diff --git a/src/__mocks__/service.mocks.js b/src/__mocks__/service.mocks.js
index 06c69ae..5b735f2 100644
--- a/src/__mocks__/service.mocks.js
+++ b/src/__mocks__/service.mocks.js
@@ -18,6 +18,18 @@ export const mockFsService = {
   getAvailableRoots: vi.fn(),
   pathJoin: vi.fn(),
   isDir: vi.fn(),
+  isFile: vi.fn(),
   readDir: vi.fn(),
   makeDir: vi.fn(),
 };
+
+export const mockShellService = {
+  run: vi.fn(),
+};
+
+export const mockOsService = {
+  isWindows: vi.fn(),
+  isDarwin: vi.fn(),
+  isLinux: vi.fn(),
+  getWorkingDir: vi.fn(),
+};
diff --git a/src/handlers/installationHandlers.js b/src/handlers/installationHandlers.js
index 50cc860..d026c5c 100644
--- a/src/handlers/installationHandlers.js
+++ b/src/handlers/installationHandlers.js
@@ -135,14 +135,6 @@ async function performInstall(config) {
   try {
     if (platform === "win32") {
       try {
-        try {
-          await runCommand("curl --version");
-        } catch (error) {
-          throw new Error(
-            "curl is not available. Please install curl or update your Windows version.",
-          );
-        }
-
         await runCommand(
           "curl -LO --ssl-no-revoke https://get.codex.storage/install.cmd",
         );
diff --git a/src/handlers/installer.js b/src/handlers/installer.js
index 57ba9bd..9fb80a9 100644
--- a/src/handlers/installer.js
+++ b/src/handlers/installer.js
@@ -1,9 +1,130 @@
 export class Installer {
-  constructor(configService) {
+  constructor(configService, shellService, osService, fsService) {
+    this.config = configService.get();
     this.configService = configService;
+    this.shell = shellService;
+    this.os = osService;
+    this.fs = fsService;
   }
 
   isCodexInstalled = async () => {
-    return false;
-  }
-}
\ No newline at end of file
+    try {
+      await this.getCodexVersion();
+      return true;
+    } catch (error) {
+      return false;
+    }
+  };
+
+  getCodexVersion = async () => {
+    if (this.config.codexExe.length < 1)
+      throw new Error("Codex not installed.");
+    const version = await this.shell.run(`"${this.config.codexExe}" --version`);
+    if (version.length < 1) throw new Error("Version info not found.");
+    return version;
+  };
+
+  installCodex = async (processCallbacks) => {
+    if (!(await this.arePrerequisitesCorrect(processCallbacks))) return;
+
+    processCallbacks.installStarts();
+    if (this.os.isWindows()) {
+      await this.installCodexWindows(processCallbacks);
+    } else {
+      await this.installCodexUnix(processCallbacks);
+    }
+
+    if (!(await this.isCodexInstalled()))
+      throw new Error("Codex installation failed.");
+    processCallbacks.installSuccessful();
+  };
+
+  arePrerequisitesCorrect = async (processCallbacks) => {
+    if (await this.isCodexInstalled()) {
+      processCallbacks.warn("Codex is already installed.");
+      return false;
+    }
+    if (this.config.codexInstallPath.length < 1) {
+      processCallbacks.warn("Install path not set.");
+      return false;
+    }
+    if (!(await this.isCurlAvailable())) {
+      processCallbacks.warn("Curl is not available.");
+      return false;
+    }
+    return true;
+  };
+
+  isCurlAvailable = async () => {
+    const curlVersion = await this.shell.run("curl --version");
+    return curlVersion.length > 0;
+  };
+
+  installCodexWindows = async (processCallbacks) => {
+    await this.shell.run(
+      "curl -LO --ssl-no-revoke https://get.codex.storage/install.cmd",
+    );
+    processCallbacks.downloadSuccessful();
+    await this.shell.run(
+      `set "INSTALL_DIR=${this.config.codexInstallPath}" && ` +
+        `"${this.os.getWorkingDir()}\\install.cmd"`,
+    );
+    await this.saveCodexInstallPath("codex.exe");
+    await this.shell.run("del /f install.cmd");
+  };
+
+  installCodexUnix = async (processCallbacks) => {
+    await this.ensureUnixDependencies();
+    await this.shell.run(
