Mosaik
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Getting started.

Install Mosaik, sign in with OpenRouter, and ask your first question. The guides cover everything else.

Install

Mosaik runs on 64-bit Windows 10 and 11. Get the installer from the Download page and open it.

The installer isn't code-signed yet, so the first time you run it Windows SmartScreen says Windows protected your PC. Click More info, then Run anyway.

If you'd like to check the file first, compare its SHA-256 with the one on the Download page. In PowerShell, in your Downloads folder:

Get-FileHash .\Mosaik-Setup-*.exe

Mosaik installs for you alone, in %LOCALAPPDATA%\Programs\Mosaik, with no administrator prompt. It adds itself to the Start menu (and the desktop, if you tick the box) and offers to start when it's done.

Connect OpenRouter

Mosaik reaches models through OpenRouter, a single account for hundreds of models from OpenAI, Anthropic, Google, Meta, DeepSeek and others. Mosaik isn't part of OpenRouter or affiliated with it. OpenRouter bills you directly at its prices, and we never see your payments.

  1. In the setup guide, click Sign in with OpenRouter. Your browser opens OpenRouter.
  2. Sign in, or make a free account. OpenRouter shows mosaikchat.com asking for access: that's Mosaik. Click Authorize.
  3. The tab goes back to Mosaik and says you're connected. Go back to Mosaik: it's already moved on to choosing your models.

There's nothing to copy. Mosaik gets a key of its own, called Mosaik on your OpenRouter Keys page, and keeps it in Windows Credential Manager. Later, the same button is in Settings › OpenRouter, with Sign out once you're signed in.

Skipped the setup guide? The New Chat page has a small Connect AI button with the same three choices.

The setup guide's Connect OpenRouter step, with the Sign in with OpenRouter button, dark theme The setup guide's Connect OpenRouter step, with the Sign in with OpenRouter button, light theme

Free or paid

  • You don't have to pay anything. An OpenRouter account is free, and free models need no card.
  • Buy $10 of credit once and OpenRouter raises free models from 50 requests a day to 1,000.
  • Free models are sometimes busy, unavailable for a while, or less reliable.
  • Mosaik is tested with, and works best on, frontier paid models. With credit they're very cheap, usually a cent or two a reply, and every reply shows what it cost. Add credit on OpenRouter.

Use your own key instead

If you'd rather make the key yourself, for example with its own credit limit, choose Paste a key instead in the guide, or Use your own key in Settings › OpenRouter:

  1. Sign in at openrouter.ai.
  2. Open Keys, create a key and copy it. It starts with sk-or-.
  3. Paste it in and click Test the key. It says whether the key works and how much credit is left.

With Remember it securely on, as it starts, a pasted key goes into Windows Credential Manager too. With it off, Mosaik forgets the key when it closes. Either way, the key is never written to Mosaik's database or log, and it's only ever sent to OpenRouter.

Tip: OpenRouter lets you give any key, the one Mosaik signs in with included, its own credit limit. That makes a good second safety net next to Mosaik's spending limits.

Your first chat

On first launch, a short setup guide connects OpenRouter, lets you choose your models (Smart starts on Free, so nothing is spent until you say so) and a monthly spending limit, then shows you around. You can change all of it later, and Open the setup guide, in Settings › OpenRouter or Appearance, runs it again.

  • Ask. Type in the message box and press Enter. The answer streams in, and the line above it says what the model is doing.
  • Attach. Drop files on the window, paste them, or click +. Images go along with the message, and text files are quoted into it.
  • Stop. While the model works, the send button becomes a stop button. Esc works too, and keeps what was written so far.
  • Switch model. The button at the right end of the message box changes the model for this chat.
  • Find it later. Chats name themselves, and Ctrl K searches all of them.

Each answer shows the model that wrote it, the tokens it used and what it cost. The bottom right corner of the window shows how full the model's context window is and what the chat has cost so far.

Guides

Everything else, one topic at a time.

ChattingThe message box and prompts, attachments, files the model makes, the work line, editing, branching, maths, finding, exporting and importing chats, and quick-ask. Web searchWhen Mosaik searches, how much, where the results come from, and how sources are marked. Exact toolsThe calculator, counter, calendar, unit converter, random picks and the Python sandbox. Styled answersHow answers are laid out, pictures, interactive pieces, and how much styling you get. ModelsSmart and Manual, saved setups, the model picker and browser, reasoning, providers and testing a model. Costs and limitsWhat an answer costs, how Mosaik counts it, and the limits that stop a request. SettingsEvery Settings page, one chat's own settings, the prompt library and changing settings from a chat. Keyboard shortcutsEvery shortcut, and the palette that lists them. Updates and your dataHow Mosaik updates, where it keeps your data, backing up, and uninstalling. TroubleshootingFixes for the usual problems, the log, and sending a report.

Something not working?

The Troubleshooting guide covers the SmartScreen warning, keys that don't work, empty model lists, credits and limits, and a window that draws strangely. If that doesn't help, send a report from Mosaik with the speech-bubble button at the top of the sidebar, or ask in the community.