diff --git a/index.ts b/index.ts
index 4baf40f9..90e65748 100644
--- a/index.ts
+++ b/index.ts
@@ -416,6 +416,8 @@ function toImportSpecifier(value: string): string {
   if (!trimmed) return "";
   if (trimmed.startsWith("file://")) return trimmed;
   if (trimmed.startsWith("/")) return pathToFileURL(trimmed).href;
+  // Handle Windows absolute paths (e.g. C:\Users\... or D:/Program Files/...)
+  if (/^[a-zA-Z]:[/\\]/.test(trimmed)) return pathToFileURL(trimmed).href;
   return trimmed;
 }
 function getExtensionApiImportSpecifiers(): string[] {
@@ -435,6 +437,11 @@ function getExtensionApiImportSpecifiers(): string[] {
   specifiers.push(toImportSpecifier("/usr/local/lib/node_modules/openclaw/dist/extensionAPI.js"));
   specifiers.push(toImportSpecifier("/opt/homebrew/lib/node_modules/openclaw/dist/extensionAPI.js"));
 
+  if (process.platform === "win32" && process.env.APPDATA) {
+    const windowsNpmPath = join(process.env.APPDATA, "npm", "node_modules", "openclaw", "dist", "extensionAPI.js");
+    specifiers.push(toImportSpecifier(windowsNpmPath));
+  }
+
   return [...new Set(specifiers.filter(Boolean))];
 }
 
diff --git a/test/to-import-specifier-windows.test.mjs b/test/to-import-specifier-windows.test.mjs
new file mode 100644
index 00000000..70772308
--- /dev/null
+++ b/test/to-import-specifier-windows.test.mjs
@@ -0,0 +1,260 @@
+/**
+ * Test: toImportSpecifier and Windows path fallback
+ * PR #576 - Windows APPDATA path fallback for extensionAPI.js
+ *
+ * Tests the behavior of `toImportSpecifier` and `getExtensionApiImportSpecifiers`
+ * using local implementations that mirror the PR #576 code exactly.
+ * Functions are NOT exported from index.ts, so we copy the logic to test it.
+ */
+import { describe, it } from "node:test";
+import assert from "node:assert/strict";
+import { join } from "node:path";
+import { pathToFileURL } from "node:url";
+
+// Copy of the PR #576 toImportSpecifier implementation (index.ts:414-423)
+function toImportSpecifier(value) {
+  const trimmed = value.trim();
+  if (!trimmed) return "";
+  if (trimmed.startsWith("file://")) return trimmed;
+  if (trimmed.startsWith("/")) return pathToFileURL(trimmed).href;
+  // Handle Windows absolute paths (e.g. C:\Users\... or D:/Program Files/...)
+  if (/^[a-zA-Z]:[/\\]/.test(trimmed)) return pathToFileURL(trimmed).href;
+  return trimmed;
+}
+
+// Copy of the PR #576 getExtensionApiImportSpecifiers implementation (index.ts:425-444)
+// Note: intentionally does NOT include the requireFromHere.resolve() call (dead code)
+function getExtensionApiImportSpecifiers() {
+  const envPath = process.env.OPENCLAW_EXTENSION_API_PATH?.trim();
+  const specifiers = [];
+
+  if (envPath) specifiers.push(toImportSpecifier(envPath));
+  specifiers.push("openclaw/dist/extensionAPI.js");
+
+  specifiers.push(toImportSpecifier("/usr/lib/node_modules/openclaw/dist/extensionAPI.js"));
+  specifiers.push(toImportSpecifier("/usr/local/lib/node_modules/openclaw/dist/extensionAPI.js"));
+  specifiers.push(toImportSpecifier("/opt/homebrew/lib/node_modules/openclaw/dist/extensionAPI.js"));
+
+  if (process.platform === "win32" && process.env.APPDATA) {
+    const windowsNpmPath = join(process.env.APPDATA, "npm", "node_modules", "openclaw", "dist", "extensionAPI.js");
+    specifiers.push(toImportSpecifier(windowsNpmPath));
+  }
+
+  return [...new Set(specifiers.filter(Boolean))];
+}
+
+// Env helper: set key to value, run fn, restore original
+function withEnv(key, value, fn) {
+  const original = process.env[key];
+  if (value === undefined) {
+    delete process.env[key];
+  } else {
+    process.env[key] = value;
+  }
+  try {
+    fn();
+  } finally {
+    if (original === undefined) {
+      delete process.env[key];
+    } else {
+      process.env[key] = original;
+    }
+  }
+}
+
+// ============================================================================
+// toImportSpecifier tests
+// ============================================================================
+
+describe("toImportSpecifier", () => {
+  // --- POSIX paths ---
+  it("converts POSIX absolute path to file:// URL", () => {
+    const result = toImportSpecifier("/usr/local/lib/node_modules/openclaw/dist/extensionAPI.js");
+    assert.ok(result.startsWith("file://"), `Expected file:// URL, got: ${result}`);
+    assert.ok(result.includes("/usr/local/lib"));
+  });
+
