MyBB is a free and open source forum software. This is the simple yet powerful one. MyBB is well optimized for search engine. But the only problem is that it does provide robots.txt file to guide the search engine robots. We recommend the following robots.txt file for any MyBB forum software.

In case, your MyBB ACP -> Configuration -> Server and Optimization Options -> Enable search engine friendly URLs? is set to DISABLED then use the following robots.txt:-

User-Agent: *
Disallow: /moderation.php
Disallow: /ratethread.php
Disallow: /report.php
Disallow: /reputation.php
Disallow: /sendthread.php
Disallow: /usercp.php
Disallow: /usercp2.php
Disallow: /newreply.php
Disallow: /newthread.php
Disallow: /editpost.php
Disallow: /private.php
Disallow: /task.php
Disallow: /search.php
Disallow: /stats.php
Disallow: /member.php
Disallow: /memberlist.php
Disallow: /showteam.php
Disallow: /showratings.php
Disallow: /syndication.php

In case, your MyBB ACP -> Configuration -> Server and Optimization Options -> Enable search engine friendly URLs? is set to ENABLED then use the following robots.txt:-

User-agent: *
Disallow: /archive/
Disallow: /private.php*
Disallow: /usercp.php
Disallow: /usercp2.php
Disallow: /ratethread.php
Disallow: /newreply.php
Disallow: /memberlist.php
Disallow: /printthread.php
Disallow: /forumdisplay.php
Disallow: /showthread.php
Disallow: /member.php
Disallow: /calendar.php
Disallow: /newthread.php
Disallow: /editpost.php
Disallow: /moderation.php
Disallow: /report.php
Disallow: /reputation.php
Disallow: /sendthread.php
Disallow: /task.php
Disallow: /search.php
Disallow: /stats.php
Disallow: /showteam.php
Disallow: /showratings.php
Disallow: /syndication.php
Disallow: /thread-*-lastpost.html
Disallow: /thread-*-nextnewest.html
Disallow: /thread-*-nextoldest.html
Disallow: /thread-*-newpost.html
Disallow: /thread-*-post-*.html
Disallow: /post-*.html
Disallow: /forum-*.html?datecut=9999