The review loop

Review what the agent wrote. Hand back a brief it can act on.

Show Changes marks what changed in the rendered view, anchored notes pin your comments to exact source ranges, and Copy Report folds notes and diagnostics into one line-anchored brief.

The short version

A coding agent writes documentation faster than you can read it. Twain is the review surface in between: a rendered diff shows what actually changed against the last save, a chosen revision or git HEAD; anchored notes attach change requests to exact ranges of source; local version history answers "what did it just do?" in any folder, git or not; and one action turns all of it into a brief the agent can execute. Show Changes and diagnostics are free, including the one-click diff when an agent rewrites the file you have open. Version history, notes and the agent brief are Pro.

The five review tools

Each one exists because agent-written documents changed how review works.

rendered diff

Show Changes Free

Added, changed and moved blocks are marked in the rendered preview and removed blocks appear inline, against the last save, git HEAD or any local revision. Re-render noise from highlighting, maths and Mermaid never counts as a change.

pin a note

Anchored review annotations Pro

Attach a note, change request or question to an exact range of source. Notes re-anchor as the text shifts, mark themselves orphaned when the quoted text is gone, and live in a sidecar beside the file, never inside it.

to your agent

Copy Report for Agent Pro

One action folds your notes and the document's diagnostics into a patch-oriented, line-anchored brief: change requests, then questions, then notes.

local history

Version history for any file Pro

Every document keeps a private, deduplicated history of its own versions, captured only when content changes and never on a read. Browse them side by side and restore any revision as an unsaved edit that is itself reversible.

diagnostics

Document diagnostics panel Free

A status-bar badge surfaces imports, expressions, unknown components, missing images and broken links, each with its source line.

proofing

Spell, grammar and style checks

Native continuous spell-check and grammar toggles that never rewrite your Markdown, plus a light style check that flags weasel words, filler and duplicated words as non-destructive underlines.

Show Changes · since last save

12 ## Installation
13 Run the setup wizard.
13 Run `npm install` then `npm start`.
14 ## Configuration
15 Set the API key in .env first.
   @@ note → confirm the env var name with the API docs
     ▸ 2 blocks added · 1 changed · 1 note

Built around the loop, not bolted on

The agent ships a folder of docs. You press space or open the folder. Show Changes tells you what moved since you last looked. You pin notes to the lines that need work. Copy Report hands back one structured brief, and live refresh shows the fixes landing as the agent writes them. Every step is designed to feed the next.

History without a repo

Agents love rewriting files in place, and not every docs folder is a git repo. Local version history gives every document a private record of its own past versions: captured only when content actually changes, deduplicated, pruned by age and size, and restorable as an unsaved change. Versions are captured whether or not you have Pro, so an overwrite stays recoverable and nothing is missing if you unlock later; browsing and restoring them is Pro. When an agent rewrites the file you have open, the free viewer still offers you the diff against what it was, in one click.

On the phone too, soon

An iPhone and iPad review companion is in development and heading to TestFlight: the same renderer, the same anchored notes, round-tripping with the Mac through the same sidecar file. There is no App Store listing yet, and this site will say so the day that changes.

Questions

Do I need git for the diff or the history?

No. Show Changes diffs against the last save or any local revision out of the box, and adds git HEAD as a baseline when the file lives in a repo. Version history works in any folder.

Where do review notes live?

In a hidden JSON sidecar beside the document, never inside the file itself. The Markdown you hand on is byte-for-byte what you reviewed.

What goes into the agent report?

Your anchored notes, re-anchored against the current source, plus the document's own diagnostics (unknown components, imports, missing images, broken links), all with line numbers, ordered as change requests, then questions, then notes.

Which parts of the review loop are free?

Show Changes and the diagnostics panel are free, including the one-click diff when something rewrites the file you have open. Anchored notes, Copy Report for Agent, and browsing or restoring version history are Pro, a one-time purchase with a 7-day trial built into the app.

This page describes what the app does today; when a capability is partial or pending, it says so. See how Twain compares to other Mac Markdown apps.

More capabilities

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