FlatWrite

Write once, style many worlds.

Markdown is one of the greatest cross-platform information formats ever invented. Ironically, while it is easy to read, it is also somehow difficult to read.

FlatWrite makes it easy — and actually pleasant — to work with markdown files. It renders your markdown in the most pleasing, customisable viewing format. From there, it is one quick step to becoming the markdown editor you reach for by default. And once the file looks and reads the way you love it, export it as HTML or PDF, or send it around as a shareable URL.

What it does

• Load markdown from a URL, a file on disk, or by dropping a file (PDF, PPTX, DOCX, XLSX, CSV, JSON, images, audio) — non-text files are converted to Markdown by the MarkItDown extract service.
• Import from URL — paste any webpage URL and FlatWrite converts it to Markdown via Cloudflare's markdown.new service, then loads it straight into the editor.
• Edit markdown with a clean, minimal editor and a helpful formatting toolbar.
• View your rendered markdown with a clean, document-first preview.
• Read mode gives you a focused, distraction-free preview you can resize to taste.
• Export to .md, .html, or .pdf whenever you are ready.
• Share your document as a real URL

Share & publish

The share button is the jewel in the crown. Instead of stuffing a long document into a URL hash, FlatWrite saves the markdown to a paste bin backend and returns a short, readable link. The recipient can open the link and immediately see the document in the same preview style you chose.

• Links are short enough to paste into a chat, email, or a tweet.
• The document is stored server-side, so it works with large files and survives URL-length limits.
• Opening a shared link loads the exact content, ready to read, edit, or re-export.

Typography and layout

The preview is built around a polished document experience with fine-grained controls:

• Eight bundled fonts to choose from:

  • Inter (variable, 100–900) — the workhorse
  • JetBrains Mono (variable, 100–800) — for code-heavy docs
  • Lora (variable, 400–700) — a contemporary serif
  • Merriweather (variable, 400–900) — a reading serif
  • Playfair Display (variable, 400–900) — a high-contrast display serif
  • Comfortaa (variable, 300–700) — a friendly geometric
  • Lato (300 / 400 / 700) — a humanist sans
  • Unbounded (variable, 200–900) — an expressive display sans

• Pick a font, then tune size, weight, and line spacing until the reading rhythm feels right. Adjust UI zoom when the chrome needs to be a little larger or smaller. All fonts are self-hosted and bundled, so the rendered output has no external font dependency.

PDF-only vertical spacing

FlatWrite supports a proprietary self-closing tag for adding controlled blank space to paged output:

<fw-break lines="3" />

lines inserts that many line-heights in Paged.js and Vivliostyle output. Values are truncated to integers and clamped to 0–24; omitted lines defaults to 1, while invalid values insert no space. The tag is removed entirely in Plain and Read modes, so it never appears as visible text.

Choosing a pagination engine

FlatWrite offers three rendering modes, selectable from the Engine section of the sidebar. Hover over an engine button to see its feature summary.

Engine	Best for	Tables	Running headers	Page counters	Startup
Plain CSS	Quick edits, WYSIWYG preview	N/A (no pagination)	N/A	N/A	Instant
Paged.js	Text-heavy documents, fast turnaround	Basic (may break mid-row)	Unreliable across page breaks	Accurate in preview	Fast (~70KB)
Vivliostyle	Books, complex layouts, documents with tables	Full CSS Table support	Reliable via string-set/string()	Always accurate	Slower (~1.2MB)

All three engines share the same typography controls (font, size, weight, line spacing), page size/orientation settings, and <fw-break> support. The choice only affects how the document is paginated for View mode and PDF export.

Quick guide: If your document has tables, chapter headings with running headers, or multi-column layouts, use Vivliostyle. If you just need to paginate a text-heavy document quickly, use Paged.js. Use Plain CSS for editing and quick preview — no pagination, no PDF export.

Get started

Open flatwrite.md in your browser.

Then either paste a markdown file into the text area, open a markdown file that's already on your hard disk, or open one from a URL.

Make any edits to the raw markdown in Edit mode, then switch to View mode to apply style changes, then click on Read to see the final version in an uncluttered layout. When you click on the Share icon, the URL gets automatically copied to your clipboard.

For developers

FlatWrite exposes the same renderer that powers the editor as a public HTTP API and an MCP server. The full specification — tool reference, authentication model, output schemas, and setup examples — is in mcp/MCP.md. FlatWrite exposes the same renderer that powers the editor as a public HTTP API and an MCP server. The full specification — tool reference, authentication model, output schemas, and setup examples — is in mcp/MCP.md.

AI Assist (Morph): rewrite / shorten / fix grammar / custom instructions via Reflex → Router → Compact → Fast Models. See docs/MORPH-ASSIST.md. Endpoint: https://assist.flatwrite.md/assist.

curl -X POST https://render.flatwrite.md/render \
  -H 'Content-Type: application/json' \
  -H 'X-Api-Key: ***' \
  -d '{"markdown":"# Hello, FlatWrite"}'

A second endpoint, https://extract.flatwrite.md/extract, accepts multipart/form-data uploads and converts non-text files to Markdown via the MarkItDown service under services/extract/. The proxy Worker under workers/flatwrite-extract/ mirrors the auth model of the render Worker.

Import from URL: POST /api/import-url (canonical handler: api/import-url.js) accepts { url, method?, retain_images? } and forwards the request to Cloudflare's markdown.new service, which converts an arbitrary webpage into Markdown.

• method selects the conversion pipeline: auto (default — tries the fast path, falls back automatically), ai (LLM-assisted extraction), or browser (renders the page in a headless browser first — slower, but the only option that reliably works on JS-heavy/SPA sites).
• retain_images (default: true) controls whether image references are kept in the returned Markdown. FlatWrite's viewer/export pipeline (core/render.js, core/inline-assets.js) already resolves and renders images from markdown, so keeping images on by default preserves the most faithful reading experience; turn it off for a text-only import.
• The endpoint validates the target URL (http/https only, no localhost, no private/reserved-network addresses, with a DNS-rebinding guard), enforces a request timeout, and never forwards raw upstream error bodies to the client.
• The frontend's existing Load from URL dialog (sidebar → From URL) gained an "Import as a webpage" checkbox with an Advanced options section for method/retain_images. On success the returned Markdown replaces the editor content through the same setEditorContent() path used by every other load flow — there is no parallel document model. If the import looks unusually thin (likely a JS-heavy site that auto couldn't handle), FlatWrite surfaces a "Retry with browser mode" button.
• Limitations: authenticated/paywalled pages and highly dynamic content may still convert poorly even in browser mode, since markdown.new cannot authenticate on the user's behalf. This feature requires the backend endpoint to be reachable (Vercel deployment or the local index.js/dev server) — it does not work against a static-assets-only deployment.

The OpenAPI spec is in openapi.yaml.

Why another markdown editor?

Because most editors either look like a code playground or a publishing pipeline. FlatWrite sits somewhere sweeter: close enough to the raw text that you still control it, but polished enough that you actually enjoy reading and sharing what you create.

License & Commercial Use

flatwrite.md is dual-licensed to accommodate both open-source community use and commercial product integration.

1. Open Source (GNU AGPL v3.0)

For open-source projects, community developers, and non-commercial setups, this software is licensed under the GNU Affero General Public License v3.0.

Under this license, if you modify flatwrite.md or embed it into a web application served over a network, you must make your entire application's source code publicly available under the same AGPL v3.0 terms. See the LICENSE file for details.

2. Commercial Licensing (Enterprise & SaaS)

If you are a SaaS startup wanting to embed this editor into a closed-source proprietary platform, or a company hosting it internally without disclosing your infrastructure code, the AGPL v3.0 terms will not work for you.

We offer a Commercial License Exemption that allows you to:

• Embed the editor directly into commercial, proprietary SaaS products.
• Run the tool on private corporate networks and intranets.
• Keep all your proprietary wrapper, backend, and platform code completely private.

Get in touch with Mahesh Shantaram.