· ReadyStack
Worked example
Real numbers from this tool, line by line.
Six PySimpleGUI ties turned up in one 9-line requirements.txt, the file a Python developer keeps for an internal Windows desktop tool at a small company in the US or Europe. Three are errors, two are warnings and one is an info line:
| Line | PySimpleGUI line | Replacement line |
|---|---|---|
| 2 | --extra-index-url https://PySimpleGUI.net/install | delete; PySimpleGUI>=6,<7 is LGPL3 on PyPI |
| 3 | PySimpleGUI==5.0.8.3 | FreeSimpleGUI==5.3.0.post1 or nicegui==3.18.0 |
| 4 | PySimpleGUI==4.60.5 | FreeSimpleGUI==5.3.0.post1 |
| 5 | PySimpleGUIQt | FreeSimpleGUIQt==2.0.0 |
| 6 | PySimpleGUIWeb==0.39.0 | FreeSimpleGUIWeb==1.1.0 |
| 7 | PySimpleGUIWx==0.17.2 | FreeSimpleGUIWx==1.1.0 |
The errors are the ones that break a fresh install. On 2026-10-10 the PySimpleGUI.net/install index returned HTTP 404, so pip falls back to PyPI. On PyPI, PySimpleGUI 5.0.8.3 is a stub: its PySimpleGUI.py only prints "PySimpleGUI is now located on a private PyPI server". There is no Window class in it, so the tool dies on its first sg.Window call. A bare PySimpleGUIQt installs version 5.0.0, and its PyPI licence field reads "Free To Use But Restricted".
What PySimpleSoft changed, and when
PySimpleGUI 5 launched as a paid product in February 2024. Hobbyists registered a free key, and companies were expected to buy a commercial licence at $99 per developer. The notice on the 5.0.8.3 PyPI page says only 600 people paid that $99. PySimpleSoft announced the shutdown in February 2025 and kept support for commercial users through the end of 2025. Hobbyist keys run until they expire, and no new ones are issued.
On 2026-04-14 PySimpleGUI 6 was published on PyPI under LGPL3, with the licensing and security components removed. The latest is 6.3.0.1 from 2026-08-16. So the old answer, "PySimpleGUI needs a paid licence", is now only true for the 5.x line. Many answers written before April 2026 still give it.
Three ways out
- FreeSimpleGUI 5.3.0.post1 is the LGPL fork of the last free release. Its README shows the whole change as one line: import FreeSimpleGUI as sg. The Qt, Wx and Web ports have FreeSimpleGUIQt 2.0.0, FreeSimpleGUIWx 1.1.0 and FreeSimpleGUIWeb 1.1.0.
- PySimpleGUI 6 under LGPL3: pin PySimpleGUI>=6,<7 and delete the private index line. It is one maintainer's code, and the README says pull requests are not accepted.
- NiceGUI 3.18.0 (MIT) or Flet 1.0.4 (Apache-2.0): a rewrite. sg.Text becomes ui.label, sg.Button becomes ui.button, and the window.read() loop becomes callbacks. It is a bigger job, but it gives you a maintained toolkit and a browser UI.
How the check reads a file
The extension has 9 rules. It reads requirements*.txt, pyproject.toml (PEP 621 and Poetry), setup.py, setup.cfg, Pipfile and imports in .py files. A version ceiling decides the rule: ==5.0.8.3 is the stub, >=5,<6 is proprietary 5.x, <5 is the LGPL3 4.x line, and >=6 is clean. An as-of date input changes severity, too. Before 2026-01-01 the 5.x lines are warnings, because support still ran. After that date they are errors.
The migrated file has FreeSimpleGUI==5.3.0.post1, FreeSimpleGUIQt==2.0.0, nicegui==3.18.0 and flet==1.0.4, and it gives zero findings.
Free and with a key
The open file is free, with every tie and every replacement line. A one-time key adds the whole-workspace migration plan, a dated licence-exposure report for the company, and a CI gate that fails a build adding new PySimpleGUI 5 use.
15 seconds — what it actually does
Questions people ask
What does NiceGUI Migration Check do?
It reads requirements.txt, pyproject.toml, setup.py, setup.cfg, Pipfile and Python imports and lists every PySimpleGUI tie: the PySimpleGUI.net/install private index, the PySimpleGUI==5.0.8.3 PyPI stub, proprietary 5.x pins, a bare PySimpleGUIQt that installs the restricted 5.0.0, the old Wx and Web ports and each import. Every finding carries its line number and the FreeSimpleGUI, PySimpleGUI 6 or NiceGUI replacement line. It has 9 rules.
Who is NiceGUI Migration Check for?
It is for Python developers and small internal-tools teams who built desktop utilities on PySimpleGUI between 2018 and 2025 and now have to decide where to go: FreeSimpleGUI as a drop-in, PySimpleGUI 6 under LGPL3, or a rewrite in NiceGUI or Flet. It also suits the person at a company who must answer which projects ever pulled proprietary PySimpleGUI 5.
Why not just grep for PySimpleGUI or ask a chatbot?
A text search finds the name but not the meaning of each line. A bare PySimpleGUIQt installs version 5.0.0, whose PyPI licence field says Free To Use But Restricted. PySimpleGUI==5.0.8.3 is a stub that only prints a move notice. PySimpleGUI 6 has been LGPL3 since 2026-04-14, which many answers written earlier still miss.
What is free and what needs a licence key?
Free and without a key: the open file is checked on save or on command, and every PySimpleGUI tie is listed with its line and the replacement line. Nothing in that answer is hidden. A one-time licence key adds the whole-workspace migration plan with sg elements mapped to NiceGUI or Flet, a dated licence-exposure report and a CI gate for new PySimpleGUI 5 use.
What did staying on PySimpleGUI 5 cost?
PySimpleSoft sold the PySimpleGUI 5 commercial licence at 99 US dollars per developer, according to the notice on the PySimpleGUI 5.0.8.3 PyPI page, which also says only 600 people paid it. PySimpleSoft has shut down and support ended with 2025. FreeSimpleGUI and PySimpleGUI 6 are LGPL3, NiceGUI is MIT and Flet is Apache-2.0.
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