MerMark Editor v0.2.0 - Markdown/Mermaid editor with built-in Claude/Codex

Vespi — Tue, 05 May 2026 23:48:33 +0000

Hey, me again. Posted MerMark Editor here a while back — first
post got 120+ GitHub stars and the binaries crossed 7 000
downloads, so thanks to everyone who tried it. Just shipped
v0.2.0 and the diff is big enough that I think it's worth a
fresh post.

Pre-emptive disclaimer (so I don't have to argue in the comments)

Yes, I know Obsidian exists. Yes, Obsidian has AI plugins.
No, I'm not trying to compete with it.

If you live inside a vault with a graph view, daily notes, dataview
queries, six community plugins and a sync subscription, MerMark is
not going to replace that workflow. Don't try to make it.

What MerMark is: a stupid-simple editor that opens .md files
without setup, renders Mermaid diagrams inline, and now talks to
your local Claude Code or Codex CLI when you want help editing.
That's it. Closer to Typora + a chat panel than to Obsidian.

What you still get (baseline carried over from v0.1.x)

Editing

WYSIWYG Markdown — formatted text as you type, not raw syntax
Code view — toggle to raw Markdown with cursor position tracked across both views (Ctrl+Shift+V)
Split view — edit two documents side by side, draggable divider
Syntax highlighting in code blocks, 50+ languages
Tables, task lists, blockquotes, footnotes, page breaks
Character and word count, auto-save, undo/redo

Mermaid diagrams (the "Mer" in MerMark)

Renders inline as you type
Flowcharts, sequence, class, state, ER, Gantt, pie, C4, journey, gitgraph, mindmap, timeline, quadrant, requirement, block, treemap, xy-chart, architecture
Zoom controls + fullscreen mode (up to 400 % for detail work)
Resizable code/preview split inside the fullscreen editor
New diagrams default to 25 % scale so they don't overflow
Crisp PDF export (vector, not rasterised)

File handling

File watching with auto-reload on external changes
Conflict detection with merge dialog. If you've made local edits and the file changes underneath you — another app, a git pull, a sync client, or the AI panel writing to disk during a chat turn — MerMark stops, shows you a side-by-side diff of your unsaved changes vs. what landed on disk, and lets you decide per-side which version wins. No silent overwrite either way. Works the same whether the "external" change is your own AI asking the model to rewrite a paragraph or a teammate pushing to a shared folder.
Atomic save — .tmp write + verified rename, no silent overwrites if the file changes mid-save either
Drag & drop .md files into the editor from your file manager
Manual reload from disk (Ctrl+R)
Tab tooltips with full file path on hover; duplicate filenames show parent folder prefix to tell them apart

Tabs and windows

Multiple documents in tabs, Ctrl+W close, Ctrl+Tab cycle, Ctrl+1..9 jump
Multi-window — open as many independent editor windows as you want
Cross-window drag & drop tabs between panes and windows

Compare and track changes

Compare Tabs — diff between left and right pane documents (Ctrl+Shift+C)
Change Tracking — view all additions and deletions since last save (Ctrl+Shift+D)

Themes and zoom

Dark and light app themes
Separate code-block themes — pick the syntax-highlight scheme independently from the app theme. Includes a white variant added in v0.2.0 so light mode doesn't clash.
Editor zoom (Ctrl+Scroll, or toolbar +/−/100 %)
Mermaid preview zoom independent of editor zoom

Token counter

Live estimate for OpenAI (GPT family), Anthropic (Claude family) and Google Gemini — useful before pasting into a chat

Other

Export to PDF with proper formatting
Plain .md files on disk — git diff still works
Keyboard shortcuts modal (Ctrl+/) auto-renders Mac glyphs (⌘ ⇧ ⌥) on macOS
Lightweight (~15 MB), Tauri-based, not Electron
Everything stays local, no cloud, no account, no telemetry
Bilingual UI (was English + Polish; v0.2.0 adds Chinese — see below)

NEW in v0.2.0 — local AI assistant

This is the headline feature and it's worth explaining because
every "AI editor" launches with the same handwave.

