit of work in Mirth — every integration you build is one or more channels.
What’s the difference between a filter and a transformer?
A filter decides whether a message should be processed (accept or drop it), while a transformer modifies the message — extracting, mapping, and building data. Filters control flow; transformers reshape content. Both can run at the source and at each destination.
Do I need to know JavaScript to use Mirth?
For simple channels, the built-in steps (Mapper, Message Builder) and filters can take you a long way without code. For anything non-trivial, yes — Mirth is heavily JavaScript-driven, and transformers and filters often use JavaScript. Code templates let you share common JavaScript logic across channels.
How do I send one message to multiple systems?
Use multiple destination connectors on a channel. Each destination has its own filter and transformer, so one inbound message can be transformed differently and delivered to several systems — for example fanning an ADT feed out to a lab system, billing, and a FHIR endpoint, each in the format it expects.
How do I monitor and troubleshoot channels?
The Mirth Administrator’s Dashboard shows channel status and statistics, and the message browser lets you inspect individual messages and their transformation at each step. Combined with logs and configurable alerts, this lets you see exactly what arrived and how it was processed, which makes troubleshooting concrete rather than guesswork.
What happens when a message fails?
Mirth tracks message status and logs errors, and you can reprocess failed messages — useful when a downstream system was briefly down. You can configure alerts for errors, and for HL7 v2 over MLLP you handle acknowledgments so senders know the outcome. Designing explicit error handling is essential for production reliability.
Building or maintaining Mirth Connect integrations? Schedule a free consultation →
This article is a technical tutorial, not legal advice. Reviewed by Taction Software’s healthcare integration engineering team. ISO 27001-certified information security management. Messages in Mirth channels carry PHI, protected under a signed BAA.
