diff --git a/.env.example b/.env.example
index 3205c40..b6c0ae7 100644
--- a/.env.example
+++ b/.env.example
@@ -3,7 +3,14 @@ DATABASE_URL=postgres://openbot:openbot@localhost:5432/openbot
 # development. Production refuses to start with this key.
 #   openssl rand -base64 32
 KEY_ENCRYPTION_KEY=AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=
-PORT=3001
+# Where the API listens. SERVER_PORT is the name start.sh, Vite, and the ports table already use.
+# PORT is the older alias; the process still honours it when SERVER_PORT is unset, so an existing
+# .env that only sets PORT keeps working.
+SERVER_PORT=3001
+# PORT=3001
+#
+# Where the app is served. start.sh and Vite both read this; the default is 3010.
+# APP_PORT=3010
 TENANT_PACKAGE_DIR=../examples/fintech
 # What this deployment calls itself, when more than one shares an Intelligence project. A copy of a
 # deployment made for development uses the same project key, and threads are listed per Bot with
diff --git a/app/vite.config.ts b/app/vite.config.ts
index 9ec5e21..31fa717 100644
--- a/app/vite.config.ts
+++ b/app/vite.config.ts
@@ -4,6 +4,9 @@ import { tanstackRouter } from "@tanstack/router-plugin/vite";
 import react from "@vitejs/plugin-react";
 import { defineConfig } from "vite";
 
+const apiPort =
+  process.env.SERVER_PORT?.trim() || process.env.PORT?.trim() || "3001";
+
 export default defineConfig({
   plugins: [tanstackRouter(), react(), tailwindcss()],
   resolve: {
@@ -18,7 +21,7 @@ export default defineConfig({
       // `ws: true` is required for the live screen. Without it Vite answers the upgrade request with
       // the app's HTML and the socket fails with an opaque error that looks like a server problem.
       "/api": {
-        target: `http://localhost:${process.env.SERVER_PORT ?? "3001"}`,
+        target: `http://localhost:${apiPort}`,
         ws: true,
       },
     },
diff --git a/docs/configuration.md b/docs/configuration.md
index 0657fb2..791da46 100644
--- a/docs/configuration.md
+++ b/docs/configuration.md
@@ -32,7 +32,7 @@ All four Intelligence values are required together. Missing any of them stops se
 
 | Variable             | Default                            | Meaning                                                             |
 | -------------------- | ---------------------------------- | ------------------------------------------------------------------- |
-| `PORT`               | `3001`                             | API server port.                                                    |
+| `SERVER_PORT`        | `3001`                             | API server port. `PORT` is the same setting when `SERVER_PORT` is unset. |
 | `NODE_ENV`           | unset                              | `production` enables startup refusals for local-only settings.      |
 | `TENANT_PACKAGE_DIR` | `../examples/fintech`              | Tenant package directory, resolved from `server/`.                  |
 | `DEPLOYMENT_ID`      | the tenant package's id            | Names this deployment inside a shared Intelligence project.          |
diff --git a/scripts/start.sh b/scripts/start.sh
index 5f8ad63..75f185f 100755
--- a/scripts/start.sh
+++ b/scripts/start.sh
@@ -26,7 +26,9 @@ setting() {
 }
 
 APP_PORT="$(setting APP_PORT 3010)"
-SERVER_PORT="$(setting SERVER_PORT 3001)"
+# The documented name first, then PORT, matching the API process. An existing .env that only
+# renamed PORT would otherwise have start.sh health-checking 3001 while the server listened elsewhere.
+SERVER_PORT="$(setting SERVER_PORT "$(setting PORT 3001)")"
 COMPUTER_PORT="$(setting COMPUTER_PORT 4100)"
 BOT_PORT="$(setting BOT_PORT 4200)"
 LANGGRAPH_PORT="$(setting LANGGRAPH_PORT 4201)"
diff --git a/server/src/index.ts b/server/src/index.ts
index 3fc067a..4506c48 100644
--- a/server/src/index.ts
+++ b/server/src/index.ts
@@ -37,6 +37,7 @@ import {
   resolveModelApiKey,
 } from "./credentials";
 import { createDatabase } from "./db/client";
+import { resolveListenPort } from "./listen-port";
 import { createPluginStore } from "./plugins/store";
 import {
   createPackageStatusReader,
@@ -103,7 +104,7 @@ const identifyActor: IdentifyActor = async (request) => {
 };
 
 const config = loadConfig();
-const port = Number.parseInt(process.env.PORT ?? "3001", 10);
+const port = resolveListenPort();
 const database = createDatabase(config.databaseUrl);
 await initializeDevActorUser(database, config.devNoAuth);
 // The vault, built before the agent store because a customer's agent may sit behind a key and that
diff --git a/server/src/listen-port.ts b/server/src/listen-port.ts
new file mode 100644
index 0000000..1a61f36
--- /dev/null
+++ b/server/src/listen-port.ts
@@ -0,0 +1,16 @@
+/**
+ * Where this process should listen.
+ *
+ * The ports table, `scripts/start.sh`, and the Vite `/api` proxy all name `SERVER_PORT`. The process
+ * used to read only `PORT`, which is what `.env.example` used to set, so a clone that followed the
+ * docs moved the proxy and the health check but not the listener.
+ *
+ * `SERVER_PORT` first, then `PORT`, then 3001. Existing files that only set `PORT` keep working.
+ */
+export function resolveListenPort(
+  environment: Record<string, string | undefined> = process.env,
+): number {
+  const raw =
+    environment.SERVER_PORT?.trim() || environment.PORT?.trim() || "3001";
+  return Number.parseInt(raw, 10);
+}
diff --git a/server/tests/listen-port.test.ts b/server/tests/listen-port.test.ts
new file mode 100644
index 0000000..a744d25
--- /dev/null
+++ b/server/tests/listen-port.test.ts
@@ -0,0 +1,25 @@
+import { describe, expect, test } from "bun:test";
+import { resolveListenPort } from "../src/listen-port";
+
+describe("API listen port", () => {
+  test("defaults to 3001", () => {
+    expect(resolveListenPort({})).toBe(3001);
+  });
+
+  test("honours PORT, which existing .env files already set", () => {
+    expect(resolveListenPort({ PORT: "4001" })).toBe(4001);
+  });
+
+  test("honours SERVER_PORT, which is the name the docs and start.sh use", () => {
+    expect(resolveListenPort({ SERVER_PORT: "4002" })).toBe(4002);
+  });
+
+  test("prefers SERVER_PORT when both are set, so the documented name actually moves the listener", () => {
+    expect(resolveListenPort({ SERVER_PORT: "4002", PORT: "3001" })).toBe(4002);
+  });
+
+  test("treats blank values as unset", () => {
+    expect(resolveListenPort({ SERVER_PORT: "  ", PORT: "4001" })).toBe(4001);
+    expect(resolveListenPort({ SERVER_PORT: "", PORT: "" })).toBe(3001);
+  });
+});