Why 
andem
Most writing tools hand you a blank page and wish you luck.
Tandem hands you a blank page and a co-author who is actually reading along.
A Markdown editor where you and Claude share one file. Highlight a line and Claude can read it, mark it up, and suggest a change — right in the margin.
How it works
A second pair of eyes, without the back-and-forth
The whole loop happens in one window. No tab-switching, no copy-paste, no losing your place.
Highlight a line
Select the sentence you're unsure about. Claude sees exactly what you see.
Claude leaves a note
A comment, a suggestion, a flag — in the margin, tied to that line.
Keep it or skip it
Accept the change as a diff, or dismiss it. You decide every time.
What's inside
Everything happens on the page
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 quiet
Pause Claude to write alone. Anything it queued up is waiting in the margin when you switch back to Tandem.
Your files, your machine
Opens the Markdown, text, HTML, and Word files already on your disk. Local-first — nothing moves unless you say so.
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.
In Solo, Claude steps back and holds its notes. The margin shows 3 held until you’re ready.
Solo & Tandem
Quiet when you need it, company when you don’t
Some drafts want a collaborator. Some want silence. Flip to Solo and Claude pauses — no interruptions, no notes appearing mid-sentence. Switch back to Tandem and everything it set aside is waiting for you.
Who it's for
If you write it down, Tandem helps
It's a plain Markdown editor first. The co-author is there when you want one.
Essays & articles
Draft long-form and get a line editor who works in the margin, not over your shoulder.
Studying & notes
Turn reading into notes, then ask for the gaps, the counterpoints, and the plain-English version.
Docs & READMEs
Keep technical writing honest. Flag the steps that don't quite work and tighten the rest.
Reports & memos
Cut the padding. Claude suggests shorter, you decide what survives.
Open a file and try writing together
Free to download. Works on the files you already have. No account needed to start.