diff --git a/src/player/crafting.ts b/src/player/crafting.ts
new file mode 100644
index 0000000..e49feb3
--- /dev/null
+++ b/src/player/crafting.ts
@@ -0,0 +1,102 @@
+/**
+ * Crafting System — Chemistry Engine Integration
+ *
+ * Combines items from inventory using the reaction engine.
+ * On success: consumes reagents, adds products.
+ * On failure: returns educational explanation of why it didn't work.
+ */
+
+import { ReactionEngine } from '../chemistry/engine';
+import type { ReactionConditions, ReactionData } from '../chemistry/types';
+import type { Inventory } from './inventory';
+
+/** What the player wants to combine */
+export interface CraftInput {
+  id: string;    // element symbol or compound id
+  count: number; // quantity to use
+}
+
+/** Result of a crafting attempt */
+export interface CraftResult {
+  success: boolean;
+  /** Products added to inventory (count may differ from reaction output if inventory full) */
+  products?: Array<{ id: string; count: number }>;
+  /** What was consumed from inventory */
+  consumedReactants?: CraftInput[];
+  /** Reaction data (for codex, description display) */
+  reaction?: ReactionData;
+  /** Why it failed (English) */
+  failureReason?: string;
+  /** Why it failed (Russian) */
+  failureReasonRu?: string;
+}
+
+/**
+ * Attempt to craft from inventory items.
+ *
+ * 1. Checks inventory has all reagents
+ * 2. Runs reaction engine (O(1) lookup + condition check)
+ * 3. On success: consumes reagents, adds products
+ * 4. On failure: returns educational reason
+ *
+ * Reagents are only consumed on success — failed attempts are free.
+ */
+export function craftFromInventory(
+  inventory: Inventory,
+  reactants: CraftInput[],
+  conditions?: Partial<ReactionConditions>,
+): CraftResult {
+  // Empty input
+  if (reactants.length === 0) {
+    return {
+      success: false,
+      failureReason: 'Select at least one substance to combine.',
+      failureReasonRu: 'Выберите хотя бы одно вещество для комбинирования.',
+    };
+  }
+
+  // 1. Check inventory has all reagents
+  for (const r of reactants) {
+    const have = inventory.getCount(r.id);
+    if (have < r.count) {
+      return {
+        success: false,
+        failureReason: `Not enough ${r.id} — have ${have}, need ${r.count}.`,
+        failureReasonRu: `Недостаточно ${r.id} — есть ${have}, нужно ${r.count}.`,
+      };
+    }
+  }
+
+  // 2. Run reaction engine
+  const result = ReactionEngine.react(
+    reactants.map(r => ({ id: r.id, count: r.count })),
+    conditions,
+  );
+
+  if (!result.success) {
+    return {
+      success: false,
+      failureReason: result.failureReason,
+      failureReasonRu: result.failureReasonRu,
+    };
+  }
+
+  // 3. Consume reagents
+  for (const r of reactants) {
+    inventory.removeItem(r.id, r.count);
+  }
+
+  // 4. Add products to inventory
+  const addedProducts: Array<{ id: string; count: number }> = [];
+  for (const p of result.products!) {
+    const added = inventory.addItem(p.id, p.count);
+    addedProducts.push({ id: p.id, count: added });
+  }
+
+  return {
+    success: true,
+    products: addedProducts,
+    consumedReactants: reactants,
+    reaction: result.reaction,
+  };
+}
diff --git a/tests/crafting.test.ts b/tests/crafting.test.ts
new file mode 100644
index 0000000..db4076e
--- /dev/null
+++ b/tests/crafting.test.ts
@@ -0,0 +1,189 @@
+/**
+ * Crafting System Tests — Phase 4.4
+ *
+ * Tests: crafting from inventory, reagent consumption,
+ * product addition, failure reasons, condition checks.
