Unknown error (PY)” when trying to upload a new release of my mod.

[behroozzx]

Hello,

I am experiencing the same “Unknown error (PY)” when trying to upload a new release of my mod.

Mod: The Cave
Mod Portal page: https://mods.factorio.com/mod/the-cave
Current published version: 3.1.31
Version I am trying to upload: 3.1.44
Account username: behroozzx

I have fully tested version 3.1.44 locally in Factorio. The mod installs and loads correctly, I can create and load a game with it, and I have actually played the game with this version enabled. Everything works correctly in the game and I have not encountered any mod-loading or gameplay errors.

I also checked the ZIP structure and rebuilt the archive, but the Mod Portal still rejects every upload attempt with the same “Unknown error (PY)” message.

The previous version, 3.1.31, was uploaded successfully. Version 3.1.44 is approximately 92 MB and is well below the upload size limit.

The ZIP file is available here:
https://drive.google.com/file/d/1WQd-xJ ... sp=sharing

Could a Factorio staff member please check the uploader/server logs to determine what is causing this error?

Thank you.

[Tachigami Itsuki BY]

Hi, you from "CIS" country?

[Tachigami Itsuki BY]

I have the same problem, I'm from Belarus

[behroozzx]

Hi I'm from UNITED KINGDOM (UK)

[behroozzx]

Could we please receive an official response regarding this issue?

The same problem was first reported three days ago, but so far no moderator or Factorio staff member has acknowledged it. There are now at least two mod authors from different countries—Belarus and the United Kingdom—experiencing exactly the same “Unknown error (PY)” when uploading a new release. I have also contacted support by email but have not received a response.

This is preventing us from publishing fully tested mod updates. The ZIP installs and runs correctly in Factorio, its structure is valid, and it is within the permitted upload size.

Could someone from the Factorio team please confirm whether this issue is being investigated and check the Mod Portal upload logs? Even a brief acknowledgement or status update would be appreciated. If this forum is not the correct place to report it, please tell us which official channel we should use.

We understand that the team may be busy, but receiving no response at all while the Mod Portal continues to block releases is extremely frustrating.

Thank you.

[Sanqui]

Hello, I will investigate this error as soon as I can (this evening)!

[behroozzx]

Thank you very much for your response and for taking the time to investigate this. I truly appreciate it.

I’m very relieved to know that the issue is now being looked into, and I’ll be eagerly awaiting your update. If you need any additional details, upload timestamps, or another copy of the ZIP file, please let me know and I’ll provide them immediately.

Thank you again for your help!

[behroozzx]

Good news — I have just managed to upload version 3.1.44 successfully.

Immediately after my previous reply, I removed the existing very long changelog and replaced it with only a few lines for the latest version. I then repacked and uploaded the mod, and the Mod Portal accepted it straight away. No other relevant part of the mod was changed.

This strongly suggests that the “Unknown error (PY)” was triggered by the changelog file—possibly because of its total length, a parser limit, or a formatting issue in one of the older entries.

I wanted to share this before your investigation in case it helps you locate the exact backend error. It would still be very helpful to know the precise cause, since the portal displayed only an unknown error without any actionable validation message.

Thank you again for looking into this!

[Tachigami Itsuki BY]

Similarly, as I understand it, there is a limit on the size of the change list.

[behroozzx]

Yes, that may very well be the cause. Shortening my changelog allowed the upload to succeed immediately.

However, I think we should wait for the Factorio staff investigation to confirm whether this is simply a changelog size limit or a bug in the changelog parser. Hopefully, they can also clarify the exact limit and replace the “Unknown error (PY)” with a more useful error message.

[behroozzx]

While waiting for the staff investigation, I carried out some additional tests and research to determine whether the Mod Portal has a documented changelog-size limit.

According to the official Factorio documentation:

* The changelog-format documentation states that each version may contain an arbitrary number of categories and entries. It also says that the Mod Portal does not require the strict in-game changelog format and displays `changelog.txt` as plain text. I could not find any published character-count or file-size limit:
https://lua-api.factorio.com/latest/aux ... ormat.html

* The official Mod Upload API documentation lists the possible upload errors, including the generic `Unknown` error, but does not specify any maximum size for `changelog.txt`:
https://wiki.factorio.com/Mod_upload_API

* The Mod Portal API describes the changelog simply as an optional string and does not publish a maximum length:
https://wiki.factorio.com/Mod_portal_API

I also checked the changelog pages of several large, successfully published mods and measured the currently displayed changelog text:

* Pyanodons Alternative Energy: approximately 63,626 characters
https://mods.factorio.com/mod/pyalterna ... /changelog

* Krastorio 2: approximately 103,000 characters
https://mods.factorio.com/mod/Krastorio2/changelog

* Space Exploration: approximately 309,284 characters
https://mods.factorio.com/mod/space-exp ... /changelog

These are approximate counts of the visible changelog text, measured from the first `Version:` entry to the page footer. They are not raw file sizes in bytes, so encoding and line-ending differences may affect the actual file size. Nevertheless, they demonstrate that the Mod Portal currently accepts changelogs significantly larger than 64,000 or 100,000 characters.

For The Cave 3.1.44, I performed the following controlled test:

1. The package containing my complete historical changelog repeatedly failed with `Unknown error (PY)`.
2. I removed the old changelog history and kept only three or four lines for the latest release.
3. I repackaged the same release without changing any other relevant part of the mod.
4. The Mod Portal accepted the upload immediately.

This strongly indicates that `changelog.txt` was the trigger. However, it does not yet prove that the total character count alone was the cause. It could instead be:

* An undocumented high size limit.
* A limit on the number of lines or version sections.
* A particular character, encoding, or line-ending issue.
* A malformed entry somewhere in the older history.
* A backend, parser, or database edge case.

Since Space Exploration currently displays approximately 309,284 changelog characters successfully, any simple character-count limit would presumably need to be higher than that, or the actual restriction may be based on something else, such as raw byte size, encoding, or the internal structure of the changelog.

Could the Factorio team please check the logs from the failed uploads and confirm:

1. The exact backend error that caused the upload to fail.
2. Whether an official hard limit for `changelog.txt` exists, including its exact value and unit.
3. Whether that limit can be added to the official documentation.
4. Whether the Mod Portal can return an actionable error message—such as `Changelog exceeds the permitted size` or the location of an invalid entry—instead of `Unknown error (PY)`.

Shortening the changelog allowed me to publish version 3.1.44, so the immediate problem is resolved. However, identifying the exact cause would help other mod authors avoid the same issue and would make future upload failures much easier to diagnose.

Thank you again for investigating this.