diff --git a/src/__tests__/modules.test.ts b/src/__tests__/modules.test.ts
index 302a1f5..8c2dbc6 100644
--- a/src/__tests__/modules.test.ts
+++ b/src/__tests__/modules.test.ts
@@ -54,7 +54,11 @@ describe('module system', () => {
     `;
     fs.writeFileSync(questPath, quest);
 
-    const interpreter = QuestLang.interpret(quest, questPath);
+    const host = {
+      readFile: (file: string) => fs.readFileSync(file, 'utf8'),
+      resolve: (fromFile: string, spec: string) => path.resolve(path.dirname(fromFile), spec),
+    } as const;
+    const interpreter = QuestLang.interpret(quest, questPath, host);
     const validation = interpreter.validate();
     expect(validation.isValid).toBe(true);
   });
@@ -100,7 +104,11 @@ describe('module system', () => {
       конец;
     `);
 
-    const interpreter = QuestLang.interpret(fs.readFileSync(qPath, 'utf8'), qPath);
+    const host = {
+      readFile: (file: string) => fs.readFileSync(file, 'utf8'),
+      resolve: (fromFile: string, spec: string) => path.resolve(path.dirname(fromFile), spec),
+    } as const;
+    const interpreter = QuestLang.interpret(fs.readFileSync(qPath, 'utf8'), qPath, host);
     const validation = interpreter.validate();
     expect(validation.isValid).toBe(true);
   });
@@ -133,7 +141,11 @@ describe('module system', () => {
     `;
     fs.writeFileSync(questPath, quest);
 
-    const interpreter = QuestLang.interpret(quest, questPath);
+    const host = {
+      readFile: (file: string) => fs.readFileSync(file, 'utf8'),
+      resolve: (fromFile: string, spec: string) => path.resolve(path.dirname(fromFile), spec),
+    } as const;
+    const interpreter = QuestLang.interpret(quest, questPath, host);
     const validation = interpreter.validate();
     expect(validation.isValid).toBe(false);
     expect(validation.errors.some(e => e.includes('non-existent') || e.includes('not exported'))).toBe(true);
diff --git a/src/cli.ts b/src/cli.ts
index 88fe7b8..6957a80 100644
--- a/src/cli.ts
+++ b/src/cli.ts
@@ -3,6 +3,7 @@
 import type { QuestInterpreter } from '.';
 import type { InitialNode, NodeDefinition } from './ast.js';
 import fs from 'node:fs';
+import path from 'node:path';
 import process from 'node:process';
 import * as p from '@clack/prompts';
 import { QuestLang } from '.';
@@ -122,7 +123,11 @@ class ClackCLI {
       spinner.start('Loading quest...');
 
       const source = this.readFile(filename);
-      const interpreter = QuestLang.interpret(source, filename);
+      const host = {
+        readFile: (file: string) => fs.readFileSync(file, 'utf8'),
+        resolve: (fromFile: string, spec: string) => path.resolve(path.dirname(fromFile), spec),
+      } as const;
+      const interpreter = QuestLang.interpret(source, filename, host);
 
       // Validate first
       const validation = interpreter.validate();
@@ -237,7 +242,11 @@ class ClackCLI {
       spinner.start('Validating quest...');
 
       const source = this.readFile(filename);
-      const validation = QuestLang.validate(source, filename);
+      const host = {
+        readFile: (file: string) => fs.readFileSync(file, 'utf8'),
+        resolve: (fromFile: string, spec: string) => path.resolve(path.dirname(fromFile), spec),
+      } as const;
+      const validation = QuestLang.validate(source, filename, host);
 
       if (validation.isValid) {
         spinner.stop('✅ Validation completed');
@@ -268,7 +277,11 @@ class ClackCLI {
       spinner.start('Analyzing quest...');
 
       const source = this.readFile(filename);
-      const interpreter = QuestLang.interpret(source, filename);
+      const host = {
+        readFile: (file: string) => fs.readFileSync(file, 'utf8'),
+        resolve: (fromFile: string, spec: string) => path.resolve(path.dirname(fromFile), spec),
+      } as const;
+      const interpreter = QuestLang.interpret(source, filename, host);
       const questInfo = interpreter.getQuestInfo();
 
       spinner.stop('✅ Analysis completed');
diff --git a/src/index.ts b/src/index.ts
index b6ffd5c..a60aaef 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,5 +1,6 @@
 import type { QuestProgram } from './ast';
 import { QuestInterpreter } from './interpreter';
+import type { ModuleHost } from './module-loader';
 import { Lexer } from './lexer';
 import { Parser } from './parser';
 
@@ -21,17 +22,17 @@ export class QuestLang {
   /**
    * Create interpreter from source code
    */
-  public static interpret(source: string, filePath?: string): QuestInterpreter {
+  public static interpret(source: string, filePath?: string, host?: ModuleHost): QuestInterpreter {
     const ast = this.parse(source);
-    return new QuestInterpreter(ast, filePath);
+    return new QuestInterpreter(ast, filePath, host);
   }
 
   /**
    * Validate QuestLang source code
    */
-  public static validate(source: string, filePath?: string): { isValid: boolean; errors: string[] } {
+  public static validate(source: string, filePath?: string, host?: ModuleHost): { isValid: boolean; errors: string[] } {
     try {
-      const interpreter = this.interpret(source, filePath);
+      const interpreter = this.interpret(source, filePath, host);
       return interpreter.validate();
     }
     catch (error) {
@@ -45,5 +46,6 @@ export class QuestLang {
 
 export * from './ast';
 export { QuestInterpreter } from './interpreter';
+export type { ModuleHost } from './module-loader';
 export { Lexer } from './lexer';
 export { Parser } from './parser';
diff --git a/src/interpreter.ts b/src/interpreter.ts
index 4f7e3ae..1291e7c 100644
--- a/src/interpreter.ts
+++ b/src/interpreter.ts
@@ -6,8 +6,8 @@ import type {
   OptionChoice,
   QuestProgram,
 } from './ast';
-import path from 'node:path';
 import { ModuleLoader } from './module-loader';
+import type { ModuleHost } from './module-loader';
 
 /**
  * Runtime state of the quest
@@ -45,7 +45,7 @@ export class QuestInterpreter {
   private currentState: QuestState;
   private moduleLoader?: ModuleLoader;
 
-  constructor(program: QuestProgram, questFilePath?: string) {
+  constructor(program: QuestProgram, questFilePath?: string, host?: ModuleHost) {
     this.program = program;
     this.currentState = {
       currentNode: program.graph.start,
@@ -54,8 +54,8 @@ export class QuestInterpreter {
     };
 
     // Initialize module loader if imports present and quest file path provided
-    if (questFilePath && program.imports && program.imports.length > 0) {
-      this.moduleLoader = new ModuleLoader(path.dirname(questFilePath));
+    if (questFilePath && host && program.imports && program.imports.length > 0) {
+      this.moduleLoader = new ModuleLoader(host);
       // Load modules
       this.moduleLoader.loadQuest(questFilePath);
     }
diff --git a/src/module-loader.ts b/src/module-loader.ts
index 53145f0..074e433 100644
--- a/src/module-loader.ts
+++ b/src/module-loader.ts
@@ -1,9 +1,12 @@
 import type { ImportNode, ModuleNode, QuestProgram } from './ast';
-import fs from 'node:fs';
-import path from 'node:path';
 import { Lexer } from './lexer';
 import { Parser } from './parser';
 
+export interface ModuleHost {
+  readFile(file: string): string;
+  resolve(fromFile: string, specifier: string): string;
+}
+
 export enum VisitState {
   Unvisited,
   Visiting,
@@ -23,17 +26,17 @@ export class ModuleLoader {
   private byFile = new Map<string, LoadedModule>();
   private visit = new Map<string, VisitState>();
 
-  constructor(private baseDir: string) {}
+  constructor(private host: ModuleHost) {}
 
   public loadQuest(questFile: string): { program: QuestProgram; modules: LoadedModule[] } {
-    const source = fs.readFileSync(questFile, 'utf8');
+    const source = this.host.readFile(questFile);
     const program = this.parseQuest(source);
 
     // Parse imports (if any)
     const imports: ImportNode[] = program.imports || [];
 
     for (const imp of imports) {
-      const abs = path.resolve(path.dirname(questFile), imp.modulePath);
+      const abs = this.host.resolve(questFile, imp.modulePath);
       this.dfsParse(abs);
     }
 
@@ -52,14 +55,14 @@ export class ModuleLoader {
     this.visit.set(file, VisitState.Visiting);
 
     if (!this.byFile.has(file)) {
-      const src = fs.readFileSync(file, 'utf8');
+      const src = this.host.readFile(file);
       const ast = this.parseModule(src, file);
       this.byFile.set(file, { name: ast.name, file, ast });
 
       // Follow module's own imports (if any)
       const ownImports = ast.imports || [];
       for (const imp of ownImports) {
-        const dep = path.resolve(path.dirname(file), imp.modulePath);
+        const dep = this.host.resolve(file, imp.modulePath);
         this.dfsParse(dep);
       }
     }