Features
Less ferrying text around.
More writing.
Tandem keeps the conversation with Claude on the page instead of in another window. Here’s what that looks like.
The case for the long walk
Most of the good ideas I’ve had arrived on foot. Not at a desk, not in a meeting, but somewhere around the third mile, when the city stops asking for my attention and starts handing some of it back.
There is a kind of thinking that only happens when you are moving slowly enough to notice things but a little too fast to stop and write them all down. So I keep walking, and I keep a small notebook for the ideas that survive the trip home.
The trick is to leave before you know what you are looking for. A route with too clear a destination is just a commute.
Shared selection
Highlight, and Claude already knows
When you select text, Tandem hands that exact passage to Claude over MCP. You don't paste it into a chat or describe where it lives — the selection is the message.
- No copy-paste between windows
- Claude reads the same words you see
- Works on a word, a line, or the whole file
Annotations
Four ways to mark up a page
Claude and you both work in the margin. Comments start a thread, suggestions arrive as diffs you can accept, flags raise a question, and highlights mark what should stay.
- Suggestions apply with one click
- Flags and comments keep a record
- Filter the rail by type or author
Solo & Tandem
Comment now, share when you're ready
Tandem mode is live collaboration: Claude sees your comments as you leave them. Solo holds your comments and replies back until you switch, so you can mark up a draft without Claude reacting to each one. Chat and edits carry on as usual.
- One toggle in the title bar
- Held comments reach Claude together when you switch back
- Chat still works in Solo
Files & privacy
It opens the files you already have
Markdown, plain text, and HTML files all open natively. Tandem is local-first: it reads and writes files on your disk, with no Tandem account, no cloud, no telemetry. Your documents reach an AI only through the Claude you connect.
- .md, .txt, and .html
- HTML opens read-only, for annotating
- Local-first by default
The short list
And the rest of it
Small things that add up to a tool that gets out of your way.
Claude sees what you select
Highlight a line and it goes straight to Claude through MCP. No pasting, no re-explaining which paragraph you meant.
Notes in the margin, not a chat wall
Comments, suggestions, flags, and highlights sit on the document, right next to the line they're about.
Accept changes inline
Every suggestion shows up as a clean diff. Apply the ones you like without leaving the editor or breaking your flow.
Solo when you want to think first
Keep your comments to yourself while you mark up a draft. Switch back and Claude gets them all at once.
Your files, your machine
Opens the Markdown, text, and HTML files already on your disk. Local-first — no Tandem account, no telemetry.
Always know who wrote what
Your edits show in cobalt, Claude's in coral. The two colors run through the whole app so authorship is never a guess.
Open a file and try writing together
Free to download. Works on the files you already have. No account needed to start.