Textures and models

F1 25's art, models, worlds and menus live in .erp archives under 2025_asset_groups/. Inside each archive are named resources, each with one or more fragments. To change them, add ERP operations to your data addon and list the file in operations.erp:

"operations": {
  "erp": ["erp/texture.json"]
}

With the in-game loader, the build delivers changed and added resources as overlay archives under swofty/assets/resources/, and the stock archives stay in the game folder. Without it, the build writes a new copy of each archive your operations touch. See Build route and runtime route.

Look inside an archive

Start by finding the resource you want to change. Use tools/erp.py to list what's in an archive:

python3 tools/erp.py "2025_asset_groups/f1_safetycar_package/safety_car_2/wep/safety_car_2.erp" '*'

Each line gives you the resource type and name, followed by one tuple per fragment. Read each tuple as fourcc, decompressed size, packed size, flags, compression:

GfxSurfaceRes eaid://f1_safetycar_package/safety_car_2/textures/safety_car_2_decal_da.tif.image [('temp', 349528, 174763, '0x10', 17), ('temp', 73, 73, '0x10', 145)]

Here, compression 17 means zstd (0x11), and 145 means stored (0x91). For your operation's resource field, copy the whole resource name, including the eaid:// prefix. To inspect the bytes, extract the resource's first fragment with tools/erpx.py; it decompresses the fragment for you:

python3 tools/erpx.py "2025_asset_groups/f1_safetycar_package/safety_car_2/wep/safety_car_2.erp" safety_car_2_decal_da out.bin

For the file format, see ERP archives.

Replace a fragment

Use replace-resource when you want to swap one fragment for a raw file from your addon and keep the others. Choose the fragment to match what you're changing: a texture's fragment 0 is its header, while fragment 1 holds its top-mip pixels:

{
  "schema_version": 1,
  "ops": [
    {
      "op": "replace-resource",
      "erp": "2025_asset_groups/ui_package/screens/fe_loading.erp",
      "resource": "eaid://ui_package/art/textures/loading/background.tif",
      "fragment": 0,
      "source": "erp/background.tif"
    }
  ]
}

Your source file must hold raw fragment bytes: the data you'd get after decompression. The build compresses those bytes the way the archive stores that fragment, then updates the sizes and resource hash. If you leave out fragment, it defaults to 0. Give erp paths relative to the game folder and source paths relative to your addon folder.

Copy a resource between archives

If you already have the resource in another archive, use copy-resource to append it to erp, byte for byte. Choose source for an archive in your addon, or from_erp for one the game ships. Use as to give the copy a new name:

{
  "op": "copy-resource",
  "source": "erp/car.erp",
  "erp": "2025_asset_groups/f1_2026_vehicle_package/teams/toro_rosso/wep/toro_rosso_barcelona_26.erp",
  "resource": "eaid://f1_2026_vehicle_package/teams/toro_rosso/wep/toro_rosso.wep",
  "as": "eaid://f1_2026_vehicle_package/teams/toro_rosso/wep/toro_rosso_barcelona_26.wep"
}

Choose a name that isn't already in erp, or the copy fails. Adding a livery shows how to copy a whole car this way.

Add a resource

To append a new resource built from raw files, use add-resource with one file per fragment. Set type to the resource type (at most 15 characters), then list the fragment files in order under sources. The new resource gets its fragment names, flags and compression from the first resource in erp that matches both its type and fragment count:

{
  "op": "add-resource",
  "erp": "2025_asset_groups/ui_package/screens/fe_loading.erp",
  "resource": "eaid://ui_package/art/textures/loading/sponsor.tif.image",
  "type": "GfxSurfaceRes",
  "sources": ["erp/sponsor.head.bin", "erp/sponsor.pixels.bin"]
}

Use put-resource to replace a resource of the same name or add it if it's missing. To take one out, use remove-resource. The loader can't remove a resource from a stock archive, so a build with any remove-resource rewrites the archives into the game folder and prints erp: built into the game files; <n> resource removal(s) cannot apply at runtime.

