← All models Claude Sonnet 4.6 editing test Anthropic · Tested Oct 28, 2026 · 1m 25s · $0.30
Four checks All in one 55/90 caught
Grammar & spelling 34/45 Repetitions 6/15 Redundancy 6/15 Consistency 9/15 185 comments · 5 extra flags
Claude Sonnet 4.6 caught 55 of 90 planted mistakes, tied 15th of 16 models tested. It was strongest on grammar and spelling (34 of 45) and missed most on redundancies (6 of 15). The 4 checks took 1m 25s and cost $0.30; asked for all of them in one prompt, it caught 49.
Every comment Claude Sonnet 4.6 left on our 6,000-word test story, where it left it. Click a missed mistake to find it in the text. The checks come from icanwrite , a markdown editor for writers.
Missed · 35
who, not whom: subject of 'was' “whom she guessed was the owner” Misplaced modifier: bound nearly every “he had nearly bound every family Bible” any other shop: the bakery is on Wharf Street “longer than any shop on Wharf Street” Fragment: the survey has no verb “The survey from twelve years ago, which an engineer from the county” Missing auxiliary: had been “The fuse box by the back door been painted shut” Restrictive clause, no commas: the entries that held “The entries, which held only a single word, were” Past tense: led “Nora lead the way upstairs” in to, not into “turned his uniform into the quartermaster” an MBA: said 'em-bee-ay' “Daniel had a MBA” 'one of those who' takes a plural verb: were “one of the last binders in New England who was still” Comma splice “open on her chest, she woke at dawn” Distinctive, chapters apart: pewter “Pewter light from the tall back window” Close: silence … silent “The silence in the workshop” Distinctive, chapters apart: meticulous “His records were meticulous” Close: neatly … neat “neatly labeled” Distinctive, chapters apart: gleaming “a gleaming pair of shoes” Distinctive, chapters apart: sodden “carrying sodden leaves” Distinctive, chapters apart: brittle “a short, brittle sound” Distinctive, chapters apart: stubbornly “which stuck stubbornly” Close: remembered … memory “her hands remembered” twins are two “the two twins” one shrugs with the shoulders “shrugged his shoulders” the reason … was because “was because he had never paid himself” a sum is a total “The sum total” an agreement is mutual “By mutual agreement” a haven is safe “a safe haven” began is first “the week we first began” join together “wants them to join together” an outcome is final “The final outcome” Grandfather's eyes: grey, then blue “the same gray eyes as her grandfather” Said on Friday: the day after tomorrow is Sunday “On Friday a woman knocked” Tea becomes coffee “poured her a mug of tea” Tomas beside him: two decades, then thirty years “for most of two decades” The bakery: two doors down, then a ten-minute walk “BAKERY TWO DOORS DOWN” Grandmother: Ruth, then Rose “her grandmother, Ruth”