diff --git a/src/config.js b/src/config.js
index ed9a25a..8609562 100644
--- a/src/config.js
+++ b/src/config.js
@@ -10,8 +10,14 @@ function intFromEnv(name, fallback) {
   return Number.isInteger(parsed) ? parsed : fallback;
 }
 
+function strFromEnv(name, fallback) {
+  const raw = process.env[name];
+  return raw && String(raw).trim() ? String(raw).trim() : fallback;
+}
+
 const config = {
   port: intFromEnv("PORT", 3000),
+  stateFilePath: strFromEnv("STATE_FILE_PATH", "./data/state.json"),
   xWebhookSecret: process.env.X_WEBHOOK_SECRET || "dev-x-secret",
   polarWebhookSecret: process.env.POLAR_WEBHOOK_SECRET || "dev-polar-secret",
   credit: {
diff --git a/test/config.test.js b/test/config.test.js
new file mode 100644
index 0000000..ab8218d
--- /dev/null
+++ b/test/config.test.js
@@ -0,0 +1,60 @@
+"use strict";
+
+const test = require("node:test");
+const assert = require("node:assert/strict");
+
+test("config uses defaults when env is missing", () => {
+  const previous = {
+    PORT: process.env.PORT,
+    STATE_FILE_PATH: process.env.STATE_FILE_PATH,
+  };
+
+  delete process.env.PORT;
+  delete process.env.STATE_FILE_PATH;
+
+  delete require.cache[require.resolve("../src/config")];
+  const { config } = require("../src/config");
+
+  assert.equal(config.port, 3000);
+  assert.equal(config.stateFilePath, "./data/state.json");
+
+  if (previous.PORT === undefined) {
+    delete process.env.PORT;
+  } else {
+    process.env.PORT = previous.PORT;
+  }
+
+  if (previous.STATE_FILE_PATH === undefined) {
+    delete process.env.STATE_FILE_PATH;
+  } else {
+    process.env.STATE_FILE_PATH = previous.STATE_FILE_PATH;
+  }
+});
+
+test("config reads state path and numeric env overrides", () => {
+  const previous = {
+    PORT: process.env.PORT,
+    STATE_FILE_PATH: process.env.STATE_FILE_PATH,
+  };
+
+  process.env.PORT = "8080";
+  process.env.STATE_FILE_PATH = "/data/prod-state.json";
+
+  delete require.cache[require.resolve("../src/config")];
+  const { config } = require("../src/config");
+
+  assert.equal(config.port, 8080);
+  assert.equal(config.stateFilePath, "/data/prod-state.json");
+
+  if (previous.PORT === undefined) {
+    delete process.env.PORT;
+  } else {
+    process.env.PORT = previous.PORT;
+  }
+
+  if (previous.STATE_FILE_PATH === undefined) {
+    delete process.env.STATE_FILE_PATH;
+  } else {
+    process.env.STATE_FILE_PATH = previous.STATE_FILE_PATH;
+  }
+});