diff --git a/scripts/server.mjs b/scripts/server.mjs
index 542ca44..3f35430 100644
--- a/scripts/server.mjs
+++ b/scripts/server.mjs
@@ -68,10 +68,7 @@ async function main() {
   await build();
 
   // start Zotero
-  startZotero();
-  setTimeout(() => {
-    openDevTool();
-  }, 5000);
+  startZotero(openDevTool);
 
   // watch
   await watch();
diff --git a/scripts/start.mjs b/scripts/start.mjs
index 2b9782b..b916b5a 100644
--- a/scripts/start.mjs
+++ b/scripts/start.mjs
@@ -10,6 +10,9 @@ import { exit } from "process";
 const { addonID } = details.config;
 const { zoteroBinPath, profilePath, dataDir } = cmd.exec;
 
+// Keep in sync with the addon's onStartup
+const loadDevToolWhen = `Plugin ${addonID} startup`;
+
 const logPath = "logs";
 const logFilePath = path.join(logPath, "zotero.log");
 
@@ -68,7 +71,9 @@ function prepareLog() {
   writeFileSync(logFilePath, "");
 }
 
-export function main() {
+export function main(callback) {
+  let isZoteroReady = false;
+
   prepareDevEnv();
 
   prepareLog();
@@ -81,6 +86,10 @@ export function main() {
   ]);
 
   zoteroProcess.stdout.on("data", (data) => {
+    if (!isZoteroReady && data.toString().includes(loadDevToolWhen)) {
+      isZoteroReady = true;
+      callback();
+    }
     writeFileSync(logFilePath, data, {
       flag: "a",
     });
diff --git a/src/hooks.ts b/src/hooks.ts
index 7b000f9..9b781f3 100644
--- a/src/hooks.ts
+++ b/src/hooks.ts
@@ -16,6 +16,14 @@ async function onStartup() {
     Zotero.unlockPromise,
     Zotero.uiReadyPromise,
   ]);
+
+  // TODO: Remove this after zotero#3387 is merged
+  if (__env__ === "development") {
+    // Keep in sync with the scripts/startup.mjs
+    const loadDevToolWhen = `Plugin ${config.addonID} startup`;
+    ztoolkit.log(loadDevToolWhen);
+  }
+
   initLocale();
 
   BasicExampleFactory.registerPrefs();