Comment on a document. Talk each comment through with an AI agent.
Let it make the change — and keep only what you approve.

REX

Review EX — third in the family after VEX and DEX.

Why REX

Reviewing a document with AI still means copy and paste. You copy a paragraph into a chat, explain where it came from, and carry the answer back by hand. The chat does not know where that paragraph lives. And when you finally let an agent edit the file, it changes more than you asked.

REX puts the conversation on the document. Select a sentence, a table cell, a region of a chart or a whole section, and write a comment. An agent answers that comment, with the document open in front of it. When you agree on what should change, switch the same box from ASK to ACT. The agent edits a copy, REX shows you the change, and your file stays untouched until you press Approve.

• The place is never lost. Comments stay attached while the document is edited, and a comment whose passage is gone says so instead of jumping to the wrong paragraph.
• One comment, one conversation. Every comment is its own thread with its own agent session.
• A question cannot change your file. ASK runs every agent read-only, and REX checks each tool call before it runs.
• Your agent, your model. Claude Agent SDK, Codex, OpenCode or Deep Agents — on a subscription, an API key, or a local model in LM Studio or Ollama.
• Nothing hidden. Traffic shows every request sent to a model and every answer, down to the JSON.

Install

System	Status
macOS on Apple silicon	Supported — macOS 12 or newer
macOS on Intel, Windows, Linux	Not supported

1. Download REX-<version>-arm64.dmg from the latest release.

2. Open it and drag REX into Applications.

3. The build is not signed yet, so macOS says REX "is damaged" or "cannot be verified". Clear the download flag once, then open REX:

   xattr -dr com.apple.quarantine /Applications/REX.app

Connect a model

You have	Do this
A Claude subscription	Sign in to Claude Code (claude login). The default agent uses that login
A Codex subscription	Sign in to the Codex CLI (codex login), then choose Codex in the comment box
An API key, or a local model	Settings (the cog) → switch on Run the built-in gateway → add Anthropic, OpenAI or OpenRouter with a key, or LM Studio, Ollama or Unsloth with its address

Your first review

1. Open ▾ → Document… or Folder as a workspace…
2. Select text. Press P to pick a table, figure or section instead, or N to circle things with the pen.
3. Write a question and press Ask about 1 (⌘↵). Reply to keep talking.
4. Press ⇧⇥ to switch to ACT, write what should change, and press Change 1.
5. Look at the change, then Approve or Discard.

What REX can do

• Point at anything — text, a table, a row, a cell, a region of a figure, a node in a Mermaid diagram, a section, or the whole document. One comment can hold many places, across many documents.
• ASK, ACT and NOTE — ask an agent, have it make a change you approve, or just leave a note for yourself.
• Four agents — Claude Agent SDK, Codex, OpenCode and Deep Agents, all in both modes. Pick the agent and model per message.
• A built-in gateway — REX's own LiteLLM, on 127.0.0.1 only. Provider keys are stored encrypted with the macOS Keychain.
• Traffic — every chat REX ran, and every request and answer that went through the built-in gateway.
• A folder is a workspace — an explorer with comment counts, a graph of how the documents link, find (⌘F), search (⌘⇧F), and links you can follow and go back from (⌘[ / ⌘]).

Format	ACT can change it
Markdown, HTML	yes
Word (.docx)	through 10 checked operations
PowerPoint (.pptx)	through 13 checked operations
PDF	no — read-only

docs/FORMATS.md explains what REX will and will not do to each format.

Run from source

You need an Apple-silicon Mac, Node.js 22.18 or newer, uv, and the Xcode Command Line Tools.

git clone https://github.com/lukaskellerstein/rex.git && cd rex
npm ci
npm run rebuild                    # better-sqlite3 against Electron
(cd agent-runner && uv sync)
(cd local-gateway && uv sync)
npm run dev

Run npm run rebuild after every npm install — otherwise the app dies on its first database query. Tests are one suite per file: npm run test:<name>. npm run package builds the DMG.

How it works

Four processes. The renderer shows the document and resolves comment anchors on the live page. Main is the only privileged process: it holds the SQLite database at ~/.rex/rex.db, the documents on disk, and the gate that checks every tool call. The agent library (agent-runner/) is a Python child that runs every agent SDK and talks to main over stdin and stdout. The built-in gateway (local-gateway/) is a second Python child, running only while it is switched on.

Contributing

A personal project, with no contribution process yet. The specs in docs/my-specs/ are the authority on what REX is, and .claude/CLAUDE.md is the workflow every change follows.

License

Not licensed for redistribution. No LICENSE file has been chosen yet.