Digital Index of Middle English Verse. A fine free resource and the record pages are extensive, but regrettably it has a search interface that only a librarian could love. There’s no dedicated keyword search, and only fairly limited topic tagging. If you want all poems mentioning a “star” but not Jesus, for instance, you have to do a Google site: search.
Opening lines of a prayer to the Morning Star and against the plague, England c. 15th century (modern English):
O heavenly star, most comfortable of light,
Which, with your ghostly gracious influence,
Has clarified and put to flight
All misty weathers perilous for pestilence.