TagDrop — Tag Dead Drop

TagDrop encodes self-contained digital content — HTML pages, images, audio clips, plain text — into one or more 2D barcodes (QR, Aztec, Data Matrix) for physical placement: on walls, along trails, inside objects. A finder scans the code(s) with the TagDrop Android app, or any browser using the tools below, to retrieve the content — no internet connection required once the codes are scanned.

Web Tools

Try the format right in your browser — no install required.

🧰 Generator

Create TagDrop QR codes from text, HTML, images, or audio — single files or full "paper" layouts. Supports key-code QR and passphrase encryption. Print-ready output.

📷 Reader

Scan TagDrop QR codes with your device camera, assemble multi-code payloads, browse paper directories, and follow tagdrop:// links between pages. Unlocks encrypted content via key-code or passphrase. Works fully offline after the first visit — handy on phones without a native TagDrop app, like iPhone.

🧪 Examples

A gallery of pre-generated sample codes: standalone payloads, multi-sector content, a paper set, a mini e-book of Markdown pages, a multi-location trail, and encrypted examples (key-code and passphrase).

📍 Community Drops Map

A live map of TagDrop codes placed in the wild by the community. Click a pin to see its location hint and status. Add your own drop by opening a pull request to docs/db/drops.json.

How it works

URI scheme: every code carries a tagdrop:<base41-cbor-sequence> URI — a CBOR sequence (version, type, payload map), Base41-encoded so it fits QR alphanumeric mode with minimal overhead. Content can optionally be DEFLATE-compressed, and IDs are content-addressed (SHA-256-based), so identical content always gets the same ID regardless of who created it.
Sectors carry a payload too big for one QR code: content splits into multiple self-describing sector codes that can be scattered across multiple physical locations and reassembled in any order, with an optional parity code that can recover a single missing sector.
Paper manifests describe a directory of files — each with its own short description — on one physical sheet, linked by ordinary relative links, tagdrop://@<root-hash>/<slug> (pinned to an exact paper), or tagdrop://<domain>/<slug> (a human-readable name), so a small static site survives being printed and scanned back in.
Trails, collections, and replies: link papers together with related hints, tag a loose set of stickers with a shared collection so they group into one card and map, or mark a code as a reply to another to thread a conversation across drops.
Encryption: content can be AES-256-GCM encrypted with a separate key-code QR, or locked behind a passphrase (PBKDF2-SHA256 — no second QR needed). Keys are retained so you only unlock once per device.
Forward-compatible: versioned, with unknown CBOR keys ignored, so the format can grow without breaking old readers.

Full details in the format specification (v1).

Android App

The TagDrop Android app scans codes with the camera, caches found content, and renders HTML/image/audio content offline — including navigation between pages of the same paper via tagdrop:// links. Encrypted content can be unlocked with a key-code QR or a passphrase; retained keys are managed in a dedicated Key Management screen.

Collections, History, and Map tabs let you revisit, locate, and manage everything you've found, with search and #hashtag filtering.
View as Rendered, Text, Hex, or CBOR — inspect any opened item's raw bytes alongside its normal rendering.
NFC tag read/write — write any TagDrop code to a blank or rewritable tag, then read it back with a tap instead of the camera.
Backup and restore all your scans, papers, and keys to a single file, on this device or another.
Replies thread a conversation across drops, even though each code stays independently scannable.

Build from source using DEVELOPING.md.

Related Projects

Communities and projects that share TagDrop's offline, public-space spirit.

Dead Drops

The original public USB dead-drop project by Aram Bartholl (2010) — USB drives embedded in walls for anonymous offline file sharing. TagDrop's direct inspiration.

#nfcdab

A DIY international digital art biennale using NFC tags, QR codes, and Wi-Fi to deliver art directly to smartphones in public spaces — no app or account required.

The world's largest geocaching community (since 2000) — hiding physical containers at GPS coordinates for others to find and log. TagDrop's geocaching inspiration: swap the logbook for a QR code.

OpenStreetMap

The free, community-built map of the world. TagDrop uses OSM for its map view.

Sneakerweb

A peer-to-peer web publishing protocol with no DNS, registrars, or hosts — sites are traded as .snk files over physical storage media ("sneakernet") and merged with the Willow protocol. Shares TagDrop's physical-media-as-network spirit, at the scale of a whole synced, mergeable website rather than a single sealed drop.