diff --git a/src/graph/projectGraph.ts b/src/graph/projectGraph.ts
new file mode 100644
index 0000000..f323fed
--- /dev/null
+++ b/src/graph/projectGraph.ts
@@ -0,0 +1,373 @@
+import * as fs from 'node:fs';
+import * as path from 'node:path';
+import { AstAnalyzer } from '../analyzer/astAnalyzer';
+import {
+  AffectedCaller,
+  AffectedRoute,
+  AffectedSymbol,
+  FileAnalysis,
+  ImpactAnalysis,
+  SymbolInfo
+} from '../types';
+
+export class ProjectGraph {
+  private workspaceRoot: string;
+  private fileAnalyses = new Map<string, FileAnalysis>();
+  private fileDependents = new Map<string, Set<string>>(); // targetFile -> Set of files that import it
+  private fileDependencies = new Map<string, Set<string>>(); // sourceFile -> Set of files it imports
+  private pathAliases = new Map<string, string>(); // alias prefix -> target dir
+
+  constructor(workspaceRoot: string) {
+    this.workspaceRoot = workspaceRoot;
+    this.loadTsConfigAliases();
+  }
+
+  private loadTsConfigAliases(): void {
+    const tsconfigPath = path.join(this.workspaceRoot, 'tsconfig.json');
+    if (!fs.existsSync(tsconfigPath)) return;
+
+    try {
+      const raw = fs.readFileSync(tsconfigPath, 'utf8');
+      // Strip comments
+      const cleaned = raw.replace(/\/\*[\s\S]*?\*\/|\/\/.*/g, '');
+      const parsed = JSON.parse(cleaned);
+      const paths = parsed.compilerOptions?.paths;
+      const baseUrl = parsed.compilerOptions?.baseUrl || '.';
+
+      if (paths && typeof paths === 'object') {
+        for (const [aliasPattern, targetList] of Object.entries(paths)) {
+          if (Array.isArray(targetList) && targetList.length > 0) {
+            const cleanAlias = aliasPattern.replace(/\*$/, '');
+            const cleanTarget = (targetList[0] as string).replace(/\*$/, '');
+            const resolvedTarget = path.resolve(this.workspaceRoot, baseUrl, cleanTarget);
+            this.pathAliases.set(cleanAlias, resolvedTarget);
+          }
+        }
+      }
+    } catch {
+      // Ignore tsconfig parsing errors
+    }
+  }
+
+  /**
+   * Scans all code files in the workspace and builds the dependency graph.
+   */
+  public async buildGraph(filterFiles?: string[]): Promise<void> {
+    const filesToScan = filterFiles ?? this.findSourceFiles(this.workspaceRoot);
+
+    for (const file of filesToScan) {
+      const analysis = AstAnalyzer.analyzeFile(file);
+      this.fileAnalyses.set(file, analysis);
+    }
+
+    // Resolve dependencies and construct reverse dependents graph
+    for (const [sourceFile, analysis] of this.fileAnalyses.entries()) {
+      const deps = new Set<string>();
+
+      for (const imp of analysis.imports) {
+        const resolved = this.resolveImportPath(sourceFile, imp.source);
+        if (resolved) {
+          deps.add(resolved);
+          imp.resolvedPath = resolved;
+
+          let reverseSet = this.fileDependents.get(resolved);
+          if (!reverseSet) {
+            reverseSet = new Set<string>();
+            this.fileDependents.set(resolved, reverseSet);
+          }
+          reverseSet.add(sourceFile);
+        }
+      }
+
+      this.fileDependencies.set(sourceFile, deps);
+    }
+  }
+
+  public resolveImportPath(currentFile: string, importSource: string): string | null {
+    // 1. Relative import
+    if (importSource.startsWith('.')) {
+      const dir = path.dirname(currentFile);
+      const targetCandidate = path.resolve(dir, importSource);
+      return this.tryResolveFileExtensions(targetCandidate);
+    }
+
+    // 2. Check path aliases (e.g. "@/..." or "~/...")
