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One free scan finds every outdated or missing driver and matches the right update for your exact hardware.Free scan · exact hardware matchIn Steam, an ACF file is usually a plain-text application manifest—not the game itself. The most important form is appmanifest_<AppID>.acf, stored in a library’s steamapps folder. It records how Steam views an installed app, including its name, installation directory, state, size, build and depot information.
The manifest helps Steam recognize files that are already on a drive, but it is not a backup, ownership proof, save-game archive or replacement for the game directory. Steam can still validate files, download updates or fetch missing content.
What an ACF file means in Steam
“ACF” is not a single universal format with one settled acronym expansion. In Steam discussions, it generally means a text-based application configuration or manifest file. The filename and location are more useful than the expansion of the acronym.
Steam’s app manifests use Valve’s KeyValues-style structure: quoted keys and values, nested sections in braces, and numbers commonly stored as strings. Technical references describe the observed format rather than a permanently guaranteed public schema (ACF format reference).
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"AppState"
{
"appid" "730"
"name" "Example Game"
"StateFlags" "4"
"installdir" "Example Game"
}A real file contains more fields, and Steam may add, remove or reinterpret them over time.
ACF file versus the actual game
Steam library
└── steamapps
├── appmanifest_123456.acf ← Steam’s local installation record
└── common
└── Game Folder ← Executables and game dataThe manifest sits directly in steamapps; the game normally sits in steamappscommon (or the equivalent Linux path). An ACF does not contain the game’s executable files, a compressed backup, your Steam password, ownership entitlement or all of your saves. It also cannot prove that every file on disk matches the current Steam build. Steam describes appmanifests as the records that identify installed games and support manual backups (Steam Community guidance).
Where Steam stores ACF files
The structural path is:
<Steam library>/steamapps/appmanifest_<AppID>.acfTypical Windows examples are C:Program Files (x86)Steamsteamapps and D:SteamLibrarysteamapps. Linux and SteamOS use Linux-style paths under a home directory or mounted drive. The invariant is the steamapps relationship, not a particular drive letter.
Steam can have several libraries, each with its own steamapps directory. Find the active library in Steam’s storage settings rather than searching only the main installation folder. Library-location files and parsers are documented by valve.go’s Steam folder package.
How to identify the right manifest
Use the AppID
In appmanifest_123456.acf, the number is the Steam AppID. It commonly matches the number in a store address such as store.steampowered.com/app/123456/. Verify it in the file rather than trusting the filename alone.
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Check the internal values
Open a copy in a plain-text editor and compare appid, name and installdir with the Steam library entry and the folder under common. Do not confuse the AppID with depot IDs or Workshop item IDs; one game can reference several depots.
What an appmanifest commonly contains
appid: the application’s Steam identifier.name: display name.installdir: directory name understeamapps/common.StateFlags: installation and state information.SizeOnDisk: Steam’s recorded installed size.buildidand update timestamps.InstalledDepotsandMountedDepots: depot and manifest data.- Download state, user configuration, shared-depot and install-script information where applicable.
These are commonly observed fields, not a stable public contract. Do not assume an unfamiliar key is disposable.
Is it safe to open, copy or edit?
Opening and backing up
Reading an ACF with Notepad or another plain-text editor is normally safe. Exit Steam before copying or changing files, and preserve both the manifest and game directory:
<library>steamappscommon<Game folder>
<library>steamappsappmanifest_<AppID>.acfUse a plain-text editor, not a word processor that adds formatting. A manifest can reveal installed games, paths and timestamps, so review it before posting publicly.
Editing
Manual edits are best limited to diagnosis. Changing depot records, manifest IDs, build identifiers, state flags, paths or download counters can make Steam show the app as uninstalled, repeatedly validate it, redownload content or fail to update. “Steam can parse this file” does not mean that it accurately describes the files on disk.
Copy a known-good manifest or let Steam regenerate one before attempting hand edits. Never download a replacement manifest from an unknown site or use an “ACF fixer” that asks for credentials.
Move an installed game without starting from zero
- Exit Steam completely.
- Add or create the destination library using Steam’s storage controls.
- Copy the game folder into the destination library’s
steamapps/commondirectory. - Copy the matching
appmanifest_<AppID>.acfinto that library’ssteamappsdirectory. - Restart Steam and let it inspect the installation.
- Resume or verify the installation if Steam schedules one, allowing it to discover existing files.
This may avoid a full redownload, but it cannot repair missing files, supply a changed build or bypass ownership checks. Steam’s documented discovery workflow notes that additional downloads can still be required (Steam-hosted instructions).
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If the file is missing
- Back up the existing game folder.
- Start installing the same game to the intended library so Steam creates its own manifest.
- Pause the installation.
- Place the existing files in the folder Steam selected.
- Resume and let Steam discover and validate them.
Do not fetch a random ACF online. Steam can create a current manifest tied to your account and library.
If the file is corrupt
- Close Steam and copy the damaged file somewhere safe.
- Restore a known-good backup if you have one.
- If not, rename or remove only that game’s manifest while Steam is closed.
- Start an installation in the correct library and let Steam regenerate the record.
- Allow validation and any necessary downloads.
Deleting an ACF is a controlled troubleshooting action, not a universal repair. Do not begin by deleting libraryfolders.vdf or unrelated manifests.
Why Steam shows “Install” when files exist
| Likely cause | What to check |
|---|---|
| Manifest was not copied | Look for the matching appmanifest_*.acf in the same library’s steamapps folder. |
| Wrong library | Confirm the drive and library are registered in Steam. |
| Folder-name mismatch | Compare installdir with the directory under common. |
| Wrong AppID | Compare the filename and internal appid with the store entry. |
| Incomplete or different build | Let Steam validate; missing or changed depots may download. |
| Drive unavailable or path changed | Reconnect and re-add the library through Steam’s storage controls. |
| Malformed manifest | Restore a backup or let Steam regenerate it. |
A folder under common alone is not enough; Steam needs the library registration and matching installation record.
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App manifests and Workshop manifests are different
| File | Typical role |
|---|---|
appmanifest_<AppID>.acf |
Local installation metadata for a Steam app or game. |
appworkshop_<AppID>.acf |
Workshop subscription and download metadata for an app. |
libraryfolders.vdf |
Steam library-location information. |
appinfo.vdf |
Broader application metadata and cache. |
A game may have both an appmanifest and a Workshop manifest; neither substitutes for the other. Workshop ACF naming is documented in Steam community discussions (example).
Inspect manifests with PowerShell
These read-only commands list manifests and display the beginning of one. Replace the path with the actual library:
Get-ChildItem "D:SteamLibrarysteamappsappmanifest_*.acf" |
Select-Object Name, Length, LastWriteTime
Get-Content "D:SteamLibrarysteamappsappmanifest_730.acf" -TotalCount 40Third-party parsers can help inventory libraries, but they must tolerate undocumented format changes; they are not an official Steam API (parser discussion).
What an ACF cannot recover
- Game files that were never copied or are damaged.
- Required depots or a newer build.
- Steam ownership or authentication.
- Save data stored locally, in Steam Cloud, under userdata or by another launcher.
- Separate launcher, redistributable or anti-cheat components.
The Bottom Line
Keep the matching appmanifest_<AppID>.acf with the game folder when moving or backing up a Steam installation. Read it freely, edit only with a backup and a specific reason, and let Steam regenerate it when it is missing or damaged.
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