S2Tweaker — S.T.A.L.K.E.R. 2 Mod Generator

A Windows GUI tool that builds a personal tweak mod (.pak) for S.T.A.L.K.E.R. 2: Heart of Chornobyl from sliders and checkboxes — no modding knowledge needed.

Open source (MIT). Everything in this repo was written by Claude (Anthropic's AI) — the project owner can't code and considers this a working concept for people who can: fork it, improve it, find bugs, build on it. Everyone is free to use it. This README tells you everything you need.

What it does

• Reads the vanilla values from YOUR installed game version (extracts the needed .cfg.bin GameData from pakchunk0 and decodes it) — so multiplier tweaks stay correct after game patches.
• Generates {bpatch} config patches (the official patch system since game version 1.6): only the values you change are written; everything at "(vanilla)" is untouched and cannot conflict with other mods.
• Packs them with repak into zzz_<Name>_P.pak (pak V8B, mount point ../../../) — into an output folder, or directly into ~mods.
• Fully portable: settings, cache and output live next to the exe.

41 tweaks: health/stamina/regen, per-action stamina costs, fall damage, movement speed, jump height, carry weight + penalty threshold, item weights per category, player/NPC/mutant damage & health, headshots, explosions, durability, jamming, spread, recoil, scoped sway, breath hold, anomaly/ radiation/bleeding, hunger/sleep rates, trader prices & min. durability, repair/upgrade costs, quest rewards.

How it works (the important mechanics)

Layer	Details
Vanilla data	repak unpack of pakchunk0-Windows.pak (only ~10 needed GameData files), then .cfg.bin → text via the vendored decoder (s2tweaker/vendor_bin2cfg.py). Cached in cache/vanilla-<pakSize>-s<schema>/; a game update changes the fingerprint → automatic re-extraction.
Parsing	cfgparse.py parses GSC's cfg text format (Name : struct.begin {refkey=...} … struct.end) into a tree; refkey inheritance chains are resolved to get effective vanilla values.
Patch output	emit.py writes {bpatch} structs. Patch files follow the proven convention <BaseCfg>/<BaseCfg>_patch_<Mod>.cfg under Stalker2/Content/GameLite/GameData/.
Packing	pakio.py stages the files and calls the bundled tools/repak.exe (defaults are exactly what the game wants: V8B, mount ../../../, uncompressed).
Key game files	ObjPrototypes (player + mutants), ItemPrototypes, TradePrototypes, DifficultyPrototypes (per-difficulty multiplier groups), EffectPrototypes (overweight effects), FloatProviderPrototypes (scope-sway constant — patched instead of the sway effects so offset-aiming keeps working), WeaponData/* (damage, wear, spread, recoil), CoreVariables (repair costs, stamina drain), ObjWeightParamsPrototypes (carry weight), ObjHoldBreathParamsPrototypes.

Deep research notes with sources, vanilla values and risk analysis: docs/SPEC.md.

Project structure

main.py                 entry point (also the PyInstaller entry)
s2tweaker/
  gui.py                customtkinter GUI (dark, English)
  tweaks.py             Settings dataclass + one builder per feature
  gamedata.py           extraction pipeline, parsing, inheritance resolution
  cfgparse.py           GSC cfg text parser
  emit.py               {bpatch} cfg writer
  pakio.py              repak wrapper (pack/unpack)
  game.py               game folder auto-detection (Steam/GOG/Xbox)
  vendor_bin2cfg.py     cfg.bin → cfg decoder (vendored, public domain)
tools/repak.exe         pak tool (MIT/Apache-2.0, by trumank)
docs/SPEC.md            research: every tweak's mechanism + sources
release/README.txt      end-user readme shipped with the exe
test_generate.py        end-to-end dev test (builds a test pak)
build.bat               builds dist/S2Tweaker.exe

Building from source

pip install -r requirements.txt
python main.py          # run the GUI directly
build.bat               # or build dist/S2Tweaker.exe

Python 3.12+ recommended. For development, the GUI prefers a local vanilla/Stalker2/Content/GameLite/GameData/ folder if present (create it by running the tool once and copying the contents of cache/vanilla-*/), else it extracts from the game on "Confirm & load game data". python test_generate.py builds a test pak with many tweaks active.

Adding a new tweak (3 steps)

1. tweaks.py — add a field to Settings (default = vanilla), then write/extend a builder that emits a {bpatch} dict only when the value deviates (_neq(...)), using vanilla values read via gd.resolve(...). Add a line to summarize().
2. gamedata.py — if you need a GameData file that isn't extracted yet, add it to NEEDED_FILES and bump CACHE_SCHEMA (this invalidates old caches automatically).
3. gui.py — add a self._slider(...) / self._check(...) row in _build_body() and map it in _collect().

Golden rule: patch only what the user changed, compute from vanilla values of the installed version, and never hardcode game numbers.

Legal / contributor notes

• Never commit or upload extracted game files (vanilla/, cache/) — that content is copyrighted by GSC Game World. .gitignore covers this.
• Tool code is MIT (see LICENSE). Bundled: repak (MIT/Apache-2.0), cfg.bin decoder based on public-domain code by joric/sdwvit/thexii.
• Known limits: DLC items aren't covered by the per-item weight slider; iron-sight sway is animation-driven (not cfg-tweakable); the in-game "Custom Rules" difficulty overlaps some multipliers (precedence untested).

Credits

• repak by trumank
• bin2cfg by joric, S2CfgToJSON by sdwvit (+ thexii)
• The S.T.A.L.K.E.R. 2 modding community for documenting the {bpatch} system, and GSC Game World for the game.