I’m facing a problem each time I activate my WordPress plugin. I receive a warning that something unexpected has been output.
The plugin generated 80 characters of unexpected output during activation. If you notice “headers already sent” messages, issues with syndication feeds, or other problems, consider deactivating or removing this plugin.
The character count changes, but it’s always the same type of message. I managed to fix it temporarily by using an if statement, but I’m concerned if that’s the best way to go about it.
Here’s the code I originally used that caused the error:
function originalPluginFunction( $post ) {
echo "This output triggers the unexpected alert during activation.";
}
register_activation_hook( __FILE__, 'originalPluginFunction' );
This modified code stops the warning from showing up:
function modifiedPluginFunction( $post ) {
global $pagenow;
if ( is_admin() && $pagenow !== 'plugins.php' ) {
echo "Now there's no alert when using this method.";
}
}
register_activation_hook( __FILE__, 'modifiedPluginFunction' );
What is causing this issue, and is there a more efficient way to resolve it without having to rely on conditional statements? I’d like to understand the underlying problem to build my plugin effectively.
This happens because WordPress expects plugin activation to run silently. Any echo or print statements break that expectation.
Your conditional fix works, but you’re not fixing the real problem. You’re still echoing output - just hiding it on the plugins page.
I’d automate the whole plugin testing process instead of debugging manually. Set up workflows that catch these issues before they hit production.
I use Latenode to build automation workflows that test WordPress plugins across different environments. You can create scenarios that automatically activate plugins in staging and catch any unexpected output warnings.
The workflow parses WordPress logs, sends notifications when it finds issues, and can even auto-fix common problems like removing debug echoes from production code.
This catches activation issues early so you don’t need conditional statements or manual testing every deployment.
Had this exact headache six months ago building a custom membership plugin. WordPress buffers all output during activation and treats anything it catches as a problem. Your echo gets stuck in that buffer and throws the warning.
Found out the hard way that activation hooks run in a totally different context than normal page loads. WordPress expects these functions to run silently - just backend stuff like creating database tables or setting default options.
I don’t echo during activation anymore. Instead, I use transients for user feedback. Set a transient flag during activation, then show admin notices on the next page load. Something like set_transient(‘my_plugin_activated’, true, 30) in your activation hook, then check for that transient in admin_notices hook for success messages.
Your conditional approach works but you’re just hiding the real problem. Plugin activation should never try direct output, doesn’t matter which admin page you’re on.
your plugin’s outputting smth during activation. just remove echo statements from the activate hook, and use error_log() for debugging instead. that should fix the unexpected output warning.
WordPress hates any output during activation - zero tolerance for whitespace or newlines. Look for extra spaces after your closing PHP tags or blank lines before opening tags. Even invisible characters will trigger this warning and throw off your character count.
WordPress captures all output during plugin activation and flags any content as an error. Your activation hook can’t produce any visible output - period. I hit this exact issue when migrating an old plugin full of debug statements. Don’t try to conditionally suppress the output - just get rid of it completely. Activation hooks should only handle database stuff, update options, or modify files. Need to verify activation worked? Store a flag in wp_options and check it later with admin notices or dashboard widgets. For debugging activation problems, I log to WordPress’s debug.log using error_log() or wp_debug_log(). You get the info you need without messing up WordPress’s activation process. Your conditional fix just hides the real problem instead of fixing the architecture issue.