diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5f871aff..e0eaada1 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,7 @@
 ### Added
 
 - App visibility: `base44 visibility <public|private|workspace>` sets it on the server directly (accepts `--app-id` to target any app). Also configurable via `"visibility"` in `config.jsonc`, which `base44 deploy` applies. New projects scaffold `"visibility": "public"`.
+- `base44 build` runs the site's `buildCommand` with `VITE_BASE44_APP_ID` injected, so built bundles always carry the linked app's id.
 
 ### Fixed
 
diff --git a/packages/cli/src/cli/commands/project/build.ts b/packages/cli/src/cli/commands/project/build.ts
new file mode 100644
index 00000000..747329ce
--- /dev/null
+++ b/packages/cli/src/cli/commands/project/build.ts
@@ -0,0 +1,32 @@
+import type { Command } from "commander";
+import { runSiteBuild } from "@/cli/commands/project/site-build.js";
+import type { CLIContext, RunCommandResult } from "@/cli/types.js";
+import { Base44Command, theme } from "@/cli/utils/index.js";
+import { ConfigInvalidError } from "@/core/errors.js";
+import { readProjectConfig } from "@/core/project/index.js";
+
+async function buildAction(ctx: CLIContext): Promise<RunCommandResult> {
+  const { app } = ctx;
+  if (!app?.projectRoot) {
+    throw new ConfigInvalidError(
+      "base44 build requires a linked local project. Run it from a project with base44/.app.jsonc.",
+    );
+  }
+
+  const { project } = await readProjectConfig(app.projectRoot);
+  await runSiteBuild(ctx, {
+    root: project.root,
+    buildCommand: project.site?.buildCommand,
+    appId: app.id,
+  });
+
+  return {
+    outroMessage: `Site built with app id ${theme.styles.bold(app.id)}`,
+  };
+}
+
+export function getBuildCommand(): Command {
+  return new Base44Command("build")
+    .description("Build the site with the Base44 app id injected")
+    .action(buildAction);
+}
diff --git a/packages/cli/src/cli/commands/project/site-build.ts b/packages/cli/src/cli/commands/project/site-build.ts
new file mode 100644
index 00000000..9a51a6cc
--- /dev/null
+++ b/packages/cli/src/cli/commands/project/site-build.ts
@@ -0,0 +1,39 @@
+import { execa } from "execa";
+import type { CLIContext } from "@/cli/types.js";
+import { ConfigNotFoundError } from "@/core/errors.js";
+
+interface SiteBuildTarget {
+  root: string;
+  buildCommand?: string;
+  appId: string;
+}
+
+export async function runSiteBuild(
+  { runTask }: Pick<CLIContext, "runTask">,
+  { root, buildCommand, appId }: SiteBuildTarget,
+): Promise<void> {
+  if (!buildCommand) {
+    throw new ConfigNotFoundError("No site build command found.", {
+      hints: [
+        {
+          message:
+            'Add \'site.buildCommand\' to your config.jsonc (e.g., "site": { "buildCommand": "npm run build" })',
+        },
+      ],
+    });
+  }
+
+  await runTask(
+    "Building site...",
+    () =>
+      execa({
+        cwd: root,
+        shell: true,
+        env: { VITE_BASE44_APP_ID: appId },
+      })`${buildCommand}`,
+    {
+      successMessage: "Site built successfully",
+      errorMessage: "Build failed",
+    },
+  );
+}
diff --git a/packages/cli/src/cli/program.ts b/packages/cli/src/cli/program.ts
index b3a7a87f..04e1c33e 100644
--- a/packages/cli/src/cli/program.ts
+++ b/packages/cli/src/cli/program.ts
@@ -9,6 +9,7 @@ import { getConnectorsCommand } from "@/cli/commands/connectors/index.js";
 import { getDashboardCommand } from "@/cli/commands/dashboard/index.js";
 import { getEntitiesPushCommand } from "@/cli/commands/entities/push.js";
 import { getFunctionsCommand } from "@/cli/commands/functions/index.js";
+import { getBuildCommand } from "@/cli/commands/project/build.js";
 import { getCreateCommand } from "@/cli/commands/project/create.js";
 import { getDeployCommand } from "@/cli/commands/project/deploy.js";
 import { getLinkCommand } from "@/cli/commands/project/link.js";
@@ -69,6 +70,7 @@ export function createProgram(context: CLIContext): Command {
   program.addCommand(getCreateCommand());
   program.addCommand(getScaffoldCommand());
   program.addCommand(getDashboardCommand());
+  program.addCommand(getBuildCommand());
   program.addCommand(getDeployCommand());
   program.addCommand(getVisibilityCommand());
   program.addCommand(getLinkCommand());
diff --git a/packages/cli/tests/cli/build.spec.ts b/packages/cli/tests/cli/build.spec.ts
new file mode 100644
index 00000000..d8d390db
--- /dev/null
+++ b/packages/cli/tests/cli/build.spec.ts
@@ -0,0 +1,43 @@
+import { describe, expect, it } from "vitest";
+import { fixture, setupCLITests } from "./testkit/index.js";
+
+describe("build command", () => {
+  const t = setupCLITests();
+
+  it("runs the site buildCommand with the app id injected", async () => {
+    await t.givenLoggedInWithProject(fixture("with-buildable-site"));
+
+    const result = await t.run("build");
+
+    t.expectResult(result).toSucceed();
+    expect(await t.readProjectFile("build-env.txt")).toBe(
+      `BUILD_APP=${t.api.appId}`,
+    );
+  });
+
+  it("fails when the project has no site.buildCommand", async () => {
+    await t.givenLoggedInWithProject(fixture("with-site"));
+
+    const result = await t.run("build");
+
+    t.expectResult(result).toFail();
+    t.expectResult(result).toContain("No site build command found");
+  });
+
+  it("fails when the buildCommand fails", async () => {
+    await t.givenLoggedInWithProject(fixture("with-failing-build"));
+
+    const result = await t.run("build");
+
+    t.expectResult(result).toFail();
+    t.expectResult(result).toContain("Build failed");
+  });
+
+  it("fails when not in a project directory", async () => {
+    await t.givenLoggedIn({ email: "test@example.com", name: "Test User" });
+
+    const result = await t.run("build");
+
+    t.expectResult(result).toFail();
+  });
+});
diff --git a/packages/cli/tests/fixtures/with-buildable-site/base44/config.jsonc b/packages/cli/tests/fixtures/with-buildable-site/base44/config.jsonc
new file mode 100644
index 00000000..05abc950
--- /dev/null
+++ b/packages/cli/tests/fixtures/with-buildable-site/base44/config.jsonc
@@ -0,0 +1,6 @@
+{
+  "name": "Buildable Site Project",
+  "site": {
+    "buildCommand": "node -e \"require('fs').writeFileSync('build-env.txt', 'BUILD_APP=' + process.env.VITE_BASE44_APP_ID)\""
+  }
+}
diff --git a/packages/cli/tests/fixtures/with-failing-build/base44/config.jsonc b/packages/cli/tests/fixtures/with-failing-build/base44/config.jsonc
new file mode 100644
index 00000000..fb3844ea
--- /dev/null
+++ b/packages/cli/tests/fixtures/with-failing-build/base44/config.jsonc
@@ -0,0 +1,6 @@
+{
+  "name": "Failing Build Project",
+  "site": {
+    "buildCommand": "node -e \"process.exit(1)\""
+  }
+}