diff --git a/packages/phpcs-standards/SiteKit/Sniffs/Commenting/DocCommentFullStopSniff.php b/packages/phpcs-standards/SiteKit/Sniffs/Commenting/DocCommentFullStopSniff.php
new file mode 100644
index 00000000000..f908271afc1
--- /dev/null
+++ b/packages/phpcs-standards/SiteKit/Sniffs/Commenting/DocCommentFullStopSniff.php
@@ -0,0 +1,182 @@
+<?php
+/**
+ * DocCommentFullStopSniff
+ *
+ * @package Google\Site_Kit\Sniffs\Commenting
+ */
+
+namespace Google\Site_Kit\Sniffs\Commenting;
+
+use PHP_CodeSniffer\Files\File;
+use PHP_CodeSniffer\Sniffs\Sniff;
+
+/**
+ * Ensures that PHPDoc short descriptions and inline comments end with a full stop.
+ */
+class DocCommentFullStopSniff implements Sniff {
+
+	/**
+	 * Tokens this sniff listens for.
+	 *
+	 * @return array
+	 */
+	public function register() {
+		return array(
+			T_FUNCTION,
+			T_CLASS,
+			T_INTERFACE,
+			T_TRAIT,
+			T_VARIABLE,
+			T_CONST,
+			T_COMMENT,
+		);
+	}
+
+	/**
+	 * Process tokens.
+	 *
+	 * @param File $phpcs_file The file being scanned.
+	 * @param int  $stack_ptr  Current token position.
+	 * @return void
+	 */
+	public function process( File $phpcs_file, $stack_ptr ) {
+		$tokens = $phpcs_file->getTokens();
+		$token  = $tokens[ $stack_ptr ]['code'];
+
+		// Handle inline comments separately.
+		if ( T_COMMENT === $token ) {
+			$this->check_inline_comment( $phpcs_file, $stack_ptr );
+			return;
+		}
+
+		// For PHPDoc: check if immediately before this element is a docblock.
+		$find = array(
+			T_WHITESPACE,
+			T_ABSTRACT,
+			T_FINAL,
+			T_PUBLIC,
+			T_PROTECTED,
+			T_PRIVATE,
+			T_STATIC,
+			T_VAR,
+		);
+
+		$comment_end = $phpcs_file->findPrevious( $find, ( $stack_ptr - 1 ), null, true );
+		if ( false === $comment_end || T_DOC_COMMENT_CLOSE_TAG !== $tokens[ $comment_end ]['code'] ) {
+			return;
+		}
+
+		$comment_start = $tokens[ $comment_end ]['comment_opener'];
+
+		// Collect the short summary (all lines before a blank or @tag).
+		$summary_line_ptrs = array();
+		for ( $i = ( $comment_start + 1 ); $i < $comment_end; $i++ ) {
+			$code = $tokens[ $i ]['code'];
+
+			if ( T_DOC_COMMENT_STRING === $code ) {
+				$content = trim( $tokens[ $i ]['content'] );
+				if ( '' === $content ) {
+					break;
+				}
+				if ( 0 === strpos( $content, '@' ) ) {
+					break;
+				}
+				$summary_line_ptrs[] = $i;
+				continue;
+			}
+
+			if ( T_DOC_COMMENT_TAG === $code ) {
+				break;
+			}
+		}
+
+		if ( array() === $summary_line_ptrs ) {
+			return;
+		}
+
+		$last_ptr     = end( $summary_line_ptrs );
+		$last_content = trim( $tokens[ $last_ptr ]['content'] );
+
+		if ( false === $this->needs_full_stop( $last_content ) ) {
+			return;
+		}
+
+		$error = 'PHPDoc summary must end with a full stop.';
+		$fix   = $phpcs_file->addFixableError( $error, $last_ptr, 'MissingFullStop' );
+
+		if ( true === $fix ) {
+			$phpcs_file->fixer->replaceToken( $last_ptr, rtrim( $tokens[ $last_ptr ]['content'] ) . '.' );
+		}
+	}
+
+	/**
+	 * Check inline comments for full stop.
+	 *
+	 * @param File $phpcs_file The file being scanned.
+	 * @param int  $stack_ptr  Current token position.
+	 * @return void
+	 */
+	private function check_inline_comment( File $phpcs_file, int $stack_ptr ): void {
+		$tokens = $phpcs_file->getTokens();
+
+		// Only process if this is the first line of a contiguous // comment block.
+		$prev = $stack_ptr - 1;
+		if ( $prev >= 0 && T_COMMENT === $tokens[ $prev ]['code'] && 0 === strpos( trim( $tokens[ $prev ]['content'] ), '//' ) ) {
+			return;
+		}
+
+		// Collect this block (current + any following // lines).
+		$block_ptrs = array( $stack_ptr );
+		$next       = $stack_ptr + 1;
+		$total      = \count( $tokens );
+
+		while ( $next < $total && T_COMMENT === $tokens[ $next ]['code'] && 0 === strpos( trim( $tokens[ $next ]['content'] ), '//' ) ) {
+			$block_ptrs[] = $next;
+			++$next;
+		}
+
+		// Take the last non-empty line in this block.
+		$last_ptr = null;
+		foreach ( array_reverse( $block_ptrs ) as $ptr ) {
+			$content = trim( preg_replace( '#^/{2,}\s*#', '', $tokens[ $ptr ]['content'] ) );
+			if ( '' !== $content ) {
+				$last_ptr = $ptr;
+				break;
+			}
+		}
+
+		if ( null === $last_ptr ) {
+			return;
+		}
+
+		$last_content = trim( preg_replace( '#^/{2,}\s*#', '', $tokens[ $last_ptr ]['content'] ) );
+
+		// Skip annotation-like comments (e.g. @todo, @phpcs).
+		if ( 0 === strpos( $last_content, '@' ) ) {
+			return;
+		}
+
+		if ( false === $this->needs_full_stop( $last_content ) ) {
+			return;
+		}
+
+		$error = 'Inline comment must end with a full stop.';
+		$fix   = $phpcs_file->addFixableError( $error, $last_ptr, 'InlineMissingFullStop' );
+
+		if ( true === $fix ) {
+			$new = rtrim( $tokens[ $last_ptr ]['content'] ) . '.';
+			$phpcs_file->fixer->replaceToken( $last_ptr, $new );
+		}
+	}
+
+	/**
+	 * Check if text needs a full stop.
+	 *
+	 * @param string $text The text to check.
+	 * @return bool True if a full stop is needed, false otherwise.
+	 */
+	private function needs_full_stop( string $text ): bool {
+		// Ignore if it already ends correctly.
+		return ( 1 !== preg_match( '/[.?!]$/u', $text ) );
+	}
+}
diff --git a/phpcs.xml b/phpcs.xml
index 40cdefaa167..d07c6e2fcba 100644
--- a/phpcs.xml
+++ b/phpcs.xml
@@ -61,6 +61,7 @@
 
 	<!-- Custom Site Kit rules -->
 	<rule ref="SiteKit.PHPUnit.RequireAssertionMessage"/>
+	<rule ref="SiteKit.Commenting.DocCommentFullStop"/>
 
 	<!-- Show details about violated sniffs -->
 	<arg value="s"/>