Iambic Pentameter
Checker.Scansion, line by line

An iamb is a two-syllable unit, unstressed then stressed: da-DUM. Iambic pentameter puts five of them in a row — da-DUM da-DUM da-DUM da-DUM da-DUM — for a line of ten syllables with the beat falling on the even positions. Take the opening of Sonnet 18: 'Shall I compare thee to a summer's day?' scans as shall-I com-PARE thee-TO a-SUM mer's-DAY, five clean iambs.

English falls into this rhythm because the language alternates naturally. Articles, prepositions, and pronouns tend to sit light; the nouns and verbs they attach to carry the weight. String ordinary English words together and a rough alternation of weak and strong syllables appears on its own. Pentameter takes that native pulse and holds it to a count, which is why the meter dominated English verse for five centuries and why unrhymed pentameter, blank verse, became the default line of the stage.

The tool looks up every word in the CMU pronouncing dictionary, a phonetic database of 134,000 English words, and reads the stress marked on each syllable. 'Compare' is fixed as com-PARE; 'temperate' as TEM-per-ate. Those stresses are pinned wherever the word lands in your line.

Monosyllables get different treatment. A word like 'thee' or 'and' takes its stress from context — promoted when the meter leans on it, demoted when it doesn't. A checker that marks monosyllables rigidly fails real Shakespeare on nearly every line, so this one marks them flexible and lets them satisfy either position.

A line passes when at least 80 percent of its fixed syllables sit where the iamb wants them. That threshold is deliberate. Strict 100-percent matching would fail legitimate substitutions, like a trochaic first foot, that poets have used since the meter existed. The readout shows every line's pattern so you can see exactly which syllables carried the verdict.

The most famous line in English drama has eleven syllables. 'To be, or not to be, that is the question' runs five iambs and then lets 'question' spill one unstressed syllable past the tenth. That extra soft syllable is a feminine ending, and it is standard pentameter practice, not an error. The checker gives it its own verdict rather than lumping it in with broken lines.

Substitution works the same way. Shakespeare regularly opens a line with a trochee, a flipped foot that stresses the first syllable ('Now is the winter of our discontent'), then settles back into iambs. An inversion like that is texture, a deliberate push against the pulse the rest of the line restores. Scansion exists to catch these choices, not to punish them, and a line that varies inside the pattern still scans.