Dewey

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Inspiration

Everyone has a Downloads folder like mine. Mine is buried under too many PDFs of courses, scanned documents, tickets and bills.

In Morocco it is worse than usual. Bills, bank statements and leases arrive in French, Arabic and English, often mixed inside one page, as scans and WhatsApp forwards named WhatsApp Doc 2023-10-22 at 07.05.19.pdf. Every file manager searches names and nothing files it for you.

I wanted the folder to sort itself, without any of it leaving my phone.

What it does

Free, with no ads and no account. A real document scanner with edge detection, perspective correction and OCR, plus fourteen PDF tools: merge, split, extract, rotate, reorder and delete pages, sign, compress, add or remove a password, watermark, page numbers, and PDF to and from images. The page tools open a document as thumbnails you drag, so you never type a page number.

Librarian, the paid tier:

• Sort. Point Dewey at a folder and tap once. It reads every PDF, works out what each one is, creates folders and files them. Anything it is not sure about goes to a review queue instead of being guessed at, and the whole sort can be undone.
• Ask. "When is my Lydec bill due and how much is it?" The answer comes out of the documents themselves, with the files it used shown beside it.
• Bills and notes. Detected bills with vendor, amount and due date, grouped by what is due first, plus notes of your own. Both have home screen widgets.

How we built it

• Kotlin, Jetpack Compose, Room, WorkManager. Sorting four hundred files is a WorkManager job, not a screen's, so closing the app does not cancel it.
• On-device embeddings. multilingual-e5-small through ONNX Runtime, with a Kotlin SentencePiece tokenizer checked token for token against HuggingFace on French, Arabic, mixed script and malformed input.
• Sorting is a nearest neighbour lookup, not a cloud call. A category is another point in the same embedding space as the documents, so filing a whole folder sends nothing anywhere.
• Storage Access Framework, not MANAGE_EXTERNAL_STORAGE. You grant one folder and Dewey gets that folder, nothing else.
• Gemini through Firebase AI Logic composes answers from retrieved passages only, so no API key lives in the source.
• RevenueCat for the entire purchase path.

How we used RevenueCat

Librarian is a single entitlement, dewey_app_pro, sold as monthly and annual packages on the current offering.

• Purchases.configure at app start, with the signed in user's id as appUserID, so a returning subscriber is never briefly anonymous.
• UpdatedCustomerInfoListener plus an initial awaitCustomerInfo, so every screen reacts the moment the entitlement changes.
• A custom paywall driven entirely by the offering. Prices, the per month price, the "Save 44%" badge computed from the two real products, and trial wording all come from awaitOfferings. Nothing is hardcoded.
• awaitPurchase on the main thread, and awaitRestore, which only reports success when the entitlement actually came back.
• An optional account. Firebase email sign in calls awaitLogIn(uid), so a purchase follows the person to a new phone; signing out calls awaitLogOut.
• RevenueCat's Customer Center for restores, cancellations and plan changes inside the app, plus the managementURL link.
• The paywall appears where the value is: on the locked Documents, Notes and assistant screens, which show what they would do before asking for anything.

It runs on RevenueCat's Test Store deliberately. This entry is judged on a repo and a video, so a separate demo build type carries the test key and the release variant carries no purchase key at all.

Challenges we ran into

• Arabic that looks right but reads wrong. Text extraction loses content at direction boundaries. Every generated test document is round tripped and gated at 92% token recall, so a corrupted document cannot quietly skew the evaluation.
• A tokenizer that is subtly wrong never crashes. It just produces slightly worse vectors forever, which is why it is tested against the reference implementation rather than eyeballed.
• Confident misfiles cost more than review. The sort threshold sits high on purpose. A looser one pulled an English transcript into "Papers", so it was dropped.
• Android refuses to grant the Download root through SAF since Android 11. We kept SAF anyway and documented the trade rather than asking for the whole disk.
• PDFBox's importPage already appends the page. Wrapping it in addPage put every page in twice. Found on a real device, fixed, and pinned by tests that read the output PDFs back.

Accomplishments that we're proud of

• On a live run in the demo, 100 unnamed documents became 11 folders in one tap: 98 filed, 2 held for review rather than guessed at.
• Sorting makes zero network calls.
• 81% recall@1 and 95% recall@3 for search across three languages.
• Over 760 unit tests, including PDFBox round trips on real documents.
• The free half is a complete app on its own: a scanner and fourteen PDF tools, no ads, no account.

What we learned

The honest place for a paywall is the part that costs something to build and saves someone an afternoon. The scanner and the PDF tools are a complete free app. What Librarian sells is the reading.

What's next for Dewey

App Check on the Firebase config, a Play Store listing with real products on the same RevenueCat offering, and learning categories from the folders people already keep. That last one is already measured: a folder of your own documents describes them about three times more sharply than any description we wrote.

Built With

• android
• datastore
• firebase
• firebase-ai-logic
• firebase-auth
• gemini
• jetpack-compose
• jetpack-glance
• kotlin
• kotlin-coroutines
• material-design
• ml-kit
• onnx
• onnx-runtime
• pdfbox
• python
• revenuecat
• room
• sentencepiece
• storage-access-framework
• workmanager