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.

• Load markdown from a URL, a file on disk, or by dropping a file (PDF, DOC/DOCX, PPT/PPTX, XLS/XLSX, CSV, ODT/ODS/ODP, RTF, EPUB, images, audio) — non-text files are converted to Markdown locally by the AnyDoc extract service.
• Import from URL — paste a URL to a document file and FlatWrite fetches it, converts it locally with AnyDoc, and loads the Markdown 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

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.

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.

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.

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

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.

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.

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 locally via the AnyDoc 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? }, fetches the URL, and converts the downloaded document locally with AnyDoc. Only document files are supported; HTML web pages are rejected.

• method is accepted for backward compatibility (auto, ai, browser) but is ignored by AnyDoc.
• retain_images (default: true) is accepted for backward compatibility but is ignored by AnyDoc.
• 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) still sends method/retain_images for backward compatibility. 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.
• Limitations: only document files are supported. Web pages and authenticated/paywalled content cannot be imported because AnyDoc does not convert HTML or authenticate on the user's behalf. This feature requires the backend endpoint and the extract service to be reachable (Vercel deployment or the local index.js/dev server plus services/extract on port 8000) — it does not work against a static-assets-only deployment.

The OpenAPI spec is in openapi.yaml.

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.

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

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.

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.