Your game was working yesterday. Today it crashes on launch, shows a "missing executable" error, or an update downloaded and now nothing starts. Before you reach for the nuclear option — uninstalling and re-downloading 80 GB — try verifying the integrity of the game files. Every major PC launcher has this built in, it takes a few minutes, and it fixes a surprising share of broken installs.
What "verify integrity" actually does
When a launcher installs or updates a game, it keeps a manifest: a list of every file the game should contain, with a checksum for each one. Verification walks through your local installation, re-computes the checksum of each file, and compares it against the manifest. Any file that is missing, truncated or corrupted gets re-downloaded from the launcher's servers. Everything else is left alone.
Three things this means in practice:
- It only downloads what is broken. If 3 files out of 40,000 are corrupt, you download 3 files — not the whole game.
- It does not touch your saves or settings in most cases. Those live in separate folders (Documents, AppData) that are not part of the verification manifest.
- It reverts modded files to stock. If you installed mods by overwriting game files, verification will "repair" them back to the originals. Back up your mods first.
When verifying is the right fix
- The game crashes during or immediately after launch, especially after an update or a power cut.
- You see errors about a missing executable, missing
.dll, or "content file locked". - A download was interrupted — the launcher says the game is installed, but it will not start.
- Mods or a manual tweak broke something and you want a clean slate without a full reinstall.
- An antivirus quarantined a game file and the game now fails its own checks.
It is also worth doing before you update graphics drivers or reinstall Windows for a game problem. Verification is five minutes; a driver reinstall is an afternoon.
Steam: verify integrity of game files
- Open Steam and go to your Library.
- Right-click the game and choose Properties.
- Open the Installed Files tab. (In older Steam clients this tab is called Local Files.)
- Click Verify integrity of game files.
- Wait for the progress bar to finish. Steam reports how many files failed validation and re-acquires them automatically.
For large games this can take 10–20 minutes on a hard drive, much less on an SSD. You can keep using Steam for other things meanwhile, but do not launch the game being verified. If Steam reports "1 file failed to validate and will be reacquired" every single time you check, that is usually a file the game itself rewrites on launch (a shader cache or config) — harmless, and not something you need to chase.
Epic Games Launcher: verify files
- Open the Epic Games Launcher and click Library in the left panel.
- Find the game, then click the three dots (
…) on its tile. - Choose Manage from the menu.
- Click Verify next to "Verify files".
- The game tile will show the verification running as a download-style progress bar. Let it finish, then launch the game.
Epic's verifier is the most quietly placed of the three — the Manage screen also holds the launch options and installation folder, so it is worth knowing where it is. Like Steam, it only re-downloads the damaged parts of the installation.
GOG Galaxy: verify / repair
- Open GOG Galaxy and select the game in your library.
- Click the settings/customization icon — the small sliders icon next to the Play button.
- Hover over Manage installation.
- Click Verify / Repair, then confirm.
- GOG Galaxy checks the installation against its servers and re-downloads anything mismatched. Progress shows under Downloads in the left panel.
One GOG-specific note: Verify / Repair only works for GOG games. If you added a Steam or Epic game to Galaxy as a shortcut via an integration, Galaxy cannot verify it — use the game's own launcher instead.
Quick reference: where the button lives
| Launcher | Path to verification |
|---|---|
| Steam | Library > right-click game > Properties > Installed Files > Verify integrity of game files |
| Epic Games Launcher | Library > … on the game tile > Manage > Verify |
| GOG Galaxy | Select game > sliders icon next to Play > Manage installation > Verify / Repair |
What verification will not fix
Verification only repairs the files on your disk. It cannot fix:
- Corrupted save files. Saves are not part of the manifest. If a save is corrupt, you need a backup or an earlier save slot.
- Driver and OS problems. A game that crashes because of a broken GPU driver will crash identically after verification.
- Server-side issues. If the game's servers are down, no amount of local file checking helps.
- Bugs in the game itself. Verification restores the game to the state the developer shipped — including the developer's bugs.
If verification finds nothing wrong
A clean verification result is still useful information: it tells you the installation is fine, so the problem is elsewhere. Work through these next:
- Update (or roll back) your graphics drivers — a driver update that landed the same day the game broke is the prime suspect.
- Disable overlays one by one: Steam, Discord, GeForce Experience and Xbox Game Bar overlays all inject into games and can cause launch crashes.
- Run the game as administrator once, to rule out a permissions problem writing to its folders.
- Check the game's community forum or our fix lag and stutter guide — if the problem started for everyone after a patch, the fix is usually a settings change, not a reinstall.
- Only then consider a full uninstall and reinstall, and back up your saves first.
Verification is the closest thing PC gaming has to a "have you tried turning it off and on again" for broken installs: quick, safe, and effective often enough that it should always be step one.
