Ben Horowitz, the a16z cofounder whose firm has been one of the loudest financiers of the generative AI buildout, just shipped a browser plugin called Sinceerly that does the opposite of what most AI productivity tools do. Instead of cleaning your writing up, it dirties it down. The plugin inserts typos, drops capitalization at the start of sentences, introduces grammatical mistakes, and optionally appends a "sent from my iPhone" footer. Severity is configurable: Subtle, standard, or CEO mode, the last a wink at how famously casual top executives' emails read in actual practice. Horowitz pitched it himself with the line "I made the anti-Grammarly. Mess up your emails with AI." He says cold-emailing Fortune 500 CEOs through Sinceerly yielded an 80% response rate, with replies that themselves contained natural imperfections.

There is something useful sitting underneath the joke. Two years ago the social signal of a polished email was professionalism; today it is increasingly the signal that you did not write it. Recipients have learned to read em-dashes, perfectly balanced sentences, and the word "delve" as evidence of LLM ghostwriting and to discount the message accordingly. Horowitz's bet is that the equilibrium has flipped: friction in the prose is now what marks an email as worth opening. That insight is correct, even if the product implementing it is gimmicky. The deeper move — and the part nobody is publishing tools for yet — is the labor people now perform to make AI-assisted output read as if it weren't, which is its own kind of authenticity tax.

The implementation is also a small case study in how brittle these consumer-grade plugins are. Coverage of Sinceerly drove a wave of users to the site, and the plugin reportedly broke under the load almost immediately, leaving it "largely useless" for new signups. That is the stuff every consumer launch gets wrong, and it is more revealing than the product itself. If you ship a tool built on top of LLM API calls and ride a press cycle into traffic ten or fifty times your baseline, you find out fast whether your error handling, retry logic, and quota management are real. Sinceerly's outage is not unique; it is the default outcome for most plugins-as-side-projects. The professional version of this category is going to get built, and it will not be by VC podcasters.

For builders, Sinceerly is mostly interesting as evidence that the cultural reception of LLM output is shifting in real time. The signaling value of polished writing is decaying, the signaling value of perceived effort and human texture is rising, and there is now a market for tools that synthesize the latter on demand. That is a slightly cursed market — selling fake imperfection to make AI output land — but it is a market. Expect copycats with better engineering, expect platforms like Gmail and Outlook to add native "make this less polished" toggles within a year, and expect the same arms race to play out in detection: tools that read for the texture of inserted typos and flag them as artificial in their own way. The aesthetics of authenticity are now an engineering problem.