The trick: MerMark doesn't have its own model and it doesn't ask
you for an API key. It shells out to whatever claude or codex
CLI you already have logged in. So if you pay for Claude Code Pro
or OpenAI Codex / ChatGPT Plus, the requests go through the
account you're already paying for. No second bill, no token
budget to manage, no proxy in the middle.

What it can actually do:

Edits your markdown directly. "Rewrite this section friendlier", "extract action items", "translate the meeting notes". The AI writes straight to disk; the editor reloads from the file.
Reads across folders you authorize via a per-document access map.
Writes peer files when you let it. Generate a summary alongside the source, split a long doc, build a TOC.
Optional toggles for shell + web search. Both off by default.
Auto-snapshots before every AI write, with a one-click revert.
You and the AI can both be editing the same file. If you type while the AI is mid-write, the conflict dialog from the baseline section kicks in and you pick what to keep — your paragraph, the AI's rewrite, or both. No more "AI just clobbered my changes" surprise.

You can pin highlighted paragraphs from the editor and the model
gets just those, not the whole doc — works in both visual and code
view. Paste screenshots into the chat with Ctrl+V (or drag a file
in). Both Claude and Codex see the image. Sent attachments stay in
the chat history as thumbnails so you remember what you fed it.

Threads are per-document and each one remembers the CLI / model /
effort you were using. Reopen an old chat and the panel snaps back
to whatever provider/model you had set.

Every tool call (file read, file write, bash, web fetch, codex
shell, ...) shows up inline in the transcript as an expandable
chip with the full JSON args. If a model runs a shell command,
you see exactly which one.

Bonus — ask the AI to write Mermaid for you.** Paste "draw a
sequence diagram of the OAuth flow we just discussed", let the
model write the


 block, watch it render inline. Beats
hand-tweaking syntax until the arrows line up.

## NEW in v0.2.0 — UI / Layout

- **Configurable layout.** Drag toolbar items between top toolbar,
  bottom status bar, left sidebar, or hide them entirely.
  Settings → Layout. Persists across restarts. Some items have
  constraints (Statistics doesn't fit in the narrow sidebar —
  won't let you drop it there).
- **Expandable left sidebar.** Toggle the chevron to widen it
  from a 40 px icon strip to a 168 px column with text labels.
  Like VS Code's activity bar.
- **Custom fonts.** System font picker for the editor and a
  separate one for code blocks. Live preview of every font.
  Adjustable line height.
- **Trilingual UI** — English, Polish, Simplified Chinese.
- **Page breaks** — `---` actually renders as a page break in PDF
  export now, not a horizontal rule.
- **Table of Contents sidebar** with click-to-navigate
  (Ctrl+Shift+T).

## NEW in v0.2.0 — bug fixes worth calling out

- Cursor mapping across Code ↔ Visual now uses a source-line block
  parser instead of DOM estimation; survives large code blocks and
  font-size changes
- Code-view tab switching no longer loses content
- Trailing blank lines no longer appended on save
- Mermaid fullscreen renders at 1:1 instead of inheriting document
  zoom
- macOS file-open handler from #66 ported in
- Resilient line numbers when content height changes mid-stream
- White theme option for Code view so syntax highlighting plays
  nice with light mode (#67)

## Links

- GitHub: https://github.com/Vesperino/MerMarkEditor (120+ ⭐, 7 000+ downloads)
- Download: https://github.com/Vesperino/MerMarkEditor/releases
- Release notes for v0.2.0 with all the screenshots:
  https://github.com/Vesperino/MerMarkEditor/blob/master/RELEASE_NOTES.md

Windows, macOS, Linux. Free, MIT, completely local.

If you find a bug, open an issue. If you have an opinion about
Obsidian, please go post it under one of the eight Obsidian
threads on the front page of /r/ObsidianMD instead of mine,
appreciated.

DEV Community: Vespi

MerMark Editor v0.2.0 - Markdown/Mermaid editor with built-in Claude/Codex

Pre-emptive disclaimer (so I don't have to argue in the comments)

What you still get (baseline carried over from v0.1.x)

NEW in v0.2.0 — local AI assistant