Port already in use? How to fix it when your AI coding agent keeps starting servers

Description and use

<p>You ask your AI coding agent to run the app, and you get this:<br> </p> <div class="highlight js-code-highlight"> <pre class="highlight plaintext"><code>Error: listen EADDRINUSE: address already in use :::3000 </code></pre> </div> <p>Or worse, you don't get an error at all. The agent's server quietly starts on 3001, your browser is still on 3000, and you spend ten minutes wondering why your change isn't showing up.</p> <p>I wrote a general guide to <a href="https://dev.to/tjthouhid/whats-using-port-3000-on-my-mac-find-it-see-who-started-it-and-stop-it-safely-5h0i">finding and stopping whate

Problem

<p>You ask your AI coding agent to run the app, and you get this:<br> </p> <div class="highlight js-code-highlight"> <pre class="highlight plaintext"><code>Error: listen EADDRINUSE: address already in use :::3000 </code></pre> </div> <p>Or worse, you don't get an error at all. The agent's server quietly starts on 3001, your browser is still on 3000, and you spend ten minutes wondering why your change isn't showing up.</p> <p>I wrote a general guide to <a href="https://dev.to/tjthouhid/whats-using-port-3000-on-my-mac-find-it-see-who-started-it-and-stop-it-safely-5h0i">finding and stopping whate

Outcome

<p>You ask your AI coding agent to run the app, and you get this:<br> </p> <div class="highlight js-code-highlight"> <pre class="highlight plaintext"><code>Error: listen EADDRINUSE: address already in use :::3000 </code></pre> </div> <p>Or worse, you don't get an error at all. The agent's server quietly starts on 3001, your browser is still on 3000, and you spend ten minutes wondering why your change isn't showing up.</p> <p>I wrote a general guide to <a href="https://dev.to/tjthouhid/whats-using-port-3000-on-my-mac-find-it-see-who-started-it-and-stop-it-safely-5h0i">finding and stopping whate

Evidence

Port already in use? How to fix it when your AI coding agent keeps starting servers

Source