Sonnet 99 is one of only three irregular sonnets in Shakespeare's sequence (the others being Sonnet 126 which structurally is not a sonnet at all but rather a poem of six pentameter couplets, and Sonnet 145 which has the typical rhyme scheme but is written in iambic tetrameter). Whereas a typical English or Shakespearean sonnet has three quatrains, followed by a final rhyming couplet, with the rhyme scheme ABAB CDCD EFEF GG, this sonnet begins with a quintain yielding the rhyme scheme ABABA CDCD EFEF GG. Like the other sonnets (except Sonnet 145) it is composed in iambic pentameter, a type of poetic metre based on five pairs of metrically weak/strong syllabic positions. The 8th line exemplifies a regular iambic pentameter: