Elden Ring Build Advisor

Web tool for analyzing Elden Ring builds directly from a save file (.sl2). Reads the binary save, displays character stats and equipped gear with images and detailed tooltips, and shows accurate derived stats using exact game formulas — HP, FP, Stamina, Equip Load, Attack Rating, Damage Negation, Poise, Resistances, Flat Defense, Rune Level Calculator, and more.

Features

Save file upload — drag & drop or file picker for .sl2 (PC Steam only)
Character selection — card picker when the save has multiple active characters
Attributes panel — all 8 stats (VIG/MND/END/STR/DEX/INT/FAI/ARC) with proportional bars, softcap ticks, and info tooltips explaining what each stat does
Derived stats (sub-tabbed: Body | Attack | Defense) — info tooltips on every stat explaining what it does, how it scales, and its softcaps
- Body: HP, FP, Stamina, Equip Load with exact piecewise interpolation formulas; Rune Level Calculator (exact game formula: floor((max(0, (L-11)*0.02) + 0.1) * (L+81)^2 + 1))
- Attack: Estimated AR per weapon with 2H STR toggle (×1.5), off-hand AR, spell scaling (staves/seals), weapon passives with ARC scaling, configurable buffs (Golden Vow, Flame Grant Me Strength, etc.)
- Defense: Damage Negation % for equipped armor (with buff indicators), Guard Boost for shields, Poise (color breakpoints), Resistances (Immunity, Robustness, Focus, Vitality — flat values, exact game formulas), Discovery
Talisman effects — ~35 talismans with numeric effects: HP/FP/Stamina/Equip Load bonuses, elemental damage %, defense %, skill/spell power, guard boost, poise, resistances, discovery
Great Rune & Physick — toggle Rune Arc and Flask of Wondrous Physick to see stat changes in real time
Buff system — configurable damage/defense buffs (Golden Vow, Flame Grant Me Strength, Howl of Shabriri, etc.) with multiplicative stacking
Equipment grid — weapons (Left Hand / Right Hand), full armor (Head / Chest / Arms / Legs) and 4 talismans with fanapis images and SVG placeholders per category
Item tooltips on hover — full stats for each equipped item:
- Weapons: Estimated AR per damage type (bars) with per-stat scaling breakdown (e.g. DEX D 34 → +82), requirement check with penalty warning, ARC-scaled passive effects (Bleed, Frost, Poison), Ash of War skill + FP cost
- Armor: Damage Negation per type (8 values, float precision), Poise, Resistances, armor efficiency ratio (phys def / weight)
- Shields: Guard Boost (stability) + guard negation per element
- Talismans: numeric effects (HP%, Stamina%, etc.) or text description
- Weight for all items
Inventory tooltips — AR estimation for inventory weapons using character stats, requirement met/unmet styling, ARC-scaled passives
Full inventory — 14 tabs: Weapons / Armor / Talismans / Spells / Spirits / Ashes of War / Consumables / Materials / Upgrades / Tears / Ammo / Key Items / Cookbooks / Multiplayer — with name search and type filter per tab
Build recommender — 30 curated community builds matched to your character's stats using weighted scoring (stat similarity, level range, inventory cross-check). Expandable cards show complete builds: weapons, shields, armor, talismans, ashes of war, spells, stat comparison (yours vs ideal), and tips. Covers all major archetypes including DLC weapon classes
Matchmaking calculator — co-op and invasion level/weapon upgrade ranges

Layout

┌─────────────────────────────────────────────────────────────────────┐
│  ← Back   ZHYAK                         Level 68 · 33h 14m   ↓ PNG │
├──────────────────┬──────────────────────────────────────────────────┤
│  ATTRIBUTES      │  EQUIPMENT                                        │
│  VIG 34 ████     │  Weapons                                          │
│  MND 17 ██       │   Left Hand      Right Hand                       │
│  END 18 ██       │   [LH1][LH2][LH3] [RH1][RH2][RH3]               │
│  STR 18 ██       │                                                   │
│  DEX 34 ████     │  Armor                                            │
│  INT  7 █        │   [Head][Chest][Arms][Legs]                       │
│  FAI  8 █        │                                                   │
│  ARC 11 █        │  Talismans                                        │
│                  │   [T1][T2][T3][T4]                                │
│  HP   1193       ├──────────────────────────────────────────────────┤
│  FP    132       │  INVENTORY                                        │
│  STA   120       │  [Weapons][Armor][Talisms.][Spells][Spirits]...   │
│  LOAD 55.6/72.0  │  🔍 Search by name...  [All types ▼]             │
│  ATK   368       │  [item grid with images and tooltips]             │
│  DEF  27.9%      │                                                   │
└──────────────────┴──────────────────────────────────────────────────┘