+  it("converts POSIX path with spaces to file:// URL", () => {
+    const result = toImportSpecifier("/opt/My App/node_modules/test.js");
+    assert.ok(result.startsWith("file://"), `Expected file:// URL, got: ${result}`);
+  });
+
+  // --- Windows paths (PR #576 new fix) ---
+  it("converts Windows drive-letter backslash path to file:// URL", () => {
+    const result = toImportSpecifier("C:\\Users\\admin\\AppData\\Roaming\\npm\\node_modules\\openclaw\\dist\\extensionAPI.js");
+    assert.ok(result.startsWith("file://"), `Expected file:// URL, got: ${result}`);
+    assert.ok(result.includes("C:/"), `Expected C:/ prefix, got: ${result}`);
+  });
+
+  it("converts Windows drive-letter forward-slash path to file:// URL", () => {
+    const result = toImportSpecifier("D:/Program Files/openclaw/dist/extensionAPI.js");
+    assert.ok(result.startsWith("file://"), `Expected file:// URL, got: ${result}`);
+    assert.ok(result.includes("D:/"), `Expected D:/ prefix, got: ${result}`);
+  });
+
+  it("converts Windows path with spaces to file:// URL", () => {
+    const result = toImportSpecifier("E:\\code\\my project\\file.js");
+    assert.ok(result.startsWith("file://"), `Expected file:// URL, got: ${result}`);
+  });
+
+  it("rejects Windows drive letter without separator (C: -> unchanged)", () => {
+    const result = toImportSpecifier("C:");
+    assert.equal(result, "C:");
+  });
+
+  it("rejects DOS 8.3 short path (C:path\\to\\file.js -> unchanged)", () => {
+    const result = toImportSpecifier("C:path\\to\\file.js");
+    assert.equal(result, "C:path\\to\\file.js");
+  });
+
+  it("rejects single-backslash UNC-like path (\\server\\share -> unchanged)", () => {
+    const result = toImportSpecifier("\\server\\share\\file.js");
+    assert.equal(result, "\\server\\share\\file.js");
+  });
+
+  // --- Pass-through cases ---
+  it("passes through file:// POSIX URL unchanged", () => {
+    const input = "file:///usr/local/lib/extensionAPI.js";
+    const result = toImportSpecifier(input);
+    assert.equal(result, input);
+  });
+
+  it("passes through file:// Windows path unchanged", () => {
+    const input = "file:///C:/Users/admin/AppData/Roaming/test.js";
+    const result = toImportSpecifier(input);
+    assert.equal(result, input);
+  });
+
+  it("passes through bare module specifier unchanged", () => {
+    const input = "openclaw/dist/extensionAPI.js";
+    const result = toImportSpecifier(input);
+    assert.equal(result, input);
+  });
+
+  it("passes through relative path unchanged", () => {
+    const input = "./lib/extensionAPI.js";
+    const result = toImportSpecifier(input);
+    assert.equal(result, input);
+  });
+
+  // --- Edge cases ---
+  it("returns empty string for whitespace-only input", () => {
+    const result = toImportSpecifier("   ");
+    assert.equal(result, "");
+  });
+
+  it("handles path with trailing slash", () => {
+    const result = toImportSpecifier("C:\\Users\\admin\\");
+    assert.ok(result.startsWith("file://"), `Expected file:// URL, got: ${result}`);
+  });
+
+  it("handles lowercase drive letter", () => {
+    const result = toImportSpecifier("c:\\users\\test\\file.js");
+    assert.ok(result.startsWith("file://"), `Expected file:// URL, got: ${result}`);
+  });
+
+  it("handles uppercase drive letter", () => {
+    const result = toImportSpecifier("E:\\Users\\Admin\\Desktop\\file.js");
+    assert.ok(result.startsWith("file://"), `Expected file:// URL, got: ${result}`);
+  });
+});
+
+// ============================================================================
+// getExtensionApiImportSpecifiers tests
+// ============================================================================
+
+describe("getExtensionApiImportSpecifiers", () => {
+  it("always includes bare module specifier", () => {
+    const specifiers = getExtensionApiImportSpecifiers();
+    assert.ok(specifiers.includes("openclaw/dist/extensionAPI.js"), "Should include bare module specifier");
+  });
+
+  it("includes OPENCLAW_EXTENSION_API_PATH POSIX path as file:// URL", () => {
+    withEnv("OPENCLAW_EXTENSION_API_PATH", "/custom/path/extensionAPI.js", () => {
+      const specifiers = getExtensionApiImportSpecifiers();
+      const found = specifiers.find(s => s.includes("/custom/path"));
+      assert.ok(found, `Expected custom path, got: ${JSON.stringify(specifiers)}`);