+      "curl -# --connect-timeout 10 --max-time 60 -L https://get.codex.storage/install.sh -o install.sh && chmod +x install.sh",
+    );
+    processCallbacks.downloadSuccessful();
+
+    if (this.os.isDarwin()) {
+      await this.runInstallerDarwin();
+    } else {
+      await this.runInstallerLinux();
+    }
+
+    await this.saveCodexInstallPath("codex");
+    await this.shell.run("rm -f install.sh");
+  };
+
+  runInstallerDarwin = async () => {
+    const timeoutCommand = `perl -e '
+    eval {
+        local $SIG{ALRM} = sub { die "timeout\\n" };
+        alarm(120);
+        system("INSTALL_DIR=\\"${this.config.codexInstallPath}\\" bash install.sh");
+        alarm(0);
+    };
+    die if $@;
+'`;
+    await this.shell.run(timeoutCommand);
+  };
+
+  runInstallerLinux = async () => {
+    await this.shell.run(
+      `INSTALL_DIR="${this.config.codexInstallPath}" timeout 120 bash install.sh`,
+    );
+  };
+
+  ensureUnixDependencies = async (processCallbacks) => {
+    const libgompCheck = await this.shell.run("ldconfig -p | grep libgomp");
+    if (libgompCheck.length < 1) {
+      processCallbacks.warn("libgomp not found.");
+      return false;
+    }
+    return true;
+  };
+
+  saveCodexInstallPath = async (codexExe) => {
+    this.config.codexExe = this.fs.pathJoin([
+      this.config.codexInstallPath,
+      codexExe,
+    ]);
+    if (!this.fs.isFile(this.config.codexExe))
+      throw new Error("Codex executable not found.");
+    await this.configService.saveConfig();
+  };
+}
diff --git a/src/handlers/installer.test.js b/src/handlers/installer.test.js
new file mode 100644
index 0000000..4b011d9
--- /dev/null
+++ b/src/handlers/installer.test.js
@@ -0,0 +1,372 @@
+import { describe, beforeEach, it, expect, vi } from "vitest";
+import {
+  mockShellService,
+  mockOsService,
+  mockFsService,
+} from "../__mocks__/service.mocks.js";
+import { mockConfigService } from "../__mocks__/service.mocks.js";
+import { Installer } from "./installer.js";
+
+describe("Installer", () => {
+  const config = {
+    codexInstallPath: "/install-codex",
+  };
+  const workingDir = "/working-dir";
+  const processCallbacks = {
+    installStarts: vi.fn(),
+    downloadSuccessful: vi.fn(),
+    installSuccessful: vi.fn(),
+    warn: vi.fn(),
+  };
+  let installer;
+
+  beforeEach(() => {
+    vi.resetAllMocks();
+    mockConfigService.get.mockReturnValue(config);
+    mockOsService.getWorkingDir.mockReturnValue(workingDir);
+
+    installer = new Installer(
+      mockConfigService,
+      mockShellService,
+      mockOsService,
+      mockFsService,
+    );
+  });
+
+  describe("getCodexVersion", () => {
+    it("throws when codex exe is not set", async () => {
+      config.codexExe = "";
+      await expect(installer.getCodexVersion()).rejects.toThrow(
+        "Codex not installed.",
+      );
+    });
+
+    it("throws when version info is not found", async () => {
+      config.codexExe = "codex.exe";
+      mockShellService.run.mockResolvedValueOnce("");
+      await expect(installer.getCodexVersion()).rejects.toThrow(
+        "Version info not found.",
+      );
+    });
+
+    it("returns version info", async () => {
+      const versionInfo = "versionInfo";
+      config.codexExe = "codex.exe";
+      mockShellService.run.mockResolvedValueOnce(versionInfo);
+      const version = await installer.getCodexVersion();
+      expect(version).toBe(versionInfo);
+    });
+  });
+
+  describe("isCodexInstalled", () => {
+    it("return true when getCodexVersion succeeds", async () => {
+      installer.getCodexVersion = vi.fn();
+      expect(await installer.isCodexInstalled()).toBe(true);
+    });
+
+    it("returns false when getCodexVersion fails", async () => {
+      installer.getCodexVersion = vi.fn(() => {
+        throw new Error("Codex not installed.");
+      });
+      expect(await installer.isCodexInstalled()).toBe(false);
+    });
+  });
+
