markitdown-web

MarkItDown Web — convert documents to Markdown entirely in your browser, with no server. A weekly GitHub Actions workflow builds the microsoft/markitdown Python package to WebAssembly (via Pyodide) and publishes it as an offline-capable PWA to GitHub Pages.

Live site: https://sloth-os.github.io/markitdown/

What it does

• Converts PDF, DOCX, PPTX, XLSX, XLS, HTML, CSV, JSON, EPUB, IPYNB, ZIP, Outlook MSG, RSS and plain text to Markdown — the same output as the markitdown CLI, because it is markitdown running under Pyodide.
• Works offline. The service worker precaches the entire engine (~54 MB: Pyodide + wheels + onnxruntime-web + the magika model). After the first load the app runs with the network fully disconnected.
• PWA File Handling. The manifest registers the app as an OS handler for document types, so you can "Open with → MarkItDown Web" from the file manager (Chrome/Edge on desktop, "Open in app" on Android) and the file arrives through the File Handling API (launchQueue).
• Files never leave the device — conversion happens 100 % client-side.
• "keep data URIs" toggle. By default markitdown truncates embedded images to keep the markdown readable — DOCX/EPUB/HTML show a truncated placeholder (data:image/png;base64… → data:image/png;base64...), while PPTX substitutes the image's filename (![image.png](Picture2.jpg)). Enable the toggle in the result view to retain the raw base64 image data for all formats, matching the CLI's --keep-data-uris. Applies to DOCX/EPUB/HTML (markdownify) and PPTX (direct emission), and re-converts the file you're viewing when flipped. The choice is remembered per browser.
• Updated weekly from upstream microsoft/markitdown@main, so new converters and fixes roll out automatically.

Supported inputs

Anything markitdown supports that can run in the browser sandbox: .pdf .docx .pptx .xlsx .xls .html .htm .csv .tsv .json .xml .md .txt .log .ipynb .epub .zip .msg .rss .atom and more. Audio transcription, image captioning (both need external services) and exiftool metadata are out of scope for the offline build.

How it works

┌─────────────────────────── browser ────────────────────────────┐
│                                                                │
│  JS side (app.js / magika.js)        Python side (Pyodide)     │
│  ───────────────────────────         ────────────────────      │
│  file → magika feature extract ┌──▶ api.py                    │
│       → ONNX inference         │    (onnxruntime stubbed out)  │
│       (onnxruntime-web) ────────┘ markitdown.convert_stream │
│  prediction {mime, ext, label} ▲                         │
│  ────────────────────────────────────┘                         │
│                                                                │
│  service worker precaches the whole engine → offline mode      │
└────────────────────────────────────────────────────────────────┘

• Pyodide 0.29.5 (Python 3.13) provides the interpreter plus wasm builds of numpy, pandas, lxml, Pillow, cryptography, requests, …
• Pure-python wheels (markitdown, python-pptx, mammoth, openpyxl, pdfminer.six, pdfplumber, markdownify, magika, …) are vendored into site/wheels/ and installed at runtime with micropip from the virtual filesystem — no PyPI access needed at runtime.
• magika (markitdown's content sniffer) needs onnxruntime, which has no Pyodide build. The browser build instead runs the same ONNX model with onnxruntime-web in JS, replicating magika's feature extraction (beg/end byte windows) and its high-confidence threshold logic. The prediction is handed to Python as a stream_info guess — outputs match the native magika (verified by the test suite against magika on CPython). Inside Pyodide, onnxruntime is a stub module so import markitdown succeeds.

Repo layout

Path	What
src/index.html, src/styles.css	App shell (drop zone, queue, result view)
src/js/app.js	Engine boot, queue, drag&drop/paste, launchQueue file handling
src/js/magika.js	magika re-implementation on onnxruntime-web
src/js/ort-setup.js	Loads onnxruntime-web, configures single-thread wasm
src/js/sw-template.js	Service worker template (precache manifest injected at build)
src/python/api.py	Pyodide-side glue: onnxruntime stub, magika stub, convert()
src/manifest.webmanifest	PWA manifest incl. file_handlers
scripts/build-site.sh	Assembles site/ from all the pieces above
.github/workflows/deploy-pages.yml	Weekly build + test + Pages deploy
tests/e2e-test.mjs	Playwright end-to-end suite (boot, conversions vs Python reference, keep-data-URIs toggle, offline, manifest, JS-magika vs native-magika agreement)
tests/race-probe.mjs	Playwright race probe for the keep-data-URIs reconvert path: deterministic mid-conversion toggle flips (stalled arrayBuffer + timed flips), view-yank, duplicate-conversion, clear-queue stale-index, error-pane and boot-retry scenarios (S1–S7)
tests/fixtures/, tests/reference-*.json	Test documents + outputs produced by native markitdown (reference-keep-data-uris.json holds the --keep-data-uris outputs)

Building locally

# assumes a markitdown checkout at ~/software/markitdown
bash scripts/build-site.sh [path/to/markitdown]

# serve + test
python3 -m http.server 8977 --directory site &
cd tests && TEST_BASE_URL=http://localhost:8977/ node e2e-test.mjs

The deploy workflow runs the same script against a fresh checkout of microsoft/markitdown@main every Monday 03:00 UTC, then publishes only if the end-to-end tests pass.

PWA notes

• Offline: the first load installs the service worker, which precaches all 50+ assets. Subsequent loads work with navigator.onLine === false (this is asserted by the e2e suite).
• File Handling: file_handlers in the manifest + a launchQueue consumer in app.js. Install the PWA (install button in the URL bar / "Install app" menu), and the OS will offer MarkItDown Web when opening documents. Files can also arrive by drag & drop, file picker, or paste.
• Weekly builds rotate the service-worker cache atomically (build-id-stamped cache name), so engine updates land on the second visit.

License

MIT, matching upstream markitdown. This repository is a build/packaging project and is not affiliated with Microsoft.