Tech stack

Backend

Technology	Role
Node.js 22 + TypeScript 5.7	Runtime and language
Express 4	HTTP server
Multer 2	`.sl2` file upload (memoryStorage)
ts-node-dev	Dev server with hot reload
Jest 30 + ts-jest	Tests (134 tests)

Frontend

Technology	Role
React 19 + TypeScript 5.7	UI
Vite 6	Bundler and dev server
CSS Modules	Per-component styles
Google Fonts (EB Garamond + Cormorant Garamond)	Thematic typography

Running the project

Option 1 — Docker Compose (recommended)

git clone https://github.com/tu-usuario/elden-ring-build-advisor.git
cd elden-ring-build-advisor
docker compose up

Backend: http://localhost:3001
Frontend: http://localhost:5173

Option 2 — Local (no Docker)

# Backend
cd backend
npm install
npm run dev        # http://localhost:3001

# Frontend (separate terminal)
cd frontend
npm install
npm run dev        # http://localhost:5173

Sync item data

The JSONs in backend/src/data/ are committed and ready to use. To regenerate them from upstream sources:

cd backend
npm run sync-data       # download from fanapis.com + map with real game IDs
npm run patch-armor     # apply float precision from EquipParamProtector (game data)
npm run audit           # verify data quality (exits with code 1 if critical bugs found)

Architecture

elden-ring-build-advisor/
├── backend/
│   ├── src/
│   │   ├── parser/        # Binary .sl2 reader (BND4, stats, offsets)
│   │   ├── inventory/     # ChrAsm2: equipped gear + full inventory
│   │   ├── items/         # ItemStore, AR advisor, types
│   │   ├── data/          # Item JSONs (weapons, armors, talismans, spells…)
│   │   └── index.ts       # Express app + REST endpoints
│   └── scripts/
│       ├── sync-data.ts           # Download and normalize data from fanapis.com
│       ├── patch-armor-precision.ts  # Apply float defense values from game's EquipParamProtector
│       └── audit-data.ts          # Data quality audit (duplicates, zero values, type errors)
└── frontend/
    └── src/
        ├── components/
        │   ├── BuildPage/         # Main layout
        │   ├── StatsPanel/        # 8 attributes
        │   ├── DerivedStatsPanel/ # Sub-tabs: Body | Attack | Defense (exact game formulas)
        │   ├── EquipmentGrid/     # Weapons + armor + talismans
        │   ├── ItemSlot/          # Slot with image, upgrade badge, infusion badge
        │   ├── ItemTooltip/       # Hover tooltip: AR, defense, poise, resistances, guard boost, skill
        │   ├── InventoryTooltip/  # Hover tooltip for inventory items
        │   ├── InventoryPanel/    # Full inventory with search and type filter
        │   ├── AdvisorPanel/      # 30 community builds ranked by stat match + Next Caps optimizer
        │   ├── MatchmakingCalc/  # Co-op & Invasion range calculator
        │   ├── CharacterSelect/   # Character card picker
        │   └── UploadPage/        # .sl2 drop zone
        ├── hooks/
        │   ├── useMountAnimation.ts   # Bar animation on mount
        │   └── useTooltipPosition.ts  # Viewport-aware tooltip flip
        └── utils/
            ├── arCalc.ts              # AR estimation, flat defense, spell scaling, passive buildup
            ├── buildMatcher.ts        # Build recommender: weighted scoring (stat/level/inventory)
            ├── talismanEffects.ts     # Numeric effects for ~35 known talismans
            ├── buffEffects.ts         # Buff system (Golden Vow, Flame Grant Me Strength, etc.)
            ├── greatRuneEffects.ts    # Great Rune stat bonuses
            └── crystalTearEffects.ts  # Crystal Tear (Physick) bonuses

How the `.sl2` is read

The Elden Ring save file uses FromSoftware's BND4 container format. The parser reverse-engineers:

BND4 header → locates character slots
findStats() → pattern search by attribute sum (level + 79) to locate the 8 stats in slot data
ChrAsm2 (vigor_offset + 0x310) → 96-byte struct with equipment gaitem_handles
ga_items lookup → handles resolved against the slot's item table to get real IDs
ID decoding:
- Weapons: baseId = floor(item_id / 100) * 100, upgradeLevel = item_id % 100
- Armor: baseId = item_id XOR 0x10000000
- Talismans: baseId = handle XOR 0xA0000000 (direct, no ga_items)

API Endpoints

Method	Route	Description
`GET`	`/health`	Server health + item counts
`POST`	`/api/parse`	Parse `.sl2` → stats + gear + optional full inventory
`GET`	`/api/items/weapons`	List weapons with optional filters
`GET`	`/api/items/armors`	List armors
`GET`	`/api/items/talismans`	List talismans
`GET`	`/api/items/spells`	List spells
`GET`	`/api/builds`	30 curated community build templates
`POST`	`/api/advisor`	Weapon recommendations by character stats