+  describe("installCodex", () => {
+    beforeEach(() => {
+      installer.arePrerequisitesCorrect = vi.fn();
+      installer.installCodexWindows = vi.fn();
+      installer.installCodexUnix = vi.fn();
+      installer.isCodexInstalled = vi.fn();
+    });
+
+    it("returns early when prerequisites are not correct", async () => {
+      installer.arePrerequisitesCorrect.mockResolvedValue(false);
+      await installer.installCodex(processCallbacks);
+      expect(processCallbacks.installStarts).not.toHaveBeenCalled();
+      expect(processCallbacks.installSuccessful).not.toHaveBeenCalled();
+      expect(processCallbacks.downloadSuccessful).not.toHaveBeenCalled();
+      expect(installer.isCodexInstalled).not.toHaveBeenCalled();
+      expect(installer.installCodexWindows).not.toHaveBeenCalled();
+      expect(installer.installCodexUnix).not.toHaveBeenCalled();
+    });
+
+    describe("prerequisites OK", () => {
+      beforeEach(() => {
+        installer.arePrerequisitesCorrect.mockResolvedValue(true);
+        installer.isCodexInstalled.mockResolvedValue(true);
+      });
+
+      it("calls installStarts when prerequisites are correct", async () => {
+        await installer.installCodex(processCallbacks);
+        expect(processCallbacks.installStarts).toHaveBeenCalled();
+      });
+
+      it("calls installCodexWindows when OS is Windows", async () => {
+        mockOsService.isWindows.mockReturnValue(true);
+        await installer.installCodex(processCallbacks);
+        expect(installer.installCodexWindows).toHaveBeenCalledWith(
+          processCallbacks,
+        );
+      });
+
+      it("calls installCodexUnix when OS is not Windows", async () => {
+        mockOsService.isWindows.mockReturnValue(false);
+        await installer.installCodex(processCallbacks);
+        expect(installer.installCodexUnix).toHaveBeenCalledWith(
+          processCallbacks,
+        );
+      });
+
+      it("throws when codex is not installed after installation", async () => {
+        installer.isCodexInstalled.mockResolvedValue(false);
+        await expect(installer.installCodex(processCallbacks)).rejects.toThrow(
+          "Codex installation failed.",
+        );
+      });
+
+      it("calls installSuccessful when installation is successful", async () => {
+        await installer.installCodex(processCallbacks);
+        expect(processCallbacks.installSuccessful).toHaveBeenCalled();
+      });
+    });
+  });
+
+  describe("arePrerequisitesCorrect", () => {
+    beforeEach(() => {
+      installer.isCodexInstalled = vi.fn();
+      installer.isCurlAvailable = vi.fn();
+      config.codexInstallPath = "/install-codex";
+    });
+
+    it("returns false when codex is already installed", async () => {
+      installer.isCodexInstalled.mockResolvedValue(true);
+      expect(await installer.arePrerequisitesCorrect(processCallbacks)).toBe(
+        false,
+      );
+      expect(processCallbacks.warn).toHaveBeenCalledWith(
+        "Codex is already installed.",
+      );
+    });
+
+    it("returns false when install path is not set", async () => {
+      config.codexInstallPath = "";
+      expect(await installer.arePrerequisitesCorrect(processCallbacks)).toBe(
+        false,
+      );
+      expect(processCallbacks.warn).toHaveBeenCalledWith(
+        "Install path not set.",
+      );
+    });
+
+    it("returns false when curl is not available", async () => {
+      installer.isCodexInstalled.mockResolvedValue(false);
+      installer.isCurlAvailable.mockResolvedValue(false);
+      expect(await installer.arePrerequisitesCorrect(processCallbacks)).toBe(
+        false,
+      );
+      expect(processCallbacks.warn).toHaveBeenCalledWith(
+        "Curl is not available.",
+      );
+    });
+
+    it("returns true when all prerequisites are correct", async () => {
+      installer.isCodexInstalled.mockResolvedValue(false);
+      installer.isCurlAvailable.mockResolvedValue(true);