+    for (const [alias, targetBase] of this.pathAliases.entries()) {
+      if (importSource.startsWith(alias)) {
+        const remainder = importSource.substring(alias.length);
+        const resolvedCandidate = path.resolve(targetBase, remainder);
+        return this.tryResolveFileExtensions(resolvedCandidate);
+      }
+    }
+
+    return null;
+  }
+
+  private tryResolveFileExtensions(basePath: string): string | null {
+    const extensions = ['.ts', '.tsx', '.js', '.jsx', '.mjs', '.cjs'];
+
+    // Direct file match
+    if (fs.existsSync(basePath) && fs.statSync(basePath).isFile()) {
+      return basePath;
+    }
+
+    // Match with extension
+    for (const ext of extensions) {
+      const candidate = `${basePath}${ext}`;
+      if (fs.existsSync(candidate) && fs.statSync(candidate).isFile()) {
+        return candidate;
+      }
+    }
+
+    // Match directory index file
+    if (fs.existsSync(basePath) && fs.statSync(basePath).isDirectory()) {
+      for (const ext of extensions) {
+        const indexCandidate = path.join(basePath, `index${ext}`);
+        if (fs.existsSync(indexCandidate) && fs.statSync(indexCandidate).isFile()) {
+          return indexCandidate;
+        }
+      }
+    }
+
+    return null;
+  }
+
+  private findSourceFiles(dir: string, fileList: string[] = []): string[] {
+    if (!fs.existsSync(dir)) return fileList;
+
+    const ignoredDirs = new Set([
+      'node_modules',
+      '.git',
+      'dist',
+      'out',
+      '.next',
+      '.turbo',
+      'coverage',
+      'build'
+    ]);
+
+    const entries = fs.readdirSync(dir, { withFileTypes: true });
+    for (const entry of entries) {
+      const fullPath = path.join(dir, entry.name);
+      if (entry.isDirectory()) {
+        if (!ignoredDirs.has(entry.name) && !entry.name.startsWith('.')) {
+          this.findSourceFiles(fullPath, fileList);
+        }
+      } else if (entry.isFile()) {
+        if (/\.(ts|tsx|js|jsx|mjs|cjs)$/.test(entry.name) && !entry.name.endsWith('.d.ts')) {
+          fileList.push(fullPath);
+        }
+      }
+    }
+
+    return fileList;
+  }
+
+  public getAnalysis(filePath: string): FileAnalysis | undefined {
+    return this.fileAnalyses.get(filePath);
+  }
+
+  public getDependents(filePath: string): Set<string> {
+    return this.fileDependents.get(filePath) || new Set();
+  }
+
+  public isTestFile(filePath: string): boolean {
+    const normalized = filePath.replace(/\\/g, '/');
+    return (
+      normalized.includes('.test.') ||
+      normalized.includes('.spec.') ||
+      normalized.includes('/__tests__/') ||
+      normalized.includes('/tests/')
+    );
+  }
+
+  /**
+   * Computes the change impact across the codebase given a map of changed files and lines.
+   */
+  public computeImpact(fileChangedLines: Map<string, number[]>): ImpactAnalysis {
+    const changedFiles = Array.from(fileChangedLines.keys());
+    const affectedFilesSet = new Set<string>();
+    const affectedCallers: AffectedCaller[] = [];
+    const affectedRoutes: AffectedRoute[] = [];
+    const changedSymbolsList: AffectedSymbol[] = [];
+
+    // Collect all test files in the workspace for test coverage check
+    const allTestFiles = Array.from(this.fileAnalyses.keys()).filter((f) => this.isTestFile(f));
+
+    for (const [changedFile, lineNumbers] of fileChangedLines.entries()) {
+      const analysis = this.fileAnalyses.get(changedFile);
+      if (!analysis) continue;
+
+      // Find changed symbols in this file
+      const touchedSymbols = AstAnalyzer.findSymbolsAtLines(analysis.symbols, lineNumbers);
+
+      for (const sym of touchedSymbols) {
+        const callers = this.findCallersForSymbol(sym, changedFile, allTestFiles);
+        const isApiRoute =
+          sym.kind === 'api_route' ||
+          (analysis.hasApiRoute &&
+            /^(GET|POST|PUT|DELETE|PATCH)$/i.test(sym.name));
+
+        changedSymbolsList.push({
+          symbolName: sym.name,
+          kind: sym.kind,
+          filePath: changedFile,
+          callers,
+          isApiRoute
+        });
+
+        for (const caller of callers) {
+          affectedCallers.push(caller);
+          affectedFilesSet.add(caller.filePath);
+        }
+      }
+
+      // Add direct and transitive dependents
+      const dependents = this.getTransitiveDependents(changedFile);
+      for (const dep of dependents) {
+        affectedFilesSet.add(dep);
+        const depAnalysis = this.fileAnalyses.get(dep);
+        if (depAnalysis && depAnalysis.hasApiRoute) {
+          for (const route of depAnalysis.apiRoutes) {
