The Sensible Soccer ROM editor lets you change the teams, players and kits in the Mega Drive game from your browser. In the technical article I covered how the ROM data is stored and rewritten. This post is a walkthrough of actually using it.
For a first attempt, changing a team’s kit is a useful place to start. It’s easy to spot in the game and doesn’t need any extra space for longer names.
Opening a ROM #
You’ll need your own ROM of the International or Original edition of Sensible Soccer for the Sega Mega Drive. The editor accepts .md and .bin files. It doesn’t support the Amiga or PC versions, and there are no ROM downloads on the site - you’ll have to find a download for it elsewhere.
Keep an untouched copy of your original ROM. Then open the editor and choose Open ROM file, or drag the file into the upload area. Although it looks like an upload control, the ROM is read locally in your browser, not sent to a server.
Once it has opened, the team editor appears further down the page. There are separate categories for national, club and custom teams. Choose a category, then select a team from the list. The search box is useful if you already know which team you want to change.
Changing the kits #
With a team selected, find the kit controls. There are separate settings for the First Kit and Second Kit, each with a preview.
Choose a style, then use the colour controls to change the two shirt colours, shorts and socks. The preview updates as you go, so you can try combinations without downloading the ROM each time.
These changes are kept when you select another team. There’s no separate Save button for each team, but this only saves them within the open page - you still need to download or export your work before leaving.
Team details #
The Team Info section contains the team name, country, coach, formation and skill settings.
The skill scale is worth checking: 0 is best and 7 is worst. The lower the number the stronger the team! The formation menu selects a formation such as 4-4-2 or 4-3-3.
Names are converted to uppercase as you type. The game supports letters A–Z, spaces, hyphens, apostrophes and full stops. Team, coach and player names can be up to 25 characters; the country field is limited to 19. There is also an overall space limit, which I’ll come back to later.
You can leave Flag alone for ordinary team editing. The help text beside it explains that as far as we can tell it isn’t used by the game engine.
Editing the squad #
Each team has sixteen players. You can change their names and shirt numbers, choose their position and appearance, and set the star-player checkbox.
The Position menu handles both the line-up slot and the player’s usual role. Choosing Right midfield, for example, also sets the player as a midfielder. For the bench, choose Substitute — Goalkeeper, Substitute — Defender, Substitute — Midfielder or Substitute — Forward.
Some slots change role with the team’s formation. Where the usual name would be misleading, the menu shows a label such as Defender (slot 7). Changing formation updates players whose stored roles matched the previous formation; substitute types and existing unusual role combinations are preserved.
You can still put two players in the same starting position, but the editor now tells you both which slot is duplicated and which is missing. For example, “Centre midfield has 2 players” and “Missing formation position: Right midfield.” Both conflicting rows are highlighted. Choose the missing position for the player you want to move; the editor doesn’t swap players automatically.
To swap a starter with a substitute, assign the substitute to the starter’s position, then give the outgoing player one of the substitute choices. Each starting slot must be used once, with five substitutes. Shirt numbers must be between 1 and 16.
Some original teams have a stored role which differs from the usual one. These show a Stored role note and are kept as they are when you open a ROM or edit a name. Use usual role explicitly resets that player to the expected role. You can inspect or change the stored roles under Advanced player settings, which is collapsed by default. Choosing another position also sets its usual role again.
For simple name or kit changes, there’s no need to alter the squad positions at all.
Downloading the edited game #
Below the team editor is Download Modified ROM. This creates a new .md file containing your changes. You can then load that downloaded file in your Mega Drive emulator to check the result. For quick testing my favourite is https://www.emulatrix.com/.
If the download button is disabled, look for the validation messages and the error markers on the teams and categories. Errors in another team can prevent a download too.
Also check the Team data line above the button. It shows the bytes used, the total capacity and the remaining space. A name can fit within its individual character limit while still making the complete set of teams too large. In that case, shorten some names until the data fits. Zero bytes remaining is fine, provided there are no other errors.
Saving work for later #
Export JSON saves the team data as a separate file. This is useful for keeping a roster to return to, while Download Modified ROM gives you the file to load in the game. JSON on its own isn’t a playable ROM.
To resume from JSON:
- Open the ROM you were working with, or its original copy from the same edition.
- Choose Import JSON and select your exported file.
- Select a team and carry on editing.
An import replaces the whole team document, not just the selected team. Export your current work first if you want to keep both versions. An invalid import is rejected without replacing your existing edits.
You can also reopen a previously downloaded modified ROM directly. There’s no need to import JSON as well if that ROM already contains the changes you want.
Refreshing or closing the tab loses unsaved edits. Start Over (Open Another ROM) clears the current document too, so download the ROM or export JSON before using it.
Open the editor when you’re ready to try it.