WordPress SEO

<?php
// No plugin ships this, so it is a rewrite rule plus a template redirect.
add_action('init', function () {
    add_rewrite_rule('^llms\.txt$', 'index.php?llms_txt=1', 'top');
});

add_filter('query_vars', function ($vars) {
    $vars[] = 'llms_txt';
    return $vars;
});

add_action('template_redirect', function () {
    if (!get_query_var('llms_txt')) {
        return;
    }
    header('Content-Type: text/plain; charset=utf-8');
    header('Cache-Control: public, max-age=3600, s-maxage=3600');

    $lines = [
        '# ' . get_bloginfo('name'),
        '',
        '> ' . get_bloginfo('description'),
        '',
        '## Key facts',
        '',
        '- Canonical site: ' . home_url(),
        '',
        '## What this is not',
        '',
        '- ' . get_bloginfo('name') . ' is not a marketplace.',
    ];
    echo implode("\n", $lines) . "\n";
    exit;
});

<?php
// Emitting your own graph while a plugin emits its own produces two scripts
// and two Organization nodes with different identifiers.
add_filter('wpseo_json_ld_output', '__return_false');

add_action('wp_head', function () {
    $graph = [
        '@context' => 'https://schema.org',
        '@graph' => [
            [
                '@type' => 'Organization',
                '@id' => home_url('/#organization'),
                'name' => get_bloginfo('name'),
                'url' => home_url('/'),
            ],
            [
                '@type' => 'WebSite',
                '@id' => home_url('/#website'),
                'url' => home_url('/'),
                'publisher' => ['@id' => home_url('/#organization')],
            ],
        ],
    ];
    printf(
        '<script type="application/ld+json">%s</script>',
        wp_json_encode($graph, JSON_UNESCAPED_SLASHES | JSON_HEX_TAG)
    );
}, 20);

<?php
// post_modified changes on every save, including a typo fix in a draft.
// Tracking a deliberate content-change timestamp keeps lastmod meaningful.
add_action('post_updated', function ($post_id, $post_after, $post_before) {
    if ($post_after->post_content !== $post_before->post_content) {
        update_post_meta($post_id, '_content_changed_at', current_time('mysql', true));
    }
}, 10, 3);

add_filter('wp_sitemaps_posts_entry', function ($entry, $post) {
    $changed = get_post_meta($post->ID, '_content_changed_at', true);
    $entry['lastmod'] = wp_date('c', strtotime($changed ?: $post->post_modified_gmt));
    return $entry;
}, 10, 2);

<?php
add_filter('robots_txt', function ($output, $public) {
    if (!$public) {
        return $output; // Site is set to discourage indexing. Respect it.
    }

    $deny = ['GPTBot', 'Google-Extended', 'CCBot', 'anthropic-ai', 'Bytespider'];
    $allow = ['OAI-SearchBot', 'ChatGPT-User', 'PerplexityBot', 'ClaudeBot'];

    foreach ($allow as $agent) {
        $output .= "\n# Citation crawler: sends referral traffic.\n";
        $output .= "User-agent: {$agent}\nAllow: /\nDisallow: /wp-admin/\n";
    }
    foreach ($deny as $agent) {
        $output .= "\n# Training crawler: no referral traffic.\n";
        $output .= "User-agent: {$agent}\nDisallow: /\n";
    }
    return $output;
}, 10, 2);