One of the biggest limiting factors to playing modded Paradox Interactive games is that every player must each ensure that they have the correct checksum. Otherwise they just can't play. Oftentimes, people just don't want to play highly modded games because of how much time is eaten up simply trying to get the checksums to match! I would know, many games that I've tried to set up just fall apart because one player is having checksum issues that just seem to never be solved!

However, after fixing checksum issues game after game, I feel pretty confident in being able to fix them quickly. So confident, in fact, that I'm going to put up a guide on how to do it, to make it easier for everyone to play modded games in CK3!

With this guide, I'm going to make it fast and simple to troubleshoot checksum issues and fix them quick!

The guide is ordered in such a way that the easiest fixes are listed first, and the more involved/last resort ones are at the bottom. So, all you have to do is start at the top and work your way down.

However, if you and your friends absolutely want a fix that will work 100% of the time, right from the start, then skip straight to Act 3: The NUCLEAR option. Even though it may take a little more effort than the first two acts, if you start with Act 3, I guarantee that your checksums will match!

That being said, let's get that checksum issue ironed out for you!

If you want to get started right away, skip the next portion and go straight to Act 1. However, I highly suggest you at least take a look at the next part!

Before we get into the fixes proper, I would like to state how much easier having a "collection" makes troubleshooting for everyone.

Collections are a feature of steam that allows you to make, well, a collection. Of mods, that is. This collection can then be sent to other players and they can subscribe to all the mods at once. Easy!

Having collections makes it a whole lot easier to AVOID checksum issues in the first place.

"How's that?!" You ask? Well, I'll tell you.

Let's say you're hosting a game, and seven players connect to the game just fine. Clearly the problem isn't with the host. However, an eighth player is having checksum trouble.

Now, as the host, it is considered to be part of your job to ensure that all the players have the right checksum. So, theoretically, you need to leave the game, kicking all the players from the lobby, just so that you can compare your playset to theirs, to see if there are any missing parts or anything added that shouldn't be there.

HOWEVER, with a collection, you don't need to do any of this. All you have to do is link them the collection, and they can take matters into their own hands, comparing their playset to the collection!

It's a whole lot less pain.


These are just a few tips to put you on the right path:

• You can create a collection by going to the Workshop page, then switching "Browse" from Items to Collections (next to the Home tab). After doing so, you will see a button called "Create Collection" on the right side of the screen.
  
  
• It is important to specify that the collection is made of "Items That Work Together", so you get the Subscribe All button.
  
  
• You should order the mods in the same order they will appear in inside the playset. (I.E. in alphabetical order, if the load order is A to Z, and reverse alphabetical if Z to A.)
  
  
• Prior to beginning a new multiplayer game, go over the collection to make sure that everything is properly in order, and up to date. You don't want any mods in the collection that you don't plan to use in your game! Less confusing for the other players that way.
  -- Be sure to tell players if you updated the collection, so that they can update their playsets in turn!

An example collection that I use in my games:

Oftentimes, the simplest fix is the most effective. A lot of times, you and a player may simply be missing a mod that the other has, vice versa, or a player might simply be using the wrong playset or it's in the wrong order. Basically, playset issues are the most common.

If you are the host of the match, and a very small minority are having checksum issues, then start with the fix below.

HOWEVER, if there are a LOT of people having checksum issues, then start with Act 2.


The fix:

1. Ask a player with the correct checksum to leave the game and open their game launcher
   
   
2. Have the players compare their playsets. Ensure that each player with the wrong checksum sets their load order to A to Z (or to whatever load order everyone else has).
   
   
3. Have the player with the correct checksum read the mods on their playset from top to bottom, making sure that the each other player with the incorrect checksum confirms that it is on their list as well. If not, add it. If one shouldn't be there, take it off.
   
   
4. After this, ask each player to ensure they have selected the correct playset before hitting "Play"
   
   
5. Have the players state their checksum as soon as they load in.

1. Have all players exit the game and go to the game launcher. (Including you!)
   
   
2. Have every single player create a new playset from scratch, and have them all name it something they will remember for the next time they play the save.
   
   
3. List every single mod that you plan to play with, and have everyone (and yourself, of course) add them to the playset one by one.
   
   
4. Be SURE to set the LOAD ORDER to "'A...Z' Load Order" (This is for simplicity. If you need to change the load order, you can have custom, BUT EVERYONE SHOULD HAVE THEIR MODS IN THE PLAYSET BE IN THE SAME ORDER)
   
   
5. Ensure that everyone has the correct playset selected before they start the game.
   
   
6. Have everyone say their checksum when they load in (it's at the bottom right of the main menu screen). It's better to find an issue now than when you're trying to host the match.

Now, assuming that everyone has the correct version of the mods and game installed, this should solve most checksum mismatches.

However, if you're still having problems, that's okay! It can still be solved! We'll just have to dig into a more in-depth fix.

This is the NUCLEAR option, virtually guranteed to work. If you follow this to the letter, and you have any checksum mismatches afterward, I will eat my shoe (I won't actually but you get the point).

Any players that are still having checksum issues at this point must follow these steps:

1. Go into the steam library, click properties on CK3, betas, and make sure that you are all either on "None" or the exact same version
   
   
2. Go to the steam library folder your game is downloaded in (if you don't know, you can right click CK3, go to Manage > Browse Local Files, then press the up arrow until you see the folders "common", "workshop", etc.) and go to the "workshop" folder. Then "content".
   
   Find the folder labeled "1158310" and delete it.
   
   
   
   This will delete all your downloaded mods for CK3 (so you can redownload them in the next step)
   
   
3. Unsubscribe and resubscribe to all mods.
   --- This is where collections can come in handy!
   
   
4. Create a new playset, and have the host go through the mods they going to play with one by one (or simply link the collection and have everyone make a playset from it)
   
   MAKE ABSOLUTELY SURE THAT EVERYONE HAS THE MODS IN THE SAME ORDER.
   (I prefer setting the LOAD ORDER to "'A...Z' Load Order" for its simplicity, but as long as they are all in the same order for every player, it doesn't matter)
   
   
5. Right click CK3, go to properties, local files, then Verify Integrity of Game Files.
   
   
6. Make sure you have selected the correct playset.

If those players complete these steps, and their checksums still don't match, then it's not their fault, they are the ones with the most updated version of the game, and that means everyone else must complete these steps too.

At this point, you've effectively replaced every possible file that could possibly not match with a shiny, new, freshly-downloaded copy. If you're still having issues, your game is cursed.

A commenter to this guide linked a mod that removes the checksum entirely.

Now, I really, really don't suggest starting with this option, because if your checksums are different, but you play anyways, you're likely to have de-sync issues.

So, if you've gone through the previous options and nothing's worked, you could take a look at this mod:

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=3227254722

Thank you for reading! I hope I was able to solve your checksum issue. If I missed anything, let me know in the comments so I can update the guide. Best of luck in your games!