+      assert.ok(found.startsWith("file://"), `Expected file:// URL, got: ${found}`);
+    });
+  });
+
+  it("converts OPENCLAW_EXTENSION_API_PATH Windows path to file:// URL (hidden issue #1 fix)", () => {
+    withEnv("OPENCLAW_EXTENSION_API_PATH", "C:\\Program Files\\openclaw\\dist\\extensionAPI.js", () => {
+      const specifiers = getExtensionApiImportSpecifiers();
+      const winSpec = specifiers.find(s => s.startsWith("file:///C:/") && s.includes("openclaw") && s.includes("dist") && s.includes("extensionAPI"));
+      assert.ok(winSpec, `Expected Windows path as file:// URL: ${JSON.stringify(specifiers)}`);
+      assert.ok(winSpec.includes("Program") || winSpec.includes("Program%20"), `Expected Program Files in path, got: ${winSpec}`);
+    });
+  });
+
+  it("includes POSIX fallback paths on all platforms", () => {
+    const specifiers = getExtensionApiImportSpecifiers();
+    assert.ok(specifiers.some(s => s.includes("/usr/lib")), `Expected /usr/lib path, got: ${JSON.stringify(specifiers)}`);
+    assert.ok(specifiers.some(s => s.includes("/usr/local")), `Expected /usr/local path, got: ${JSON.stringify(specifiers)}`);
+    assert.ok(specifiers.some(s => s.includes("/opt/homebrew")), `Expected /opt/homebrew path, got: ${JSON.stringify(specifiers)}`);
+  });
+
+  it("returns deduped specifiers (no duplicates)", () => {
+    const specifiers = getExtensionApiImportSpecifiers();
+    const unique = [...new Set(specifiers)];
+    assert.equal(specifiers.length, unique.length, `Found duplicate specifiers: ${JSON.stringify(specifiers)}`);
+  });
+
+  it("does not include empty strings", () => {
+    const specifiers = getExtensionApiImportSpecifiers();
+    assert.ok(!specifiers.includes(""), "Should not contain empty strings");
+    assert.ok(!specifiers.some(s => typeof s === "string" && s.trim() === ""), "Should not contain whitespace-only strings");
+  });
+
+  it("on non-win32, does NOT add APPDATA fallback", () => {
+    if (process.platform !== "win32") {
+      const specifiers = getExtensionApiImportSpecifiers();
+      const hasAppData = specifiers.some(s => s.includes("AppData") && s.includes("npm"));
+      assert.ok(!hasAppData, "Non-Windows should not add APPDATA fallback");
+    }
+  });
+
+  it("on win32 with APPDATA, includes APPDATA fallback as file:// URL", () => {
+    if (process.platform === "win32" && process.env.APPDATA) {
+      const specifiers = getExtensionApiImportSpecifiers();
+      const appDataSpec = specifiers.find(s => s.includes("AppData") && s.includes("npm"));
+      assert.ok(appDataSpec, `Expected APPDATA path in specifiers: ${JSON.stringify(specifiers)}`);
+      assert.ok(appDataSpec.startsWith("file://"), `APPDATA specifier should be file:// URL, got: ${appDataSpec}`);
+    }
+  });
+
+  it("on win32 without APPDATA env var, does not crash", () => {
+    if (process.platform === "win32") {
+      const original = process.env.APPDATA;
+      delete process.env.APPDATA;
+      try {
+        // Should not throw - just skip the APPDATA fallback
+        const specifiers = getExtensionApiImportSpecifiers();
+        assert.ok(Array.isArray(specifiers), "Should return array even without APPDATA");
+      } finally {
+        if (original !== undefined) process.env.APPDATA = original;
+      }
+    }
+  });
+});
+
+// ============================================================================
+// Integration: pathToFileURL Windows path conversion
+// ============================================================================
+
+describe("pathToFileURL Windows path conversion", () => {
+  it("produces valid file:// URL from Windows backslash path", async () => {
+    const { pathToFileURL } = await import("node:url");
+    const input = "C:\\Users\\admin\\AppData\\Roaming\\npm\\node_modules\\openclaw\\dist\\extensionAPI.js";
+    const result = pathToFileURL(input).href;
+    assert.equal(result, "file:///C:/Users/admin/AppData/Roaming/npm/node_modules/openclaw/dist/extensionAPI.js");
+  });
+
+  it("produces valid file:// URL from Windows forward-slash path", async () => {
+    const { pathToFileURL } = await import("node:url");
+    const input = "D:/Program Files/openclaw/dist/extensionAPI.js";
+    const result = pathToFileURL(input).href;
+    assert.ok(result.startsWith("file://"));
+    assert.ok(result.includes("D:/"));
+  });
+});
\ No newline at end of file