American developer Ben Horwitz has written a Chrome extension called Sinceerly. The service works in the opposite way to popular proofreaders, intentionally adding typos and simplifying language to make emails look like they were written by a human, not a generative AI.
American developer Ben Horwitz has written a Chrome extension called Sinceerly. The service works in the opposite way to popular proofreaders, intentionally adding typos and simplifying language to make emails look like they were written by a human, not a generative AI.
«I created the ‘anti-Grammarly.’ Use AI to ruin your emails,» Horwitz told X on Twitter. He added that he tested Sinceerly by sending unsolicited emails to five Fortune 500 CEOs. Four of them responded.
«Each of these responses contained less than 10 words. Two responses had spelling errors. One CEO called me Larry (my name is Ben)…», the developer Sincerely said.
As Business Insider reports, the emergence of such a tool is due to a change in the perception of perfectly literate texts. If previously impeccable punctuation was considered a sign of intelligence, then in 2026 it is increasingly becoming a marker of «lazy» use of ChatGPT or Claude. Instead, errors in the text become confirmation that the author wrote the message himself.
I made the anti-Grammarly. Mess up your emails with AI. https://t.co/R6kdTpoc0W pic.twitter.com/1AF5qrCFwT
— Ben Horwitz (@horwitzben) April 23, 2026
Sinceerly offers users three text processing modes:
Subtle — removes unnecessary words and adds abbreviations;
Human — gives the text a conversational character and usually makes a mistake in the first sentence;
CEO is the most radical mode, where the text is written only in lowercase letters, becomes as concise as possible, and may contain a signature «sent from my iPhone» to simulate the manager’s busyness.
«I’m a terrible typist and have mild dyslexia. At my first job, I spent a lot of time proofreading emails. When Grammarly came along, I was thrilled, but now my inbox is filled with AI-generated clutter,» explains Ben Horwitz, explaining his motivation.
The developer, who is finishing his studies at Harvard Business School, created the plugin with the help of Claude. Sinceerly is currently available as a Chrome extension. After a few free trials, users are asked to pay $4.99 for further use.
Recall that in March, the Grammarly text writing assistant received support for grammar and spelling in 17 more languages, including Ukrainian.