# Parse a save file
curl -X POST http://localhost:3001/api/parse \
  -F "savefile=@/path/to/ER0000.sl2"

# Full inventory
curl -X POST "http://localhost:3001/api/parse?inventory=true" \
  -F "savefile=@/path/to/ER0000.sl2"

# Advisor
curl -X POST http://localhost:3001/api/advisor \
  -H "Content-Type: application/json" \
  -d '{"vigor":34,"mind":17,"endurance":18,"strength":18,"dexterity":34,"intelligence":7,"faith":8,"arcane":11}'

Tests

cd backend && npm test   # 134 tests — parser, inventory scanner, item store, advisor

Data sources

File	Source
`weapons.json` (306)	fanapis.com — base stats + images
`armors.json` (568)	fanapis.com — base data; defense values patched with float precision (see below)
`talismans.json` (87)	fanapis.com
`spells.json` (169)	fanapis.com
`shields.json`, `ashes.json`, `spirits.json`, `consumables.json`	fanapis.com
`gameIds.json`	Deskete/EldenRingResources — real weapon IDs
`armorIds.json`	ClayAmore/ER-Save-Editor — EquipParamProtector IDs
`talismanIds.json`	ClayAmore/ER-Save-Editor — EquipParamAccessory IDs
`gemIds.json`	ClayAmore/ER-Save-Editor — Ash of War IDs
Armor defense floats + poise	jerpdoesgames/EldenRingArmorOptimizer — extracted from `regulation.bin → EquipParamProtector`
Derived stat formulas	Elden Ring community (piecewise interpolation, reverse-engineered)

Armor data precision

fanapis stores defense values as integers. The patch-armor script overlays float values extracted from the game's EquipParamProtector param (via EldenRingArmorOptimizer):

550 / 568 armors have float precision (e.g. strike: 5.4 instead of 5)
Also adds poise and resistances (immunity, robustness, focus, vitality) — not available in fanapis
18 unmatched (6 Shadow of the Erdtree DLC pieces not yet in the optimizer, ~12 obscure items with near-zero stats) — keep integer approximations from fanapis

Credits & Acknowledgments

This project wouldn't be possible without the incredible Elden Ring community and their reverse-engineering work:

Resource	Author / Project	Used for
Elden Ring Fan API	fanapis.com	Item data (weapons, armors, talismans, spells, shields, ashes, spirits, consumables) + images
EldenRingResources	Deskete	Real weapon IDs (`gameIds.json`) extracted from game data
ER-Save-Editor	ClayAmore	Armor IDs (EquipParamProtector), Talisman IDs (EquipParamAccessory), Ash of War IDs (EquipParamGem), .sl2 binary format reference
EldenRingArmorOptimizer	jerpdoesgames	Float-precision defense values, poise, and resistance data extracted from `regulation.bin → EquipParamProtector`
Elden Ring Wiki (Fextralife)	Fextralife community	Fallback item images, formula verification, softcap reference
Elden Ring community	Various contributors	Reverse-engineered formulas: HP/FP/Stamina/Equip Load piecewise interpolation, AR scaling curves, flat defense formulas, resistance formulas, rune cost formula, matchmaking ranges
Google Fonts	Google	EB Garamond (display) + Cormorant Garamond (UI headings)

Built with Claude Code by Anthropic.

Known limitations

Item images depend on fanapis.com CDN availability; SVG placeholders shown on failure
Estimated AR in tooltips and advisor is approximate (based on community reverse-engineering of stat scaling curves); may differ slightly from in-game values
Console saves (PS4/PS5/Xbox) are not supported — PC Steam .sl2 only
18 armor pieces have integer defense values instead of floats (see Data sources above)

License

MIT — This project is not affiliated with FromSoftware or Bandai Namco.

Name		Name	Last commit message	Last commit date
Latest commit History 33 Commits
backend		backend
frontend		frontend
.env.example		.env.example
.gitignore		.gitignore
AGENTS.md		AGENTS.md
README.md		README.md
docker-compose.yml		docker-compose.yml

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Elden Ring Build Advisor

Features

Layout

Tech stack

Backend

Frontend

Running the project

Option 1 — Docker Compose (recommended)

Option 2 — Local (no Docker)

Sync item data

Architecture

How the `.sl2` is read

API Endpoints

Tests

Data sources

Armor data precision

Credits & Acknowledgments

Known limitations

License

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Elden Ring Build Advisor

Features

Layout

Tech stack

Backend

Frontend

Running the project

Option 1 — Docker Compose (recommended)

Option 2 — Local (no Docker)

Sync item data

Architecture

How the .sl2 is read

API Endpoints

Tests

Data sources

Armor data precision

Credits & Acknowledgments

Known limitations

License

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How the `.sl2` is read