Mikan-chan, a girl with orange hair in an indigo polka-dot jacket, tucked under a kotatsu at night with a laptop, a bowl of mikans and snow outside the window

The warm table you don’t want to leave.

Kotatsu is SillyTavern for writing. Your characters, presets and extensions, behind a calm, fast interface, with Mikan-chan to set it up alongside you. It's free, open source, and runs on your own computer or phone.

Download for Windows Get the Android app Mac or Linux? Run it from source

Version 0.8.0. Edge will ask whether to keep a .bat file. That's normal for an installer like this one; choose Keep.

See it in a minute

The stage on your desk, the whole cast, every face from one drawing, story lines that branch, and the phone version to take with you. Mikan-chan does the introductions.

On your phone, it's a visual novel

Turn on sprites and the phone becomes a stage: the chat's own backdrop, the speaker in the face that fits the line, and the reply in a textbox you tap through a page at a time. Tap their name for the details. History brings the whole transcript back.

Rin in a sunlit bookshop, holding a book, with her reply in a textbox at the bottom of the screen and a small arrow saying there is more
One line at a time, a page at a time
A scene in a rainy café: Mara the pirate captain on stage, the cast of three in a row under her line
Scenes: whoever speaks steps forward
The History view: the bookshop scene dimmed behind the whole conversation
History, when you want the whole story

Everything SillyTavern let you shape, made cozy

Same characters, presets, extensions and data folder. A calmer page around them.

Mikan-chan at a little chalkboard, pointing with chalk

A guide who sets it up with you

Mikan-chan walks you from hello to your first message in five steps: connect a model, pick a preset, say who you are, choose a character, and start writing. Skip any step, or the whole tour, and replay it later from Settings.

“First time? Perfect. I'll walk you from hello to your first message. Skip anything you like; I'll only sulk a little.”

Mikan-chan holding up a chunky power plug

Use the subscription you already have

  • Claude Code with your Claude plan, or your ChatGPT Plus or Pro plan. No API key to manage.
  • An API key from Anthropic, OpenAI, Google AI Studio, DeepSeek, xAI or OpenRouter. Keys stay on your computer.
  • A local model, NanoGPT, Mistral or any custom endpoint.
Mikan-chan taste-testing a little pot with a wooden ladle

Presets you can actually read

The prompt list comes in sections, toggles say what they do, and every reply keeps a receipt of the exact prompt the model saw. Your own presets load unchanged.

Kotatsu Nabe is the house preset. Sola, Freaky Frankenstein and Nemo Vivarium ship beside it, with their authors' permission and credit.

Mikan-chan holding up a phone that shows a little visual-novel stage

It comes with you

Scan one QR code and your phone joins in, at home on your Wi-Fi or anywhere on your tailnet. Same chats, same characters, same connections. On a phone the story takes the whole screen, and with sprites on, your cast stands on a little visual-novel stage above it.

“Yes, I fit in your pocket too.”

Mikan-chan winking with a paint palette and a brush, a dab of orange on her cheek

Make it look like yours

Natsumikan leads six themes in the box, with Natsumikan Classic and Manga, Blue Hour, Sparkle and Midnight Kissaten beside her. Pick a message style, from bubbles to script to broadcast, or put your cast on stage with sprites you bring or Kotatsu draws for you.

Try two of them on this page:

Look closer

The Card Studio's Looks chapter: a character's sprite and her faces side by side, neutral, joy and more

Every face, from one drawing

The Card Studio keeps a character's whole look in one place: card art, a full-body sprite, a bust, and every expression big enough to judge.

The sprite generator showing four drawings of Juno, a pink-haired netrunner, each marked clean, waiting for one to be picked

Kotatsu draws the set

Pick the drawing you like and Kotatsu paints every expression from it, cut out and ready for the stage. Your own ComfyUI does the drawing.

A noir chat with Sable the detective, and a picture of her at a rain-streaked window drawn into the conversation

Pictures of the story

Draw this moment, a character, yourself or the place. Kotatsu writes the prompt from the scene, you can edit it, and the picture lands in the chat. Also on your own ComfyUI.

Story lines: one story drawn as a transit map, the main line with two branches forking off at different messages

Every branch, on one map

Fork any message and keep both endings. Story lines draws a whole story as a transit map, so you can always find the way back.

A prompt receipt: 2,415 tokens split into chat history, preset and character, with a bar for every part of the preset

See what you sent

Every reply keeps a receipt of the exact prompt the model saw, by source and in order, and every reply shows its tokens and cache hits.

Settings, Phone: an iPhone has just paired, and Mikan-chan is cheering about it

Your phone, in one scan

Turn on phone access, scan the code, done. Only phones you pair can connect, and the code works once.

A look around

Mikan-chan's welcome tour, every step skippable
Mikan-chan walks you through setup
The Connect step with Claude Code in use through a Claude subscription, and ChatGPT one click away
Use the subscription you already have
The cast library under the heading Who are we meeting tonight?, a shelf of character posters
Your cast, on one shelf
The reader: a noir chat with Sable, the characters and chats on the left, the preset's sections on the right
A reader made for long stories
A scene called Closing Time: Kaito, Mara and Rin in one chat, with the On stage strip under it
Scenes: more than two at the table
The same scene in the Sprite look on a computer: Rin and Kaito on the left, Mara on the right, over the café backdrop
The stage on a big screen
Mikan-chan hugging a big soft cushion shaped like a download arrow

Get Kotatsu

You don't need a Claude subscription. An API key, a ChatGPT plan or a local model works just as well.

Download for Windows
  1. Double-click Install-Kotatsu.bat. It installs Node.js and git if they're missing. No admin rights needed.
  2. It asks whether you want to use a Claude Pro or Max plan. Say yes to set up Claude Code, or no to skip it. Either way the install finishes.
  3. Kotatsu opens in your browser, with Mikan-chan waiting. A shortcut lands on your Desktop.

On Android (9 or newer): download the app on your phone and open it; allow installs from your browser when Android asks. Everything runs on the phone. Connect it with an API key or a model on your network; Claude Code and ChatGPT plans need a computer.

On macOS or Linux, run it from source. Coming from SillyTavern? Copy your data folder in and everything carries over.