Coda One is a small set of AI writing tools built around one loop: check a draft, then fix what the check finds. It is made for students, teachers, bloggers, content writers and small teams who want to understand how their writing reads before they share it.

The centre of the product is the AI Detector. It is free with no daily limit and no signup, so you can paste a draft and check it straight away in your browser. Instead of only returning a single score, it marks the specific sentences that read as machine-written, which makes it easier to see where a draft feels generic and where it already sounds like you. Detection is evidence, not proof: the result is a starting point for a closer read, not a verdict about who wrote the text. Read the highlighted sentences, decide what to keep, and edit the rest in your own words.

Alongside the detector sit three writing tools. The AI Humanizer helps turn stiff, formulaic passages into clearer, more natural prose, with five free writing modes: Standard, Academic, Blog, Formal and Simple. The AI Rewriter rephrases a sentence or paragraph in one of five free tones: Standard, Fluency, Formal, Casual and Concise. The Grammar Checker catches spelling, grammar and punctuation slips before you publish or hand in your work.

All four tools work in the browser and in a Chrome extension that also runs on Edge, Brave and other Chromium browsers, so you can check and edit text where you already write. The writing tools are free for three runs a day without an account, or five a day with a free account, and no card is needed to sign up.

Coda One is English-only and is built by a small independent team in London. It does not promise to beat or bypass any detector; the goal is simply clearer writing and a better understanding of how a draft reads.