Tessera
A letter, waiting for its day.
Tessera is a tool and an open format for writing letters meant to be opened years or decades from now — to a child at eighteen, to yourself at sixty, to a stranger in 2126. You write in a plain-paper room that never leaves your device, then seal the letter into a folder of files and a matching print kit. Sealing generates a hospitality token, cut in two: one half stays with you, the other travels with the letter, so that decades later the matching halves confirm it's real.
Nothing about Tessera depends on a company staying in business. The format is public domain — one letter, one folder of plain text files, readable with nothing but patience. The tool is a static page with no build step and no dependencies, easy to fork or mirror. No accounts, no cloud storage of your letters, no delivery service promising to email your future self.
It's still being built in the open, one version at a time. What's live now — writing, sealing, the token, the print kit, the local registry, and a first set of open-when letters for the nights that need them most — is v0.1. Receiving and verifying a letter, reminders without a server, and optional passphrase privacy are next; occasions, a bound-booklet export, and eventually a shared commons follow after that. The repo is public the whole way through.
A quiet, distraction-free composer that runs entirely on your device — no account, no server. Drafts autosave to localStorage and the page works offline via a service worker.
One action produces two things: a folder of plain files (the letter, a machine-readable manifest, a self-describing README, checksums, the token art) and a print kit typeset for paper — cover sheet, opener instructions, token sheet included.
Named for the tessera hospitalis, the token ancient hosts broke in two so descendants — strangers to each other — could reunite the halves and be recognised. Every sealed letter generates one: a deterministic two-half SVG, one half kept, one half travels with the letter.
A calibration corpus of prompts for the letters that matter most: written for a specific bad night rather than a date — open when you're sad, when you doubt yourself, when it's 3 a.m. and you can't sleep.
A local, on-device ledger of every letter sealed, with a printable register page. No account, no cloud, nothing that outlives the machine unless you print it.
The print kit contains everything a letter needs; the digital folder is convenience. Tessera is honest that no cryptography can stop someone opening an envelope early — custody and care do that, the way they always have.
The spec is CC0 — public domain, forever. One letter is one folder of plain text, legible in 2126 without any particular software. The tool itself is a static page under MIT: no build step, no npm install, forkable to a USB stick.