Compile a PLC from code and read the compile messages

Compiling is the check that tells you whether generated or imported logic is good. With TIA Portal Openness you compile from your program and read the result as objects instead of looking at the Inspector window. This guide does it in C#, then through PLCWare's HTTP API and MCP tools, and ends with how a clean compile leads to a download. It applies to TIA Portal V21.

Before you start

An Openness application connected to TIA Portal V21 with a project open (Set up TIA Portal Openness on Windows).
All devices must be offline while you compile.
If a password protects the safety program, you must log on to the safety program to compile software changes. Otherwise the compile is canceled and an exception is thrown.

Compile with Openness (C#)

Compiling goes through the ICompilable service. What gets compiled depends on the object you ask:

Object	What it compiles
`Device` (the station)	Hardware and software
`DeviceItem` (the CPU)	Hardware only
`PlcSoftware`	The PLC program only
`CodeBlock`, `DataBlock`, `PlcType`	That one object
`HmiTarget`	The HMI software

using System;
using Siemens.Engineering.Compiler;
using Siemens.Engineering.SW;

static bool Compile(PlcSoftware plcSoftware)
{
    ICompilable compiler = plcSoftware.GetService<ICompilable>();
    CompilerResult result = compiler.Compile();

    Console.WriteLine($"State: {result.State}, {result.ErrorCount} errors, {result.WarningCount} warnings");
    Print(result.Messages, "");
    return result.State != CompilerResultState.Error;
}

static void Print(CompilerResultMessageComposition messages, string indent)
{
    foreach (CompilerResultMessage message in messages)
    {
        Console.WriteLine($"{indent}{message.State} {message.Path}: {message.Description}");
        Print(message.Messages, indent + "  ");
    }
}

Every message carries Path, DateTime (always UTC; use ToLocalTime() to show local time), State, Description, WarningCount, ErrorCount and its own child Messages, so the result is a tree, not a flat list.

Compiling only the CPU's DeviceItem checks the hardware and can look clean while the program has real errors. To cover both, compile the Device (or the DeviceItem and the PlcSoftware).

Compile with PLCWare

$r = Invoke-RestMethod -Method Post "http://localhost:5000/plcs/PLC_1/compile" `
  -ContentType "application/json" -Body '{}'
"{0}: {1} errors, {2} warnings" -f $r.state, $r.errors, $r.warnings

PLCWare compiles hardware and software and aggregates the result. An abbreviated answer:

{
  "state": "Error", "errors": 1, "warnings": 0,
  "messages": [
    { "state": "Error", "path": "PLC_1/FB_Motor/Network 3", "dateTime": "2026-09-25T12:00:00Z",
      "description": "...", "children": [] }
  ],
  "sections": [ { "target": "hardware" }, { "target": "software" } ],
  "blockChanges": [ { "name": "FB_Motor_Instance", "detail": "InstanceDB#8", "change": "modified", "parts": ["Interface"] } ]
}

state is the worst state found (Error, then Warning, Information, Success). errors and warnings are totals, and messages is the whole tree, each message with its path and dateTime.
sections details the hardware and the software separately.
blockChanges lists the blocks the compile changed. A modified instance DB means the compile regenerated it after its FB's interface changed: export it and commit it so what you version matches the project.
Only Error blocks a download. Warnings do not.

The MCP tool is tia_compile with { "plc": "PLC_1" }. It flattens the message tree and adds a verification summary (compiled, errors, warnings) and nextHints. tia_block_compile compiles a single block (PLCWare app 1.7.0 or later); a clean block compile is not the check that comes before a download, so compile the whole PLC for that.

Compiling can take a while on a large project. When the answer is status: "running" with a jobId, the compile is still running: call tia_job_status with that jobId until the result arrives, and do not repeat the original call.

When the compile has errors

Read the first errors first: the rest are often consequences. Use each message's path to find the block and the network.
Changing an FB's interface leaves its instance DB inconsistent until a compile regenerates it. Compile again before you start deleting anything.
A CPU created through Openness can fail its first compile with protection errors until its protection settings are set; see Create devices and hardware.
Some errors are settings Openness cannot change, such as the OPC UA runtime license. They are a person's job in the TIA Portal window. In the MCP, tia_guide with { "topic": "gui-gates" } lists them with the exact steps.

From a clean compile to a download

A compile with zero errors is the precondition for downloading to a real PLC, and the download stays a human decision. tia_download works in two steps: first with dryRun: true, which asks the serve app for a verified plan (a clean compile, a PG/PC interface found, a fingerprint of the software) and returns a single-use planHash; then, after a person has read and approved that plan, again with approved: true and the same planHash. If the software changed after the plan, the download is refused with 409 plan_stale. Planning a download needs the Pro scope, which the trial includes; Basic can read, author and compile but cannot plan one.

Start your free 30-day trial

PLCWare runs these steps for you, or for your AI assistant, against TIA Portal V21. The trial lasts 30 days, includes the Pro scopes, needs no card and does not renew. You need TIA Portal V21 with a STEP 7 Professional license, bought separately from Siemens.

Start the free 30-day trial · Download the app

TIA Portal, SIMATIC and Siemens are trademarks of Siemens AG. PLCWare is an independent product for TIA Portal and is not affiliated with or endorsed by Siemens.