+      const result = await installer.arePrerequisitesCorrect(processCallbacks);
+      expect(result).toBe(true);
+    });
+  });
+
+  describe("isCurlAvailable", () => {
+    it("returns true when curl version is found", async () => {
+      mockShellService.run.mockResolvedValueOnce("curl version");
+      const result = await installer.isCurlAvailable();
+      expect(mockShellService.run).toHaveBeenCalledWith("curl --version");
+      expect(result).toBe(true);
+    });
+
+    it("returns false when curl version is not found", async () => {
+      mockShellService.run.mockResolvedValueOnce("");
+      const result = await installer.isCurlAvailable();
+      expect(mockShellService.run).toHaveBeenCalledWith("curl --version");
+      expect(result).toBe(false);
+    });
+  });
+
+  describe("install functions", () => {
+    beforeEach(() => {
+      installer.saveCodexInstallPath = vi.fn();
+    });
+
+    describe("installCodexWindows", () => {
+      it("runs the curl command to download the installer", async () => {
+        await installer.installCodexWindows(processCallbacks);
+        expect(mockShellService.run).toHaveBeenCalledWith(
+          "curl -LO --ssl-no-revoke https://get.codex.storage/install.cmd",
+        );
+      });
+
+      it("calls downloadSuccessful", async () => {
+        await installer.installCodexWindows(processCallbacks);
+        expect(processCallbacks.downloadSuccessful).toHaveBeenCalled();
+      });
+
+      it("runs installer script", async () => {
+        await installer.installCodexWindows(processCallbacks);
+        expect(mockShellService.run).toHaveBeenCalledWith(
+          `set "INSTALL_DIR=${config.codexInstallPath}" && "${workingDir}\\install.cmd"`,
+        );
+      });
+
+      it("saves the codex install path", async () => {
+        await installer.installCodexWindows(processCallbacks);
+        expect(installer.saveCodexInstallPath).toHaveBeenCalledWith(
+          "codex.exe",
+        );
+      });
+
+      it("deletes the installer script", async () => {
+        await installer.installCodexWindows(processCallbacks);
+        expect(mockShellService.run).toHaveBeenCalledWith("del /f install.cmd");
+      });
+    });
+
+    describe("installCodexUnix", () => {
+      beforeEach(() => {
+        installer.ensureUnixDependencies = vi.fn();
+        installer.runInstallerDarwin = vi.fn();
+        installer.runInstallerLinux = vi.fn();
+      });
+
+      it("ensures Unix dependencies", async () => {
+        await installer.installCodexUnix(processCallbacks);
+        expect(installer.ensureUnixDependencies).toHaveBeenCalled();
+      });
+
+      it("runs the curl command to download the installer", async () => {
+        await installer.installCodexUnix(processCallbacks);
+        expect(mockShellService.run).toHaveBeenCalledWith(
+          "curl -# --connect-timeout 10 --max-time 60 -L https://get.codex.storage/install.sh -o install.sh && chmod +x install.sh",
+        );
+      });
+
+      it("calls downloadSuccessful", async () => {
+        await installer.installCodexUnix(processCallbacks);
+        expect(processCallbacks.downloadSuccessful).toHaveBeenCalled();
+      });
+
+      it("runs installer for darwin ", async () => {
+        mockOsService.isDarwin.mockReturnValue(true);
+        await installer.installCodexUnix(processCallbacks);
+        expect(installer.runInstallerDarwin).toHaveBeenCalled();
+      });
+
+      it("runs installer for linux", async () => {
+        mockOsService.isDarwin.mockReturnValue(false);
+        await installer.installCodexUnix(processCallbacks);
+        expect(installer.runInstallerLinux).toHaveBeenCalled();
+      });
+
+      it("saves the codex install path", async () => {
+        await installer.installCodexUnix(processCallbacks);
+        expect(installer.saveCodexInstallPath).toHaveBeenCalledWith("codex");
+      });
+
