diff --git a/README.md b/README.md
index 798f7d5..22bc38d 100644
--- a/README.md
+++ b/README.md
@@ -314,6 +314,19 @@ To update the tags:
 ./vendor/bin/tailor ter:update my_extension --tags=some-tag,another-tag
 ```
 
+Tags are what people search the extension listing by, so they are worth
+choosing for TER specifically. Every extension in TER is a TYPO3 extension,
+which means terms such as `typo3`, `typo3-extension`, `extension`, `cms` or
+`php` narrow nothing down there — even though the very same terms are what
+make a package findable on GitHub or Packagist. Prefer tags describing what
+the extension does. Tailor warns when it recognises such a term, but still
+sends whatever you pass.
+
+This matters most for automated publishing: because the whole list is
+replaced on every call (see below), a pipeline that reuses one vocabulary
+across registries will keep overwriting curated TER tags with terms that add
+nothing.
+
 Please use `./vendor/bin/tailor ter:update -h` to see the full
 list of available options.
 
diff --git a/src/Command/Extension/UpdateExtensionCommand.php b/src/Command/Extension/UpdateExtensionCommand.php
index ab70fdf..5787076 100644
--- a/src/Command/Extension/UpdateExtensionCommand.php
+++ b/src/Command/Extension/UpdateExtensionCommand.php
@@ -16,6 +16,7 @@
 use Symfony\Component\Console\Input\InputInterface;
 use Symfony\Component\Console\Input\InputOption;
 use Symfony\Component\Console\Output\OutputInterface;
+use Symfony\Component\Console\Style\SymfonyStyle;
 use TYPO3\Tailor\Command\AbstractClientRequestCommand;
 use TYPO3\Tailor\Dto\Messages;
 use TYPO3\Tailor\Dto\RequestConfiguration;
@@ -51,15 +52,49 @@ protected function configure(): void
             ->addOption('repository', '', InputOption::VALUE_OPTIONAL, 'Link to the repository')
             ->addOption('manual', '', InputOption::VALUE_OPTIONAL, 'Link to the external manual')
             ->addOption('paypal', '', InputOption::VALUE_OPTIONAL, 'Link to sponsoring page (paypal)')
-            ->addOption('tags', '', InputOption::VALUE_OPTIONAL, 'Comma-separated list of tags');
+            ->addOption(
+                'tags',
+                '',
+                InputOption::VALUE_OPTIONAL,
+                'Comma-separated list of tags. Replaces the existing list. Every extension in TER is a '
+                . 'TYPO3 extension, so terms like typo3, typo3-extension, extension or php add no '
+                . 'discoverability there - prefer tags describing what the extension does.'
+            );
     }
 
     protected function execute(InputInterface $input, OutputInterface $output): int
     {
         $this->extensionKey = CommandHelper::getExtensionKeyFromInput($input);
+        $this->warnAboutTagsImpliedByTer($input, $output);
+
         return parent::execute($input, $output);
     }
 
+    /**
+     * TER replaces the whole tag list with what is sent, so a pipeline reusing
+     * one vocabulary across registries silently publishes terms that say
+     * nothing here. Point them out without changing what gets sent.
+     */
+    private function warnAboutTagsImpliedByTer(InputInterface $input, OutputInterface $output): void
+    {
+        $tags = $input->getOption('tags');
+        if (!is_string($tags) || $tags === '') {
+            return;
+        }
+
+        $implied = CommandHelper::getTagsImpliedByTer($tags);
+        if ($implied === []) {
+            return;
+        }
+
+        (new SymfonyStyle($input, $output))->warning(sprintf(
+            'Every extension in TER is a TYPO3 extension, so %s %s no discoverability there. '
+            . 'Consider tags describing what the extension does instead.',
+            implode(', ', $implied),
+            count($implied) === 1 ? 'adds' : 'add'
+        ));
+    }
+
     protected function getRequestConfiguration(): RequestConfiguration
     {
         return new RequestConfiguration(
diff --git a/src/Helper/CommandHelper.php b/src/Helper/CommandHelper.php
index d3a516b..f15a806 100644
--- a/src/Helper/CommandHelper.php
+++ b/src/Helper/CommandHelper.php
@@ -22,6 +22,31 @@
  */
 final class CommandHelper
 {
+    /**
+     * Terms every TER listing already implies. TER only lists TYPO3 extensions,
+     * so these narrow nothing down there — unlike on GitHub or Packagist, where
+     * the same terms are what make a package findable at all.
