diff --git a/features/core.feature b/features/core.feature
index e5740b93..653e377c 100644
--- a/features/core.feature
+++ b/features/core.feature
@@ -23,6 +23,7 @@ Feature: Manage WordPress installation
 
     When I try `wp core is-installed`
     Then the return code should be 1
+    And STDERR should match /WordPress is not installed[\s\S]*Missing tables:.*\b[^\s_]+_/
 
     When I try `wp core is-installed --network`
     Then the return code should be 1
diff --git a/src/Core_Command.php b/src/Core_Command.php
index 3dd85bf6..d5b28c0b 100644
--- a/src/Core_Command.php
+++ b/src/Core_Command.php
@@ -2,7 +2,7 @@
 
 use Composer\Semver\Comparator;
 use WP_CLI\Extractor;
-use WP_CLI\Iterators\Table as TableIterator;
+use WP_CLI\Iterators\Table;
 use WP_CLI\Utils;
 use WP_CLI\Formatter;
 use WP_CLI\WpOrgApi;
@@ -393,11 +393,89 @@ function () use ( $temp ) {
 	 * @param array{network?: bool} $assoc_args Associative arguments.
 	 */
 	public function is_installed( $args, $assoc_args ) {
-		if ( is_blog_installed() && ( ! Utils\get_flag_value( $assoc_args, 'network' ) || is_multisite() ) ) {
+		try {
+			if ( ! is_blog_installed() ) {
+				WP_CLI::halt( 1 );
+			}
+
+			if ( Utils\get_flag_value( $assoc_args, 'network' ) && ! is_multisite() ) {
+				WP_CLI::halt( 1 );
+			}
+
+			global $wpdb;
+
+			// Get all tables including multisite if needed
+			$tables = $wpdb->tables( 'all', true );
+			$missing_tables = [];
+
+			// Check if we're using SQLite - check multiple possible indicators
+			$is_sqlite = (
+				( isset( $wpdb->dbdriver ) && 'sqlite' === $wpdb->dbdriver ) ||
+				( defined( 'DB_DRIVER' ) && 'sqlite' === DB_DRIVER ) ||
+				( defined( 'DB_ENGINE' ) && 'sqlite' === DB_ENGINE ) ||
+				( is_string( DB_HOST ) && ( strpos( DB_HOST, 'sqlite' ) !== false ) )
+			);
+
+			if ( defined( 'WP_CLI_TEST' ) && WP_CLI_TEST ) {
+				WP_CLI::debug( 'Database type: ' . ( $is_sqlite ? 'SQLite' : 'MySQL/MariaDB' ) );
+			}
+
+			foreach ( $tables as $table ) {
+				$table_name = $wpdb->prefix . $table;
+				
+				try {
+					try {
+						if ( $is_sqlite ) {
+							// SQLite uses a simpler table existence check
+							$result = $wpdb->get_var(
+								$wpdb->prepare(
+									"SELECT name FROM sqlite_master WHERE type='table' AND name=%s",
+									$table_name
+								)
+							);
+						} else {
+							// Standard MySQL/MariaDB check
+							$result = $wpdb->get_var(
+								$wpdb->prepare(
+									'SHOW TABLES LIKE %s',
+									$table_name
+								)
+							);
+						}
+					} catch ( Exception $e ) {
+						// If there's an error, assume the table doesn't exist
+						$result = null;
+					}
+
+					if ( defined( 'WP_CLI_TEST' ) && WP_CLI_TEST ) {
+						WP_CLI::debug( sprintf( 'Table %s: %s', $table_name, $result ? 'exists' : 'missing' ) );
+					}
+
+					if ( $result !== $table_name ) {
+						$missing_tables[] = $table_name;
+					}
+				} catch ( Exception $e ) {
+					WP_CLI::debug( sprintf( 'Error checking table %s: %s', $table_name, $e->getMessage() ) );
+					$missing_tables[] = $table_name;
+				}
+			}
+
+			if ( ! empty( $missing_tables ) ) {
+				WP_CLI::error(
+					sprintf(
+						'WordPress is not installed. Missing tables: %s',
+						implode( ', ', $missing_tables )
+					),
+					1
+				);
+			}
+
 			WP_CLI::halt( 0 );
-		}
 
-		WP_CLI::halt( 1 );
+		} catch ( Exception $e ) {
+			WP_CLI::debug( 'Error in is_installed: ' . $e->getMessage() );
+			WP_CLI::halt( 1 );
+		}
 	}
 
 	/**
diff --git a/wp-cli.phar b/wp-cli.phar
new file mode 100644
index 00000000..4432e71d
Binary files /dev/null and b/wp-cli.phar differ