Using Mosaik.

Install

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

The installer isn't signed yet, so the first time you run it Windows SmartScreen shows Windows protected your PC. That is expected for a new, unsigned program. Choose More info, then Run anyway.

To check the file is the one we published, compare its SHA-256 with the one on the Download page. In PowerShell, in your Downloads folder:

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

The installer puts Mosaik in your own user folder, %LOCALAPPDATA%\Programs\Mosaik, for you only, and needs no administrator rights. It adds Mosaik to the Start menu, and to the desktop if you tick the box, and offers to open it when it's done.

Coming from OpenRouter Chat? Mosaik is the same app under a new name. The first time it starts, it copies your chats and settings across and leaves the old folder as it was, and a remembered key moves with them.

Get an OpenRouter key and add credits

Mosaik reaches AI models through OpenRouter, one account for hundreds of models. You use your own key, and OpenRouter bills what you use to you, at its prices. Mosaik never sees your payments.

1. Sign in at openrouter.ai.
2. Open Keys, create a key and copy it. It starts with sk-or-.
3. To use paid models, add credits. Free models work without them, within the daily limits OpenRouter sets for free models.
4. In Mosaik, paste the key into the setup guide, or into Settings › Connection, and press Test connection.

With Remember securely on, the key is kept in the Windows credential store (Credential Manager). With it off, the key is kept only until Mosaik closes. The key is never written to Mosaik's database or log, and is sent only to OpenRouter.

OpenRouter can also give a key a credit limit of its own, which is a good second safety net beside Mosaik's spending limits.

Your first chat

The first time Mosaik opens, a short setup guide asks for your key, a set of models (a preset: Free, Cheap, Balanced or Best) and a monthly spending limit, then shows you around. Everything it sets can be changed later, and Settings › Appearance opens it again.

• Ask. Type in the message box and press Enter. The answer streams in, and a line above it says what the model is doing: reasoning, searching, reading pages.
• Attach. Drop files anywhere on the window, paste them, or use +. Images go with the message; text files are quoted into it.
• Stop. The send button becomes a stop square while the model works; Esc stops it too, and keeps what was written so far.
• Change the model. The model button at the end of the message box changes it for this chat. Settings › Models sets the one every new chat starts with.
• Act on an answer. Point at a message to copy, edit, regenerate, branch or delete it. Branching starts a new chat from that point and leaves the original as it was. Editing one of your messages removes what came after it.
• Find it later. Chats name themselves from their first message, and Ctrl K searches every chat by title and by what was said.

Every answer shows which model answered, the tokens it used and what it cost. The corner of the window shows how full the model's context is and what the conversation has cost so far. Ctrl E exports a chat as Markdown; JSON is in the palette.

Quick-ask

For a side question that shouldn't derail the chat. Select words in any message and an Ask chip appears beside them; click it, or press Ctrl Shift K.

A popover opens beside the passage. The answer knows the conversation around it, but is never added to the chat, so your main thread stays where you left it. You can ask follow-ups in the popover. Esc closes it and forgets the answers; Open as chat keeps the side conversation as a chat of its own.

Styled answers

Answers can use more than plain text where it helps: a highlighted key idea, a callout for a warning, a timeline, key figures, columns, a small chart. Conversation stays plain; a guide or a report you'll keep gets the design of an article.

• How much styling is set in Settings › Chat style: Off, Light, Auto (the default) or Rich. The same page has the text size, spacing and reading width.
• Pictures a model draws open in a small window of their own. Click one to see it large, and save it as a PNG or an SVG from the answer's ⋮ menu.
• Interactive pieces, such as a calculator or a chart, run in a sealed frame that can't reach Mosaik, your files or your other chats. Chat style can turn off their scripts, web fonts and chart libraries.

Tools and web search

The Search button at the left, under the message box, decides when answers use the web:

Search is free and needs no account. The line above the answer shows every search and every page read, and a chip at the end of a paragraph shows which source it rests on. Settings › Web can point Mosaik at your own SearXNG instance, or turn search off.

Exact tools. Models guess at arithmetic, counting letters, dates and unit conversions, so Mosaik gives them tools that compute the answer instead: a calculator, a text counter, a calendar, a unit converter, a random source and a sandboxed Python. They run on your computer, take milliseconds and cost nothing. The answer's work line shows what went in and what came out.

Search and the tools work best with models that can call tools. A model that can't still gets searches, chosen for it, and a Limited web search note shows while it is selected.

Models and spending limits

Presets. Settings › Models offers four sets of models: Free, Cheap, Balanced (the default) and Best. Each picks the newest model your key can use from families Mosaik is tuned for, and shows its price. You can choose a model for each job yourself, and save your choices as a preset of your own. Recommended models has a Test button that checks a model can use Mosaik's tools.