+      it("deletes the installer script", async () => {
+        await installer.installCodexUnix(processCallbacks);
+        expect(mockShellService.run).toHaveBeenCalledWith("rm -f install.sh");
+      });
+    });
+
+    describe("runInstallerDarwin", () => {
+      it("runs the installer script for darwin with custom timeout command", async () => {
+        const timeoutCommand = `perl -e '
+    eval {
+        local $SIG{ALRM} = sub { die "timeout\\n" };
+        alarm(120);
+        system("INSTALL_DIR=\\"${config.codexInstallPath}\\" bash install.sh");
+        alarm(0);
+    };
+    die if $@;
+'`;
+        await installer.runInstallerDarwin();
+        expect(mockShellService.run).toHaveBeenCalledWith(timeoutCommand);
+      });
+    });
+
+    describe("runInstallerLinux", () => {
+      it("runs the installer script using unix timeout command", async () => {
+        await installer.runInstallerLinux();
+        expect(mockShellService.run).toHaveBeenCalledWith(
+          `INSTALL_DIR="${config.codexInstallPath}" timeout 120 bash install.sh`,
+        );
+      });
+    });
+  });
+
+  describe("ensureUnixDependencies", () => {
+    it("returns true when libgomp is installed", async () => {
+      mockShellService.run.mockResolvedValueOnce("yes");
+      expect(await installer.ensureUnixDependencies(processCallbacks)).toBe(
+        true,
+      );
+      expect(mockShellService.run).toHaveBeenCalledWith(
+        "ldconfig -p | grep libgomp",
+      );
+    });
+
+    it("returns false when libgomp is not found", async () => {
+      mockShellService.run.mockResolvedValue("");
+      expect(await installer.ensureUnixDependencies(processCallbacks)).toBe(
+        false,
+      );
+      expect(mockShellService.run).toHaveBeenCalledWith(
+        "ldconfig -p | grep libgomp",
+      );
+    });
+
+    it("it calls warn in processCallbacks when libgomp is not found", async () => {
+      mockShellService.run.mockResolvedValue("");
+      await installer.ensureUnixDependencies(processCallbacks);
+      expect(processCallbacks.warn).toHaveBeenCalledWith("libgomp not found.");
+    });
+  });
+
+  describe("saveCodexInstallPath", () => {
+    const codexExe = "_codex_.exe";
+    const pathJointResult = "/path-to-codex/_codex_.exe";
+
+    beforeEach(() => {
+      mockFsService.pathJoin.mockReturnValue(pathJointResult);
+    });
+
+    it("combines the install path with the exe", async () => {
+      mockFsService.isFile.mockReturnValue(true);
+      await installer.saveCodexInstallPath(codexExe);
+      expect(mockFsService.pathJoin).toHaveBeenCalledWith([
+        config.codexInstallPath,
+        codexExe,
+      ]);
+    });
+
+    it("sets the codex exe path", async () => {
+      mockFsService.isFile.mockReturnValue(true);
+      await installer.saveCodexInstallPath(codexExe);
+      expect(config.codexExe).toBe(pathJointResult);
+    });
+
+    it("throws when file does not exist", async () => {
+      mockFsService.isFile.mockReturnValue(false);
+      await expect(installer.saveCodexInstallPath(codexExe)).rejects.toThrow(
+        "Codex executable not found.",
+      );
+    });
+
+    it("saves the config", async () => {
+      mockFsService.isFile.mockReturnValue(true);
+      await installer.saveCodexInstallPath(codexExe);
+      expect(mockConfigService.saveConfig).toHaveBeenCalled();
+    });
+  });
+});
diff --git a/src/main.js b/src/main.js
index 4cd4c53..060fa86 100644
--- a/src/main.js
+++ b/src/main.js
@@ -112,7 +112,7 @@ export async function main() {
     new MenuLoop(),
     installMenu,
     configMenu,
-    new DataDirMover(fsService, uiService)
+    new DataDirMover(fsService, uiService),
   );
 
   await mainMenu.show();
diff --git a/src/services/fsService.js b/src/services/fsService.js
index 645a099..8590652 100644
--- a/src/services/fsService.js
+++ b/src/services/fsService.js
@@ -31,6 +31,14 @@ export class FsService {
     }
   };
 