+ */
+
+import { describe, it, expect } from 'vitest';
+import { Inventory } from '../src/player/inventory';
+import { craftFromInventory, type CraftInput } from '../src/player/crafting';
+
+describe('craftFromInventory — success', () => {
+  it('crafts NaCl from Na + Cl', () => {
+    const inv = new Inventory();
+    inv.addItem('Na', 3);
+    inv.addItem('Cl', 2);
+
+    const inputs: CraftInput[] = [
+      { id: 'Na', count: 1 },
+      { id: 'Cl', count: 1 },
+    ];
+    const result = craftFromInventory(inv, inputs);
+
+    expect(result.success).toBe(true);
+    expect(result.products).toContainEqual({ id: 'NaCl', count: 1 });
+    // Reagents consumed
+    expect(inv.getCount('Na')).toBe(2);
+    expect(inv.getCount('Cl')).toBe(1);
+    // Product added
+    expect(inv.getCount('NaCl')).toBe(1);
+  });
+
+  it('returns reaction data on success', () => {
+    const inv = new Inventory();
+    inv.addItem('Na', 1);
+    inv.addItem('Cl', 1);
+
+    const result = craftFromInventory(inv, [
+      { id: 'Na', count: 1 },
+      { id: 'Cl', count: 1 },
+    ]);
+
+    expect(result.success).toBe(true);
+    expect(result.reaction).toBeDefined();
+    expect(result.reaction!.id).toBe('synth_nacl');
+  });
+
+  it('reports consumed reactants', () => {
+    const inv = new Inventory();
+    inv.addItem('Na', 5);
+    inv.addItem('Cl', 5);
+
+    const inputs: CraftInput[] = [
+      { id: 'Na', count: 1 },
+      { id: 'Cl', count: 1 },
+    ];
+    const result = craftFromInventory(inv, inputs);
+
+    expect(result.consumedReactants).toEqual(inputs);
+  });
+});
+
+describe('craftFromInventory — insufficient materials', () => {
+  it('fails when missing reagent', () => {
+    const inv = new Inventory();
+    inv.addItem('Na', 1);
+    // No Cl in inventory
+
+    const result = craftFromInventory(inv, [
+      { id: 'Na', count: 1 },
+      { id: 'Cl', count: 1 },
+    ]);
+
+    expect(result.success).toBe(false);
+    expect(result.failureReason).toContain('Cl');
+    // Na not consumed
+    expect(inv.getCount('Na')).toBe(1);
+  });
+
+  it('fails when not enough of a reagent', () => {
+    const inv = new Inventory();
+    inv.addItem('Na', 1);
+    inv.addItem('Cl', 1);
+
+    const result = craftFromInventory(inv, [
+      { id: 'Na', count: 5 }, // need 5, have 1
+      { id: 'Cl', count: 1 },
+    ]);
+
+    expect(result.success).toBe(false);
+    expect(result.failureReason).toContain('Na');
+  });
+});
+
+describe('craftFromInventory — unknown reaction', () => {
+  it('fails with educational reason for no known reaction', () => {
+    const inv = new Inventory(5000); // large capacity for heavy elements
+    inv.addItem('Fe', 5);
+    inv.addItem('Au', 5);
+
+    const result = craftFromInventory(inv, [
+      { id: 'Fe', count: 1 },
+      { id: 'Au', count: 1 },
+    ]);
+
+    expect(result.success).toBe(false);
+    expect(result.failureReason).toBeDefined();
+    expect(result.failureReason!.length).toBeGreaterThan(10); // educational reason
+    // Reagents not consumed
+    expect(inv.getCount('Fe')).toBe(5);
+    expect(inv.getCount('Au')).toBe(5);
+  });
+
+  it('explains noble gas inertness', () => {
+    const inv = new Inventory();
+    inv.addItem('He', 5);
+    inv.addItem('O', 5);
+
+    const result = craftFromInventory(inv, [
+      { id: 'He', count: 1 },
+      { id: 'O', count: 1 },
+    ]);
+
+    expect(result.success).toBe(false);
+    expect(result.failureReason).toContain('noble gas');
+  });
+});
+
+describe('craftFromInventory — conditions', () => {
+  it('fails when temperature requirement not met', () => {
+    const inv = new Inventory();
+    inv.addItem('Fe', 5);
+    inv.addItem('S', 5);
+
+    // Fe + S → FeS requires minTemp: 500
+    const result = craftFromInventory(inv, [
+      { id: 'Fe', count: 1 },
+      { id: 'S', count: 1 },
+    ]);
+
+    expect(result.success).toBe(false);
+    expect(result.failureReason).toContain('temperature');
+    // Reagents not consumed
+    expect(inv.getCount('Fe')).toBe(5);
+  });
+
+  it('succeeds when conditions are met', () => {
+    const inv = new Inventory();
+    inv.addItem('Fe', 5);
+    inv.addItem('S', 5);
+
+    const result = craftFromInventory(inv, [
+      { id: 'Fe', count: 1 },
+      { id: 'S', count: 1 },
+    ], { minTemp: 500 });
+
+    expect(result.success).toBe(true);
+    expect(result.products).toContainEqual({ id: 'FeS', count: 1 });
+    expect(inv.getCount('Fe')).toBe(4);
+    expect(inv.getCount('S')).toBe(4);
+  });
+});
+
+describe('craftFromInventory — edge cases', () => {
+  it('handles empty reactants list', () => {
+    const inv = new Inventory();
+    inv.addItem('Na', 5);
+
+    const result = craftFromInventory(inv, []);
+
+    expect(result.success).toBe(false);
+  });
+
+  it('handles inventory full for products', () => {
+    const inv = new Inventory(100, 2); // Only 2 slots
+    inv.addItem('Na', 1);
+    inv.addItem('Cl', 1);
+
+    // After crafting: Na consumed (slot freed), Cl consumed (slot freed), NaCl added
+    // This should work since slots are freed before products are added
+    const result = craftFromInventory(inv, [
+      { id: 'Na', count: 1 },
+      { id: 'Cl', count: 1 },
+    ]);
+
+    expect(result.success).toBe(true);
+    expect(inv.getCount('NaCl')).toBe(1);
+  });
+});