An AI co-writer with your whole project on its desk.

Proselon is a writing app whose AI co-writer lives inside your project — reading any page on demand, drafting inside the page, and keeping your work consistent. Works with your existing AI subscriptions, no API keys necessary.

Start 30 days freeAlready have an account? Download the app

Do an afternoon of work with one instruction.

The co-writer writes on your own computer in your own project folder. It opens whichever pages it needs and writes back into them directly, so an afternoon of renaming, rearranging, or realigning becomes one instruction.

Perfect attribution, down to the letter.

Proselon keeps a record of who wrote each character of your work, recorded by watching rather than by guessing. When a reader, publisher, or a registrar asks what you contributed, you have an exact answer.

Not every touch is a claim

Only a change to the expression counts. Adding emphasis does not claim a passage, retyping is not composing, and a run of a dozen surviving characters retains its original provenance. A word split evenly never counts as yours, so the metrics err against overstating your share. The rest is in how Proselon attributes authorship.

S1 - At the Board, Mid-Delivery1,530 words

He laughed at me. That was what came up, in the quiet the cold board left me, and not a thing I went and fetched. The lamps along the top row went on blinking as they had all night, each one waiting its turn to be answered. It was there ahead of me, the way a name sits on your tongue before you have gone looking for it.

Saved
Human66%AI34%

It writes like you, not like a chatbot.

AI is much better at reproducing patterns than it is inventing something from scratch, so the Proselon AI co-writer builds a record of passages written in your own voice and uses that as the basis for everything it generates.

A chatbot writes itNO EXAMPLE TO FOLLOW

In that moment, Nora couldn’t help but feel a profound sense of purpose wash over her. The lighthouse stood as a testament to her grandfather’s unwavering dedication, a beacon of hope that had guided countless souls home. For forty years he had tended its light, and now it was her turn to carry that torch forward. Little did she know, everything was about to change.

10TELLS FLAGGED, AND COUNTING
Proselon writes itDRAFTING AGAINST YOUR CORPUS

Another person might have been driven mad long ago by the lighthouse beam, but not Nora. For her, the lighthouse was a welcome reminder. Her grandfather had kept its light for forty years. Now it was her turn to do the same.

✓ MATCHED TO YOUR VOICE CORPUS
Define
Three style records are created

A Style Guide sets the rules, a Voice Corpus collects the passages that prove them, and an Anti-Pattern Corpus records what the AI co-writer does when it goes wrong.

Enforce
Every word generated is revised

Every draft passes a voice rewrite measured against your model passages. The agent that does the revision is separate from the agent that drafted.

Hunt
AI tells and bad habits are contained

Tells that keep returning are entered onto your Anti-Pattern Corpus and hunted across the whole manuscript.

Adopts any role you want.

The co-writer does whatever you ask it to, from being a test reader all the way to drafting an entire series. Shift its role anytime by simply asking.

AI you can put away.

Some days the co-writer is the last thing you want. Hide it with one keystroke, hide the file tree after it, and what is left is the page and its margins. The app you write in when you would rather write alone.

Generate a story graph on demand.

Open the story graph, and Proselon reads your project and draws a web of the concepts within. There is no tagging chore and no metadata you have to update. Folders you create appear automatically in the legend.

Themes you can read all day.

Ten beautiful themes to choose from. Choose a theme for everything you write, or give each project its own. Pick a theme you like, or a theme tailored to your platform.

ThemesChoose one

AO3, FanFiction.net, Wattpad, and Royal Road are trademarks of their respective owners. Proselon is not affiliated with or endorsed by them, and these themes only recreate the look of each site’s reader.

Every theme, in both halves
Paper & Terracotta

Warm paper with a burnt-terracotta accent — the Proselon default.

Markdown files, stored on your computer.

Your project's files are stored on your computer, one UTF-8 Markdown file per page, with a block of YAML at the top. That's it. No database, no container, no proprietary format. Take your work and leave whenever you want.

The Midnight ExchangeManuscripts / Book 1 / Act I / Chapter 1COLUMN VIEW

Every version kept, in a backup that goes anywhere.

Autosaves preserve your work, and any save can be read or brought back, one page or all of them, and is kept even if you restore from an older version. Backups are managed using git, a backup system used by developers, which means you can take your backups with you anywhere.

Versions
Done

Decide what's included in context and what's not.

Lock or hide any page or folder. Each mark covers everything nested beneath it, and each is enforced on the file itself rather than by an instruction a model could ignore.

The Midnight ExchangeBINDER

Locked

A locked page or folder is read but never altered — by the co-writer or by your own editor — until you unlock it. Good for published chapters in serial novels, or published blog articles.

Hidden

A hidden page or folder is invisible to Proselon. The co-writer never reads it, no count includes it, no export carries it, and nothing in the story graph has it, though you still open it and write in it whenever you like.

Line-level citations.

When the co-writer refers to specific parts of your project, it can include a citation. Click the citation and the editor opens to those exact lines. Click the citation widget at the top of the screen to copy a citation you can use in your reply to the co-writer.

ProselonThe Midnight Exchange

Powered by your favorite AI engine.

Proselon's co-writer is powered using whatever AI you want, from frontier models to custom local ones to BYOK.

API key

API Key

BILLED PER USE

OllamaLM Studio

Local Models

FREE · TOOL-CALLING

ChatGPT

ChatGPT

ANY PLAN

Gemini

Gemini

AI PRO OR ULTRA

Grok

Grok

PREMIUM+ OR SUPERGROK

Claude

Claude

PRO OR MAX

Only six dollars a month.

One product, with everything included on both plans. The only decision is how often you are billed, and you make it after the trial rather than now. Your AI subscription is billed separately.

Monthly

$6/ month

Billed monthly. Cancel any time, in one click.

Start 30 days free

Annual

$50/ year

Save $22 a year

Two months on the house, or about $4.17 a month.

Start 30 days free

Both plans include

  • The AI co-writer, on all six engines
  • Continuity across a whole book or series
  • Automatic version history
  • Export to Word, EPUB, and more
  • Every theme, in a light half and a dark one
  • No credits or meters

30 days free, no card · we email before the trial ends · cancel in one click · refunds within 30 days of a charge

Full pricing details and billing questions

Your writing room is ready.

A co-writer with your whole book on its desk, and a manuscript that stays a folder of Markdown you own from the first line. Free for 30 days with no card, then $6 a month, running on the Claude or ChatGPT account you already hold or on a model of your own. No API keys necessary.

Start 30 days freeAlready have an account? Download the app