+  isFile = (path) => {
+    try {
+      return fs.lstatSync(path).isFile();
+    } catch {
+      return false;
+    }
+  };
+
   readDir = (dir) => {
     return fs.readdirSync(dir);
   };
diff --git a/src/services/osService.js b/src/services/osService.js
new file mode 100644
index 0000000..3ec8f05
--- /dev/null
+++ b/src/services/osService.js
@@ -0,0 +1,23 @@
+import os from "os";
+
+export class OsService {
+  constructor() {
+    this.platform = os.platform();
+  }
+
+  isWindows = () => {
+    return this.platform === "win32";
+  };
+
+  isDarwin = () => {
+    return this.platform === "darwin";
+  };
+
+  isLinux = () => {
+    return this.platform === "linux";
+  };
+
+  getWorkingDir = () => {
+    return process.cwd();
+  };
+}
diff --git a/src/services/shellService.js b/src/services/shellService.js
new file mode 100644
index 0000000..df9f63e
--- /dev/null
+++ b/src/services/shellService.js
@@ -0,0 +1,18 @@
+import { exec } from "child_process";
+import { promisify } from "util";
+
+export class ShellService {
+  constructor() {
+    this.execAsync = promisify(exec);
+  }
+
+  async run(command) {
+    try {
+      const { stdout, stderr } = await this.execAsync(command);
+      return stdout;
+    } catch (error) {
+      console.error("Error:", error.message);
+      throw error;
+    }
+  }
+}
diff --git a/src/ui/installMenu.js b/src/ui/installMenu.js
index b42eb82..4c4b50d 100644
--- a/src/ui/installMenu.js
+++ b/src/ui/installMenu.js
@@ -9,7 +9,7 @@ export class InstallMenu {
   show = async () => {
     await this.ui.askMultipleChoice("Configure your Codex installation", [
       {
-        label: "Install path: " + this.config.codexPath,
+        label: "Install path: " + this.config.codexInstallPath,
         action: this.selectInstallPath,
       },
       {
@@ -28,8 +28,8 @@ export class InstallMenu {
   };
 
   selectInstallPath = async () => {
-    this.config.codexPath = await this.pathSelector.show(
-      this.config.codexPath,
+    this.config.codexInstallPath = await this.pathSelector.show(
+      this.config.codexInstallPath,
       false,
     );
     this.configService.saveConfig();
diff --git a/src/ui/installMenu.test.js b/src/ui/installMenu.test.js
index 1a0c7c9..2e15e89 100644
--- a/src/ui/installMenu.test.js
+++ b/src/ui/installMenu.test.js
@@ -6,7 +6,7 @@ import { mockPathSelector } from "../__mocks__/utils.mocks.js";
 
 describe("InstallMenu", () => {
   const config = {
-    codexPath: "/codex",
+    codexInstallPath: "/codex",
   };
   let installMenu;
 
@@ -27,7 +27,7 @@ describe("InstallMenu", () => {
       "Configure your Codex installation",
       [
         {
-          label: "Install path: " + config.codexPath,
+          label: "Install path: " + config.codexInstallPath,
           action: installMenu.selectInstallPath,
         },
         {
@@ -47,14 +47,14 @@ describe("InstallMenu", () => {
   });
 
   it("allows selecting the install path", async () => {
-    const originalPath = config.codexPath;
+    const originalPath = config.codexInstallPath;
     const newPath = "/new/path";
     mockPathSelector.show.mockResolvedValue(newPath);
 
     await installMenu.selectInstallPath();
 
     expect(mockPathSelector.show).toHaveBeenCalledWith(originalPath, false);
-    expect(config.codexPath).toBe(newPath);
+    expect(config.codexInstallPath).toBe(newPath);
     expect(mockConfigService.saveConfig).toHaveBeenCalled();
   });
 
diff --git a/src/utils/command.js b/src/utils/command.js
deleted file mode 100644
index 9ef5c91..0000000
--- a/src/utils/command.js
+++ /dev/null
@@ -1,14 +0,0 @@
-import { exec } from "child_process";
-import { promisify } from "util";
-
-export const execAsync = promisify(exec);
-
-export async function runCommand(command) {
-  try {
-    const { stdout, stderr } = await execAsync(command);
-    return stdout;
-  } catch (error) {
-    console.error("Error:", error.message);
-    throw error;
-  }
-}