I recently got an script tool in a tbx file to play with.

I'd like to see how the tool runs in a debugger to get a better idea of how it works. I've tried several paths to this, but all of them seem to have failed:

  1. Open in visual studio, or some other IDE: the windows explorer, of course, does not recognize .tbx as a container, and just displays garbage.
  2. Right click the tool and use the "Debug" option: tool runs as usual, but I have no control over stepping, breakpoints, etc. I can't see the code as it is running.
  3. Right click the tool and use the "Edit" button: python script opens in NotePad. There doesn't seem to be a way to choose another editor. Of course, notepad doesn't have a build or compile option, so I can't modify the code even to print output.
  4. Copying the code into Visual Studio and running it there: when trying to run debug from ArcMap, I run into this issue
  • Right click on the python tool and hit edit. See here to better understand script tools in an ArcToolbox.
    – Barbarossa
    Commented Aug 4, 2015 at 16:02
  • Python never has to be compiled.
    – nmpeterson
    Commented Aug 5, 2015 at 0:07
  • It never has to be compiled, but it can be. I tried making obvious edits in notepad which should have thrown bugs, but the script did not change. Hence, I assumed the tool used a compiled version to run.
    – user41428
    Commented Aug 5, 2015 at 15:02

2 Answers 2


To debug Python toolboxes I usually have a separate "debug.py" file in my project where I test just certain modules or code snippets. The script is very simple, set up like this:

import os
import arcpy

def main():
    # code to test here, set break point and step thru

if __name__ == "__main__":

When a Python toolbox throws an error, I inspect the line number and copy the function or method that contains the line in question into debug.py. I hard code the various input parameter values that the tool would normally have, and step thru my code and find exactly what the error is. Finally, I apply the changes to the Python toolbox .pyt file. I am currently using Visual Studio code to run my Python scripts.


I want to add this link as well: How to Debug Python Toolboxes in 3 Easy Steps. This article shows another easy method of debugging a python toolbox simply by adding a main() method:

class MyToolbox(object):
    def __init__(self):

class MyTool(object):
    def __init__(self):
        self.label = 'Tool 1'

def getParameterInfo(self):
    # parameters..
    return params

def execute(self, parameters, messages):
    # do stuff..

def main():
    # set break point here, step thru
    tbx = MyToolbox()
    tool = MyTool()
    tool.execute(tool.getParameterInfo(), None)

if __name__ == "__main__":

Here is how I typically debug/edit python files for python script tools in ArcMap (and how ESRI suggests doing it)

First, set your editor (such as PythonWin or Wing) in Geoprocessing > Geoprocessing Options. Next, in the Catalog window, right-click your tool and click Edit.

Geoprocessing doesn't read your script code until you click OK on the script tool dialog box or press ENTER while in the Python window.

A common workflow when working with Python script tools is as follows:

  • Edit your script (using PythonWin or IDLE, for example) and save your changes, but don't exit the editing application.
  • Run the script tool.
  • If need be, make more code changes, saving your edits but not exiting the editing application.
  • Run the script tool again.
  • When you're satisfied that your script is working correctly, exit the editing application.
  • Sweet! Geoprocessing>Geoprocessing Options was just what I needed!
    – user41428
    Commented Aug 4, 2015 at 16:40

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