+     *
+     * Compared after stripping separators, so the spelling variants that occur
+     * in practice — "typo3 cms" in composer.json keywords, "typo3-cms-extension"
+     * in GitHub topics — are all recognised.
+     *
+     * @var string[]
+     */
+    private const TAGS_IMPLIED_BY_TER = [
+        'cms',
+        'cmsextension',
+        'extension',
+        'extensions',
+        'php',
+        'ter',
+        'typo3',
+        'typo3cms',
+        'typo3cmsextension',
+        'typo3ext',
+        'typo3extension',
+    ];
+
     public static function getExtensionKeyFromInput(InputInterface $input): string
     {
         // 1. CLI argument has highest priority
@@ -52,4 +77,29 @@ public static function getExtensionKeyFromInput(InputInterface $input): string
             1605706548
         );
     }
+
+    /**
+     * Returns those of the given tags that TER already implies, so the caller
+     * can point them out. Case and separators are ignored.
+     *
+     * @return string[]
+     */
+    public static function getTagsImpliedByTer(string $tags): array
+    {
+        $implied = [];
+
+        foreach (explode(',', $tags) as $tag) {
+            $tag = trim($tag);
+            if ($tag === '') {
+                continue;
+            }
+
+            $normalized = strtolower((string)preg_replace('/[^a-z0-9]/i', '', $tag));
+            if (in_array($normalized, self::TAGS_IMPLIED_BY_TER, true)) {
+                $implied[] = $tag;
+            }
+        }
+
+        return $implied;
+    }
 }
diff --git a/tests/Unit/Helper/CommandHelperTest.php b/tests/Unit/Helper/CommandHelperTest.php
index c805a21..894d4aa 100644
--- a/tests/Unit/Helper/CommandHelperTest.php
+++ b/tests/Unit/Helper/CommandHelperTest.php
@@ -12,6 +12,7 @@
 
 namespace TYPO3\Tailor\Tests\Unit\Helper;
 
+use PHPUnit\Framework\Attributes\DataProvider;
 use PHPUnit\Framework\Attributes\Test;
 use PHPUnit\Framework\TestCase;
 use Symfony\Component\Console\Input\ArrayInput;
@@ -98,4 +99,42 @@ public function getExtensionKeyFromInputReturnsExtensionKeyFromEnvironmentVariab
             restore_error_handler();
         }
     }
+
+    /**
+     * @param string[] $expected
+     */
+    #[Test]
+    #[DataProvider('tagsImpliedByTerDataProvider')]
+    public function getTagsImpliedByTerReturnsOnlyTermsTerAlreadyImplies(string $tags, array $expected): void
+    {
+        self::assertSame($expected, CommandHelper::getTagsImpliedByTer($tags));
+    }
+
+    /**
+     * @return array<string, array{0: string, 1: string[]}>
+     */
+    public static function tagsImpliedByTerDataProvider(): array
+    {
+        return [
+            'empty input' => ['', []],
+            'only domain tags' => ['search,indexing,facets', []],
+            'single implied tag' => ['typo3,search', ['typo3']],
+            'several implied tags' => ['typo3,php,search,extension', ['typo3', 'php', 'extension']],
+            'case is ignored' => ['TYPO3,Extension', ['TYPO3', 'Extension']],
+            'surrounding whitespace' => [' typo3 , search ', ['typo3']],
+            'empty segments' => ['typo3,,search,', ['typo3']],
+            'substring is not a match' => ['typo3-solr,phpunit', []],
+            // Spelling variants observed in the wild: composer.json keywords
+            // favour "typo3 cms", GitHub topics "typo3-cms-extension".
+            'separator variants' => [
+                'typo3 cms,typo3-cms,typo3cms',
+                ['typo3 cms', 'typo3-cms', 'typo3cms'],
+            ],
+            'extension variants' => [
+                'typo3-cms-extension,typo3-extension,cms-extension',
+                ['typo3-cms-extension', 'typo3-extension', 'cms-extension'],
+            ],
+            'domain tag with separator survives' => ['e-commerce,tt_news', []],
+        ];
+    }
 }