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Web interface for Python's built-in PDB debugger

Project description


GitHub Action tests PyPI version

Web-PDB is a web-interface for Python’s built-in PDB debugger. It allows to debug Python scripts remotely in a web-browser.


  • Responsive design based on Bootstrap.
  • Python syntax highlighting with Prism (“Okaida” theme).
  • Supports all PDB features.
  • Standard input and output can be redirected to the web-console to interact with Python scripts remotely.
  • Current file box tracks current position in a file being executed. Red line numbers indicate breakpoints, if any.
  • Globals and Locals boxes show local and global variables in the current scope. Special variables that start and end with double underscores __ are excluded (you can always view them using PDB commands).
  • Human-readable Unicode literals for Python 2.
  • Command history that stores up to 10 last unique PDB commands (accessed by arrow UP/DOWN keys).
Web-PDB screenshot

Web-PDB console in Chrome browser


Install Web-PDB into your working Python environment:

pip install web-pdb

Insert the following line into your Python program at the point where you want to start debugging:

import web_pdb; web_pdb.set_trace()

The set_trace() call will suspend your program and open a web-UI at the default port 5555 (port value can be changed). Enter in your browser’s address bar: http://<your Python machine hostname or IP>:5555, for example http://monty-python:5555, and you should see the web-UI like the one on the preceding screenshot. Now you can use all PDB commands and features. Additional Current file, Globals and Locals information boxes help you better track your program runtime state.

Note: it is strongly recommended to work with the Web-PDB web-UI only in one browser session. With more than one browser window accessing the web-UI it may display incorrect data in one or more browser sessions.

Subsequent set_trace() calls can be used as hardcoded breakpoints.

Web-PDB is compatible with the new breakpoint() function added in Python 3.7. Set environment variable PYTHONBREAKPOINT="web_pdb.set_trace" to launch Web-PDB with breakpoint().

Additionally, Web-PDB provides catch_post_mortem context manager that can catch unhandled exceptions raised within its scope and automatically start PDB post-mortem debugging session. For example:

import web_pdb

with web_pdb.catch_post_mortem():
    # Some error-prone code
    assert foo == bar, 'Oops!'

For more detailed info about the Web-PDB API read docstrings in the ./web_pdb/ file.

The inspect Command

Web-PDB provides inspect or i command that is not present in the original PDB. This command outputs the list of object’s members along with their values. Syntax: inspect <object_name> or i <object_name>.

Special members with names enclosed in double underscores (__) are ignored.

Considerations for Multithreading and Multiprocessing Programs


Web-PDB maintains one debugger instance that traces only one thread. You should not call set_trace() from different threads to avoid race conditions. Each thread needs to be debugged separately one at a time.


Each process can have its own debugger instance provided you call set_trace with a different port value for each process. This way you can debug each process in a separate browser tab/window. To simplify this you can use set_trace(port=-1) to select a random port between 32768 and 65536.


  • Python: 2.7, 3+
  • Browsers: Firefox, Chrome (all modern browsers should work)


MIT, see LICENSE.txt.

The debugger icon made by Freepik from is licensed by CC 3.0 BY.



  • Updated frontend dependencies.


  • Fixed the issue when a local variable could not be assigned from the debugger console.
  • Updated frontend dependencies.


  • Fixed the issue with closed debugger still being stored in active_instance class property that prevented starting a new debugger session (thanks to maiamcc).


  • Updated frontend dependencies.


  • Fixed using inspect command for variables with None values.


  • Added inspect command.


  • Upgrade Prism.js to v.1.15.0


  • Use gzip compression instead of deflate for web-console endpoints (more info).


  • Bump asyncore-wsgi dependency version. This fixes issues with the web-UI on some platforms.
  • Code cleanup.


  • Use full path for setting and removing breakpoints.


  • Replaced a wsgiref-based multi-threaded WSGI server with a single-threaded asynchronous WSGI/WebSocket server.
  • Implemented WebSockets instead of periodic back-end polling for retrieving updated debugger data.


  • Fix crash when clearing a breakpoint on Linux.
  • Fix autoscrolling on large files.
  • Move frontend to modern JavaScript syntax and tooling.
  • Optimize Python syntax highlighting performance.


  • Fix a bug with patched cl command not working.


  • Fixed setting set_trace() at the last line of a Python script.
  • Fixed clearing a breakpoint at setups with the current workdir different from the current module directory.


  • Internal changes.


  • Now if web-console data haven’t changed the back-end sends “null” response body instead of a 403 error.


  • Implemented a multi-threaded WSGI server to increase responsiveness of the web-UI.


  • Added deflate compression for data sent to a browser.
  • Attempt to fix Current file box auto-scrolling.


  • Logger fix.


  • Minor UI redesign.
  • Added a quick action toolbar and hotkeys for common commands.
  • Added a quick help dialog.
  • Breakpoints can be added/deleted with a click on a line number.
  • The Currrent file box is not auto-scrolled if the current line hasn’t changed.
  • Multiple set_trace() and post_mortem() calls are processed correctly.
  • Added random web-UI port selection with port=-1.


  • Initial PyPI release

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