Sanity

A Lethal Company mod that gives each player a hidden sanity meter.

Being alone, deep inside the facility, out at night, or scared drains it. The ship, your teammates (meeting up after time alone), fresh air after a long trip inside and bringing loot home bring it back. When it gets low, you start experiencing symptoms that only you can see or hear. They're built from the game's own sounds and effects, so you can't easily tell them apart from the real thing, and your crewmates can't confirm them either. No new monsters, no custom assets, and nothing that can really hurt you.

⚠️ Disclaimer: use at your own risk

• Made with AI. The code was written by an AI coding assistant (Claude Opus 5.5, by Anthropic), and the design was worked out with its help. The direction and decisions come from a human side with limited programming knowledge.
• No code review yet. The code hasn't been read through by an experienced programmer, so there may be bugs, rough edges, or things done in an odd way.
• Limited playtesting. It has been played over a handful of sessions, by one small group, with one modpack. Other setups may turn up problems.
• It's early. Balance will change between versions.
• It's built to fail quietly (if something it needs is missing, that effect is skipped instead of breaking the game), but no guarantees: the license says it's provided "as is", without warranty of any kind.

That said, it's safe to play. It adds no items or monsters, never touches your real health or your save file, and everything it does stays on your own screen, apart from two small effects (see Multiplayer). It has been played through full sessions without breaking anything. The points above are about being honest, not a warning that something is wrong.

Experienced modders: if you feel like looking through the code, any help or advice is very welcome (see Feedback). Otherwise, have fun, and please report what you find.

Symptoms (spoilers)

• Flicker: the lights flicker when one is right there (in view, or you're standing in it); at lower sanity your flashlight stutters or cuts out.
• Phantom fear / dread: the game's fear music, screen filter and heartbeat, with nothing there.
• Phantom sound: a monster that could be on this moon makes a sound behind you. Nothing's there.
• Phantom steps: footsteps passing, following you at your pace, or rushing up behind you.
• Phantom walkie: your walkie clicks on as if a teammate pressed theirs.
• Phantom hit: you get hit by nothing; the health it took comes back slowly, on your screen only.
• Locked door: the door you reach is locked. Use a key on it and the key is gone.
• Vanishing item: the loot you're walking up to isn't there when you reach it.
• Lost time: you step out of the facility after a long trip inside and it's night.
• The Presence: something unseen moves around you for a while: its steps, its voice, the lights.

How sanity is calculated, and the design behind each symptom, is in docs/design.md.

Multiplayer: who needs it?

Only you. Each player who has the mod gets their own meter and their own symptoms. Players without it, and the host, don't need it, and mismatched versions are fine: the mod sends no messages of its own.

Almost everything happens only on your screen. Two small things can reach other players, both through the game's own code:

• The locked door's key. If you use a key on the fake locked door, the key really is used up, through the game's normal key use. To everyone else it looks like you used a key.
• The phantom hit's flinch. While your character flinches from a phantom hit, the game's updates of your body's animation to other players pause for about a second, so they don't see a flinch. At most, your character looks briefly stuck in the animation it was in.

Also worth knowing: a vanished item is only hidden for you. Your teammates can still see it and pick it up.

Install

Install it with a mod manager (Thunderstore Mod Manager, r2modman, Gale): it brings BepInEx with it.

Manual install: put Lowlight.Sanity.dll in BepInEx/plugins (BepInEx 5 required).

Config

Editable in-game with LethalConfig (optional), or in BepInEx/config/Lowlight.Sanity.cfg.

Compatibility

• Health displays: works with LethalHUD and GeneralImprovements (they show the phantom hit's lost health too).
• Lategame Upgrades: Locksmith (the fake locked door can be picked), speed upgrades, and longer days are handled.
• Modded weathers: Wesley's Weathers (by Magic_Wesley) has its own drain numbers for each of its weathers. Weather names are read through WeatherRegistry, which Wesley's Weathers and most other weather mods use. Other modded weathers count as clear weather; every weather's numbers can be changed in the config.
• Modded moons and interiors work. Phantom sounds only use vanilla monsters (modded monsters are skipped for now).

Telemetry (off by default)

If you turn on EnableTelemetry, the mod writes one CSV per game session to BepInEx/Sanity_Telemetry/: your sanity once a second, what changed it, and which symptoms happened. It stays on your computer: nothing is sent anywhere. The file includes in-game player names (yours, and teammates' where they matter, such as who carried loot in), so check it before sharing it with anyone. tools/analyze.py and tools/replay.py read these files (see tools/README.md).

Feedback and contributing

All of it is welcome: bug reports, suggestions, ideas, constructive criticism, advice, and questions about why the code does something. If you know C# or Unity modding and would like to review some of the code, that would be especially appreciated.

The best place is the issue tracker on GitHub: github.com/lowlightworks/Sanity/issues. When reporting a bug, the BepInEx log (BepInEx/LogOutput.log) and what you were doing help a lot.

Building from source

Needs the .NET 10 SDK.

1. Copy Config.Build.user.props.template to Config.Build.user.props and set your BepInEx folder (for a mod manager profile, the profile's BepInEx folder).
2. dotnet build -c Release. The DLL is copied into that BepInEx plugins folder automatically, and a Thunderstore zip is made in artifacts/thunderstore/.

Where to start reading the code: the comment at the top of src/Sanity/Plugin.cs.

Known limitations

• Phantom sounds and the Presence only imitate vanilla monsters.
• Phantom sounds and steps wait while you sprint (your own steps would drown them out); a long sprint can lose one.
• Lost time changes the clock, the sky and the music, but can still be missed.
• Balance is early and based on limited data.

The full list, with what's planned for each, is in docs/design.md.

License

MIT (see LICENSE).