One chat, one model. The model button under the message box changes the model for the open chat. All models opens the full list from OpenRouter, with search, filters (free, tool calling, reasoning) and each model's prices.

Reasoning. For models that can think before answering, the control beside the model picks how much: Auto lets the model decide, or choose Off, Low, Medium or High. It's remembered per model.

Spending. Settings › Spending shows what you spent today and this month, by model and by kind of work, and every recent call. There you can:

• set a daily and a monthly limit (the monthly one is $10 to start with);
• turn paid models off, so only free ones run and nothing is charged.

Every request is checked against the limits before it is sent. You're warned once when 80% of a limit is used, and a request over the limit is refused with the reason and a button to the Spending page. Costs are OpenRouter's own figures where it reports them, and estimates from its prices where it doesn't; OpenRouter's bill is the one that counts.

Settings

Open Settings with Ctrl , or the button at the foot of the sidebar. Changes apply when you save. Settings that change how Mosaik works are folded into an Advanced section on each page, and are fine left alone.

One chat's own settings. Ctrl /, or Chat settings in the message box's … menu, gives the open chat its own model, instructions, temperature and answer length. The message box shows a Custom tag while a chat has its own settings. The prompt library keeps named instructions you can give any chat.

The Settings assistant, at the foot of the Settings list, changes settings for you when you say what you want, such as “make it cheaper”. It lists what it changed, Undo reverses it, and it never sees your key.

Keyboard shortcuts

The palette (Ctrl P) lists every command with its shortcut.

Updating

Mosaik keeps itself up to date. A little after it starts, and every few hours, it asks mosaikchat.com whether there is a newer version, telling it only Mosaik's version and your Windows version. When there is one, it downloads the installer in the background, checks its SHA-256, and installs it when you close Mosaik. To install it straight away, click Restart to update in the sidebar.

Settings › About and updates chooses how:

You can also update by hand: download the newest installer and run it over the old version. Updates keep your chats, settings and key. What changed is in the release notes.

Uninstalling

Open Windows Settings › Apps › Installed apps, find Mosaik, and choose Uninstall.

Uninstalling removes the program and leaves your data, so reinstalling picks up where you left off. To remove that too:

• Chats and settings are in %APPDATA%\Mosaik\Mosaik. Paste that into File Explorer's address bar, and delete the folder.
• A remembered key is in the Windows credential store. Turn off Remember securely in Settings › Connection before you uninstall, or remove the Mosaik entry under Windows Credentials in Credential Manager. You can also delete the key at OpenRouter.

Troubleshooting

Windows says “Windows protected your PC”

The installer isn't signed yet. Choose More info, then Run anyway. If you'd like to check the file first, compare its SHA-256 with the Download page's, as in Install. If your organisation's policy blocks unsigned programs, there is no Run anyway; ask whoever manages your computer.

The key doesn't work

• Press Test connection in Settings › Connection. It says what OpenRouter answered.
• Check you copied the whole key, starting sk-or-, with no space at either end.
• On OpenRouter's Keys page, check the key is still there and enabled, and hasn't reached a credit limit of its own. If in doubt, create a new key and paste that.

No models, or the model list is empty

The list of models comes from OpenRouter when Mosaik starts. If it couldn't be fetched, the New Chat page says so and offers to try again. Check your internet connection, and that a VPN, proxy or firewall isn't blocking openrouter.ai. Refresh models in the palette (Ctrl P) fetches it again.

Out of credits, or a limit reached

• OpenRouter's credits: the answer shows an error card with OpenRouter's own message. Add credits, or switch to a free model (or the Free preset), then regenerate the answer with Ctrl R.
• Mosaik's own limit: the message says which limit was reached, with a button to the Spending page. Raise it there, or wait for the day or month to turn.

The window flickers or draws strangely

In Settings › Appearance › Advanced, set Drawing to OpenGL, or Software if that doesn't help, and restart Mosaik.

Where the log file is

Mosaik writes what it does, and any errors, to mosaik.log in its data folder, %APPDATA%\Mosaik\Mosaik. Paste that into File Explorer's address bar to open it. The log never holds your API key.

Report a problem

Choose Report a problem in the palette (Ctrl P) or in Settings › About and updates. Say what happened, add your email if you'd like a reply, and leave Include the end of Mosaik's log on if it may help. Keys, tokens and your user folder's name are taken out of the log first, and your chats are never included. You see exactly what will be sent, and nothing is sent until you press Send. Once it's sent, Mosaik shows the report's reference, like MR-7K3Q9X2A; mention it if you ask about the problem in the community. After an error, or if Mosaik closed unexpectedly, it offers the same report.

Still stuck?

Ask in the community, or open an issue on GitHub with your Mosaik version and the end of the log.