+            affectedRoutes.push({
+              routePath: route.path,
+              method: route.method,
+              filePath: dep,
+              line: route.line
+            });
+          }
+        }
+      }
+
+      // Check if the changed file itself has API routes
+      if (analysis.hasApiRoute) {
+        for (const route of analysis.apiRoutes) {
+          affectedRoutes.push({
+            routePath: route.path,
+            method: route.method,
+            filePath: changedFile,
+            line: route.line
+          });
+        }
+      }
+    }
+
+    // Deduplicate routes
+    const uniqueRoutesMap = new Map<string, AffectedRoute>();
+    for (const r of affectedRoutes) {
+      const key = `${r.method}:${r.filePath}:${r.line}`;
+      uniqueRoutesMap.set(key, r);
+    }
+
+    const totalCallersCount = affectedCallers.length;
+    const untestedCallersCount = affectedCallers.filter((c) => !c.hasTest).length;
+
+    return {
+      changedFiles,
+      changedSymbols: changedSymbolsList,
+      affectedFiles: Array.from(affectedFilesSet),
+      affectedCallers,
+      affectedRoutes: Array.from(uniqueRoutesMap.values()),
+      totalCallersCount,
+      untestedCallersCount
+    };
+  }
+
+  private findCallersForSymbol(
+    sym: SymbolInfo,
+    defFile: string,
+    allTestFiles: string[]
+  ): AffectedCaller[] {
+    const callers: AffectedCaller[] = [];
+    const directDependents = this.getDependents(defFile);
+
+    // Also include same file callers
+    const defAnalysis = this.fileAnalyses.get(defFile);
+    if (defAnalysis) {
+      for (const otherSym of defAnalysis.symbols) {
+        if (otherSym.name !== sym.name && otherSym.calls.includes(sym.name)) {
+          const hasTest = this.hasTestCoverage(defFile, otherSym.name, allTestFiles);
+          callers.push({
+            callerName: otherSym.name,
+            filePath: defFile,
+            line: otherSym.startLine,
+            hasTest,
+            testFilePath: hasTest ? this.findMatchingTestFile(defFile, allTestFiles) : undefined
+          });
+        }
+      }
+    }
+
+    for (const depFile of directDependents) {
+      const depAnalysis = this.fileAnalyses.get(depFile);
+      if (!depAnalysis) continue;
+
+      // Check if depFile imports sym
+      const importsSymbol = depAnalysis.imports.some(
+        (imp) =>
+          imp.resolvedPath === defFile &&
+          (imp.specifiers.some((s) => s.name === sym.name || s.propertyName === sym.name) ||
+            imp.specifiers.some((s) => s.isNamespace || s.isDefault))
+      );
+
+      if (!importsSymbol) continue;
+
+      // Check which symbols in depFile call sym.name
+      for (const callerSym of depAnalysis.symbols) {
+        if (
+          callerSym.calls.includes(sym.name) ||
+          callerSym.calls.some((c) => c.endsWith(`.${sym.name}`))
+        ) {
+          const hasTest = this.isTestFile(depFile) || this.hasTestCoverage(depFile, callerSym.name, allTestFiles);
+          callers.push({
+            callerName: callerSym.name,
+            filePath: depFile,
+            line: callerSym.startLine,
+            hasTest,
+            testFilePath: hasTest ? (this.isTestFile(depFile) ? depFile : this.findMatchingTestFile(depFile, allTestFiles)) : undefined
+          });
+        }
+      }
+    }
+
+    return callers;
+  }
+
+  private getTransitiveDependents(file: string, visited = new Set<string>()): Set<string> {
+    if (visited.has(file)) return new Set();
+    visited.add(file);
+
+    const result = new Set<string>();
+    const direct = this.getDependents(file);
+
+    for (const d of direct) {
+      result.add(d);
+      const sub = this.getTransitiveDependents(d, visited);
+      for (const s of sub) {
+        result.add(s);
+      }
+    }
+
+    return result;
+  }
+
+  private hasTestCoverage(sourceFile: string, _symbolName: string, allTestFiles: string[]): boolean {
+    const base = path.basename(sourceFile, path.extname(sourceFile));
+    for (const testFile of allTestFiles) {
+      if (testFile.includes(base)) {
+        return true;
+      }
+      // Check if testFile imports sourceFile
+      const deps = this.fileDependencies.get(testFile);
+      if (deps && deps.has(sourceFile)) {
+        return true;
+      }
+    }
+    return false;
+  }
+
+  private findMatchingTestFile(sourceFile: string, allTestFiles: string[]): string | undefined {
+    const base = path.basename(sourceFile, path.extname(sourceFile));
+    return allTestFiles.find((t) => t.includes(base));
+  }
+}