Merge texture array slices

Team logos and flags sit in texture arrays: one resource whose slices are separate images. When several addons change different slices of one array, use merge-slices instead of put-resource. Ship the whole array in an archive in your addon, and the build writes only the slices that differ from the game's:

{
  "op": "merge-slices",
  "erp": "2025_asset_groups/vfx_package/common.erp",
  "resource": "eaid://ui_package/art/texture_arrays/overrides.uidb/overrides.team_logos.f1_2026.texarray.image",
  "source": "logos/ui_textures.erp"
}

Each addon's changed slices go over the array the addons before it wrote. Two addons that change different logos both show. See Texture arrays for arrays of another size or format.

Add mip files

A texture's remaining mip chain lives outside the archive, in a loose .mipmaps file. Fragment 2 holds its path. To supply that file, use add-mipmaps to copy one file, or a folder of them, to a path in the game folder:

{ "op": "add-mipmaps", "source": "mipmaps/", "target": "f1_safetycar_package/safety_car_2/textures/" }

If you supply a folder, every file under it is copied, keeping the paths below target. Then point your texture at the new mip file by replacing fragment 2 with replace-resource.

Patch a !pkg resource

Worlds, layers and UI databases are !pkg resources: trees of named entries. With patch-pkg, you can edit entries in that tree while keeping the rest of the archive unchanged. Here's how Custom Grid Size adds a pit garage to a track's grid layer:

{
  "op": "patch-pkg",
  "when": { "cars": 26 },
  "erp": "2025_asset_groups/environment_package/tracks/monaco/wep/monaco_f1_26_myteam.erp",
  "resource": "eaid://environment_package/tracks/monaco/wep/monaco-vehicles_current_myteam.layer",
  "edits": [
    {
      "op": "clone-entry",
      "at": "instances",
      "src": "[name=vehicles_current_myteam$PitGarage23]",
      "as": "vehicles_current_myteam$PitGarage25",
      "set": {
        "uniqueid": "a5256e66c3b302404d61d63301e06514",
        "overrides.VehPlacement.Id": 25,
        "overrides.WorldObject.transform": [-0.33035, 0.0, -0.94385, 0.0, 0.0, 1.0, 0.0, 0.0, 0.94385, 0.0, -0.33035, 0.0, -334.457, -14.192, 255.083, 1.0]
      }
    }
  ]
}

Edit	Fields	Effect
clone-entry	at, src, as, optional set, from	Copy src in the container at, name the copy as, and apply set. In an array, src is a [field=value] selector and as is the new selected field. from takes the entry from another resource (erp, resource, fragment)
set-value	path, value	Set one value

To find the entry you need, extract the fragment, then read its tree with python3 tools/pkg.py text <fragment.bin>. Address entries with dots and [field=value] selectors. Your replacement value takes the existing value's type, so supply a number for an int or float, 16 numbers for a mat4, or a hex string for a woid.

Not built yet

Only clone-entry and set-value are built; the other patch-pkg edits are defined but not built. If you use one of those other edits, the build skips all your addon's ERP operations and warns you.

Settings and warnings

You can use when and {{id}} with db settings in ERP files, just as you would in database operations. To print a message at build, use warn:

{ "op": "warn", "when": { "cars": 30 },
  "message": "Monaco has room for 28 cars; a 30-car race there leaves 2 cars without a grid slot." }

Build and check

swofty build

On the runtime route, the output counts your resources in runtime: swofty/assets.json with ... <n> resource(s). On the build route, it lists each rewritten archive as replace 2025_asset_groups/.... It also prints every warn message, each archive it had to rewrite, and each conflict.

Reference

• ERP operations: every operation and field.
• Operations: how ERP files fit with the other operation kinds, order and conflicts.
• ERP archives and !pkg resources: the file formats.
• Editing menus: ship an edited menu scene with replace-resource.