Alliteration
Checker.Initial sounds, mapped

Alliteration is repeated initial consonant sounds in words near each other. Sound is the operative word. 'Known nothing' alliterates, because k-n and plain n both open on the same n sound; 'city cat' does not, because soft c opens on s while hard c opens on k. Any definition that works from letters will get both of those wrong, and English spelling supplies an endless list of similar traps: phone and foam, wren and run, psalm and song.

Proximity matters as much as sound. Two b-words ten lines apart are not a device; two in the same breath are. Most readers place the boundary somewhere around a line or a clause, which is why this checker groups words within each line rather than across a whole poem.

Alliteration has two siblings. Assonance repeats vowel sounds ('the rain in Spain'), consonance repeats consonants anywhere but the front ('pitter patter'). This tool reads the front of the word only, so vowel-initial words are excluded by design — repetition of opening vowels belongs to assonance.

Each word passes through a spelling-to-sound mapping before comparison. Digraphs keep their identity: ship and shore group on sh, not on s. Silent openings are stripped, so knight sits with night and wrist with rest. Ph becomes f, qu becomes k, and c splits by context — soft before e, i, or y, hard everywhere else.

S-clusters get a deliberate ruling. Street and strong group together on str, but street and sun stay apart: an s followed by a stop consonant reads as its own onset, and pairing 'street' with 'sun' would flag alliteration your ear doesn't hear. Looser clusters go the other way — bright, blue, and bird all alliterate on b, as they always have in the classical account of the device.

Two honest limits. The mapper works from spelling, so an ambiguous opening like soft g is left as g rather than guessed at. And it cannot hear stress: it will flag a run of function words — 'the', 'that', 'this' — that your ear skips right over because nothing lands on them. Treat the readout as a map of candidates, and keep the final call yourself.

For the first several centuries of English poetry, alliteration was not decoration — it was the structure. Beowulf has no rhyme scheme; each line binds its two halves by repeating an initial sound across the stresses. When rhyme arrived from the continent it took over the structural job, and alliteration moved to the texture layer, where it has stayed.

The tongue-twister is the device pushed to failure on purpose. 'Peter Piper' and 'she sells sea shells' pile up onsets faster than the mouth can reset, which is the whole game. Poets run the same engine at lower revs: Coleridge's 'The fair breeze blew, the white foam flew' uses paired f and b sounds to make the ship's speed audible.

Modern poets reach for it when they want a phrase to fasten itself to memory, or when a passage needs binding that rhyme would make too loud. A little goes far. If the checker lights up every line of your draft, that is usually the note to take.